UP TGT Biology 2021 Official Paper (Previous Year Paper)

The correct answer is Centriole.

Explanation :

• Centrioles are present in animal cells and absent in plant cells.
• They are the microtubules organizing regions which organize the position of mitotic spindles during cell division.
• Plants have a rigid cell wall that can itself organize the spindle forming microtubules during cell division.

Key Points

• Structure of Centriole :
• A centriole is a barrel-shaped structure located in the cytoplasm of animal cells.
• A pair of centrioles make the organelle centrosome.
• The centrioles appear as 2 cylinders at right angles to each other.
• The wall of the centriole is made of 9 triplets fibres arranged around a central axis.
• Each fibre consists of 3 sub-fibres or sub-tubules lying parallel to each other.
• It looks like a cart-wheel structure with a central rod or hub radiating 9 spokes, each of which is connected to a fibre.
• ​Functions of Centriole : 
• They are involved in mitosis for formation of spindle fibers.
• Spindle fibres attach to the kinetochore discs present at the centromere and help in the movement of chromatids during chromatid separation.
• They also form the mitotic apparatus during mitosis or meiosis.
• In primitive flagellates, they function as basal bodies for the flagella.

Additional Information

• ​A large central vacuole :
• ​The vacuole is the membrane-bound space found in the cytoplasm of plant cell.
• The membrane of the vacuole is known as tonoplast.
• It contains water, sap, excretory product and other materials not useful for the cell.
• 70 S Ribosome :
• Ribosomes are very important cellular component that are used for synthesis of proteins from RNA.
• The 70S ribosome consists of 2 subunits - 50S and 30S, which take part in the translation process.
• 70S ribosomes are mostly found in prokaryotic cells, but are also present in the chloroplast in plant cell.
• This is supported by the 'Endosymbiotic Theory' that proposes that chloroplasts and mitochondria are remnants of primitive prokaryotic cells that became a part of plant cell to perform specific functions.
• These cells have later evolved as the cell organelles to perform photosynthesis and respiration.
• 80 S Ribosome :
• ​Plant cells have three distinct ribosome species; 80 S ribosomes in their cytosol, 70 S-like ribosomes in their chloroplasts and mitochondria.
• Eukaryotic ribosomes are 80S ribosomes that consists of 2 subunits- 60S and 40S.

The correct answer is Hardened resinous secretion.

Explanation:

• 'Amber' is a fossilized form of hardened resinous secretion.
• Resin is a sticky, viscous substance secreted by plants to protect them from predators and pests.
• Amber is made from resin exuded from tree bark, but it can also be found in the heartwood.
• Resin protects trees by filling gaps in the tree bark.
• When resin covers a break that is caused by a chewing insect, it hardens and forms a seal.
• Thus amber often contains insects preserved in it as they might have got stuck in the sticky resin years ago.

Important Points

• Colour - All shades of yellow.
• Shape - Irregular nodules, rods or drop-like shapes.
• Occurences - Largest deposits are found along the shores of Baltic Sea.
• Some other properties:
• It may contain microscopic air bubbles.
• Baltic amber often contain minute hair-like inclusions, apart from insects.
• The surface changes its colour and opacity on exposure to oxygen in air - it becomes darker and opaque.
• When kept in oxygen-free environment, they retain their original colour and appearance.
• Uses -
• Deeply coloured translucent or transparent forms are valued as gems.
• Used for making decorative items and jewelry.
• Healing agent in folk medicine.
• Study of fossils that are preserved inside the hardened resin.
• It is also used for aesthetic purposes.
• In ancient times, it was used as a natural magnifier.
• Transparent amber with a convex surface was used as burning lenses for concentrating sun's rays.

A dwarf shoot with two needles is found in Pinus Sylvestris.

Key Points

• Pinus is a ''Coniferous gymnosperm''.
• These are large trees having pyramidal or ''excurrent shape'' like a ''Christmas tree''.
• Pinus has both male and female cones present on the same tree.
• Male cone occurs in a cluster, subterminally on lower long braches.
• The female cones develop in a group of 2-6 on the upper long branches of the tree.
• It has a sporophytic plant body that is differentiated into root, stem and needle-like leaves.
• There are 2 types of branches - long shoot and dwarf shoot.

Important Points

• The leaves of Pinus are of 2 types:
• Foliage - are large, needle-like and present at the apex of dwarf shoots only.
• Scaly - are thin, brown, scale-like and is present on both long and dwarf shoots.
• Foliage leaves vary in number from 1-5 in different species.
• The dwarf shoot with needles is called a spur.
• Depending on the number of needles, spurs can be of the following types:
• Unifoliar - Only 1 leaf or needle present at the apex of dwarf shoot. E.g. - Pinus monophylla.
• Bifoliar - with 2 needles. E.g. - Pinus sylvestris.
• Trifoliar - with 3 needles. E.g. - Pinus gerardiana.
• Quadrifoliar - with 4 needles. E.g. - Pinus quadrifolia.
• Pentafoliar - with 5 needles. E.g. - Pinus wallichiana.

The correct answer is Perianth.

Explanation:

• Now the Gramineae family is known as Poaceae family.
• Graminae is a grass family of monocotyledonous flowering plants.
• The Poaceae are the world's most important food source.
• Grass, wheat, rye, and other cereal grains are primary members of the Gramineae family.

Important Points

• The inflorescence present in Graminae is called spikelet.
• Each spikelet consists of a short axis called rachilla, which bears a number of bracts, bracteoles and flower.
• The 2 lowermost bracts are sterile and termed as empty glumes.
• The third bract is flowering and called as lemma.
• There is a bracteole called palea placed opposite the lemma.
• Each spikelet may contain one or more flowers, where the lemma bears the flower in its axil.
• The perianth is the outer part of a flower that includes the calyx (sepals) and corolla (petals).
• In Graminae, the perianth is represented by lodicules.
• Lodicule - is a structure that consists of one to three small scales at the base of the ovary.
• In the Graminae family, two or three lodicules (minute scales) represent the perianth.
• The lodicules are present between the lemma and ovary base.
• Their main function is to swell rapidly at maturity to force apart the lemma and palea.
• Thus they help in assisting anthesis, allowing the anthers and stigma to emerge for pollination.

The correct answer is Head.

Explanation: 

Tentorium - It is formed by ingrowths of the exoskeleton (made of chitin), which fuse in various ways to provide rigid support for the muscles of the head.

Key Points

• The common cockroach is scientifically known by the name Periplaneta americana.
• General Characteristics of Cockroach :
• They are brown or black-bodied & a dioecious animal, with separate male and female sexes.
• They are included in class Insecta of Phylum Arthropoda.
• They are nocturnal omnivores that live in damp places throughout the world.
• The entire body is covered by a hard chitinous exoskeleton.
• The body of the cockroach is segmented and divisible into three distinct regions – head, thorax, and abdomen.

1. Head -

• Head is triangular in shape, head capsule bears a pair of compound eyes.
• In front of the eyes, membranous sockets are present, out of which two antennae protrude out.
• The head also has appendages that bear similarity to the mouthparts, such as the labrum, a pair of mandibles, a pair of maxillae and a labium.
• There is also a flexible lobe called the hypopharynx that acts as a tongue.

2. Thorax -

• The thorax is further divided into - prothorax, mesothorax, and metathorax.

3. Abdomen -

• The abdomen is made up of 10 segments.
• The 7th, 8th, and 9th sterna form a genital pouch in females.
• The male cockroach has thread-like anal styles, which are missing in the female cockroach.​​

Important Points

• The endoskeleton is formed by the internal extensions of the exoskeleton.
• Such endoskeletal elements are known as apodemes, which help in attachment of muscles.
• The apodemes of the head form a characteristic structure called tentorium.
• The tentorium is present below the occipital foramen in the head.
• It has a central space for the passage of nerves and 3 pairs of arms - anterior, posterior and dorsal.
• The apodemes of the thoracic region is meant for attachment of leg muscles.
• Endoskeleton is absent in the abdomen.

Concept-

• Cycas are seed-producing plants that belong to the Gymnosperms.
• Cycas have a dominant diploid sporophyte phase in their life cycle.
• It is strictly dioecious, i.e., male and female organs are borne on separate plants.
• The microspores develop in the microsporangia after meiosis.
• The male gametophyte development takes place in 2 phases, pre- and post-pollination.

Important Points

• The male gametes (spermatozoids) of Cycas are the largest in the plant kingdom.
• Their size varies from 180-210µm and are visible to the naked eye.
• The spermatozoids of Cycas are top-shaped, motile, and multiciliate.
• They have 5-6 spiral bands of thousands of cilia, which help them move in the pollen tube.

Additional InformationMale Gametophyte Development -

1. First Stage of development -

• The development of male gametophyte takes place in the sporangium.
• The nucleus divides into two and one moves to the lower side and is separated from the other by a crescent-shaped wall.
• This results in two unequal cells - lower smaller prothallial cell, upper larger antheridial cell.
• The antheridial cell divides to form a generative cell and a distal tube cell.
• This is the 3-celled stage at which the pollen grains are shed as the microsporangia dehisce.

2. Second Stage of development -

• Pollen grains get stuck to the pollination drop on the ovule.
• The pollination drop is a viscous fluid that collects at the micropyle end and gradually dries up.
• As a result the pollen grains are sucked into pollen chamber and the micropyle is sealed.
• After a period of rest of up to 4 months, the exine breaks and pollen tube comes out.
• Pollen tube enters the archegonial chamber through the nucellar tissue.
• The generative cell divides to form a stalk cell and a body cell.
• Two blepharoplasts appear at 2 poles of body cell nucleus.
• The body cell divides longitudinally to form 2 sperm cells.
• Each sperm cell develops into a spermatozoid (sperm) and blepharoplast into cilia.
• The sperm mother cell ruptures to release the sperms into the pollen tube.

Concept -

• Kingdom Animalia is divided into sub-groups which is known as Phylum.
• There are 11 phyla in the kingdom Animalia.
• Porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata, Chordata.
• Pila is the example of the kingdom Mollusca.
• Mollusca is the second largest phylum that includes "soft bodied and shelled" animals.

Explanation-

• Pila is herbivorous, feeding on algae and plants.
• The mouth leads into a cuticle-lined buccal cavity.
• On the floor of the buccal cavity, there is a structure called odontophore.
• Odontophore is an elongated, muscular, and cartilaginous structure that bears a membranous belt called a radula.
• The radula which lies in a radular sac has transverse rows of teeth.
• Each row has seven teeth: 2 marginal and 1 lateral tooth on each side and 1 central tooth in the middle.
• Thus, giving a formula 2, 1, 1, 1, 2.
• These help to cut the food into bits.

Therefore, in Pila 21112 teeth are present in each row of radula.

Additional Information

• Pila is also called an Apple snail.
• Pila respire by gills in water or by pulmonary sac on land.
• The larva of pila is veliger.

The correct answer is a - 3, b - 2, c - 4, d - 1.

Explanation:

Epistatic gene-

• An epistatic gene is one that masks or hides the phenotypic effect of another gene.
• Thus, Epistatic gene masking the action.

Translocation-

• Chromosome translocation is a genetic condition that results in the Interchromosomal rearrangement.
• Thus, translocation causes interchromosomal rearrangement.

Neomorph-

• A neomorphic mutation results in a dominant gain of gene function that is not the normal function.
• Changing the dose of a wildtype gene has no influence on the phenotypic of a neomorph.
• Hence, neomorph produce a phenotype different from the wild gene.

Co-dominance-

• When the F₁ generation resembles both the parents, and both the parental characters are expressed simultaneously, then the phenomenon is called Co-dominance.
• For example, 'AB' type blood group is possible when allele 'A' and 'B' come together and since both the allels are expressing their effects in F₁ generation, they are co-dominants.
• Hence, Co-dominance character is controlled by two genes.

The correct answer is more than 1.

Hint

Respiratory substrate & Respiratory Quotient (RQ) 

• The respiratory substrate is broken down to release energy in the process of respiration. Aerobic and anaerobic respiration are the main two types of respiration that occur in the presence or absence of molecular oxygen. Glucose is the most common respiratory substrate present in plants.
• During aerobic respiration, O₂ is consumed and CO₂ is released.
• "The ratio of the volume of CO₂ evolved to the volume of O₂ consumed in respiration is called the Respiratory Quotient (RQ) or Respiratory Ratio."
• Respirometer is an instrument used for measuring the rate of respiration as well as R.Q.

RQ Value is calculated using the given formula : 

$RQ = \frac{Volume\ of \ CO_2 \ evolved }{Volume\ of \ O_2 \ consumed}$

The respiratory quotient depends upon the type of respiratory substrate used during respiration.

Explanation:

RQ of Organic acids (More than 1)

• Organic acids like - Malic acid (Refer below reaction), Tartaric acid, Oxalic acid are rich in O₂ and require less O₂  for their oxidation, so when the organic acids are oxidized in respiration, the value of R.Q. is greater than one. The reaction & RQ is given below :

​C₄H₆O₅ (Malic acid) + 3O₂  → 4CO₂ + 3H₂O + Energy

$RQ = \frac{Volume\ of \ CO_2 \ evolved }{Volume\ of \ O_2 \ consumed} = \frac{4}{3} = 1.33$

Important Points

Significance of RQ:

• Helps in determining the type of respiration being performed.
• Determine the nature of the respiratory substrate that oxidized the transformation of the substrate and the biochemical mechanism of respiration.
• Knowing the metabolic rate.
• Determination of various pathological conditions like acidosis, alkalosis, etc.

Additional Information

1. RQ of Succulent plants  [Zero]

• In succulent plants like - Bryophyllum, Opuntia, etc., stomata remain open during the nighttime. So, at night when oxygen is absorbed, the carbohydrates are partially oxidized to organic acids without the formation of CO₂. So, the value of R.Q. remains zero.
• During the day, the value of RQ remains zero because the CO₂ released during respiration is used up as a substrate for photosynthesis

​2C6H12O6 (Glucose) + 3O2  → 3C₄H₆O₅ (Malic acid) + 3H2O + Energy

$RQ = \frac{Volume\ of \ CO_2 \ evolved }{Volume\ of \ O_2 \ consumed} = \frac{0}{3} = 0$

      2. RQ of Carbohydrates [1]

• When carbohydrates are used as substrate and are completely oxidized, the RQ will be 1, because equal amounts of CO₂ and O₂ are evolved and consumed, respectively.

​ C₆H₁₂O₆ + 6O2  (Glucose) → 6CO₂ + 6H2O + Energy

$RQ = \frac{Volume\ of \ CO_2 \ evolved }{Volume\ of \ O_2 \ consumed} = \frac{6}{6} = 1$

     3. RQ of Fats [Less than 1]

• Fats need more amount of O₂ for their oxidation as compared to other substrates. Fats are usually present in seeds as storage food in plants.
• Fats need more amount of O₂ for their oxidation as compared to other substrates.
• R.Q. value is less than one or unity in the aerobic respiration of fats**.**

​2C5 H98O6 (Tripalmitin)+ 145O2  → 102CO2 + 98H2O + Energy

$RQ = \frac{Volume\ of \ CO_2 \ evolved }{Volume\ of \ O_2 \ consumed} = \frac{102}{145} = 0.7$ (Less than 1)

     4. RQ of Proteins & their derivatives [Less than 1]

• Proteins are building blocks of the living body and are made up of amino acids.
• When the cells are going to starvation, then proteins act as a respiratory substrate.
• When proteins are respiratory substrates the ratio would be about 0.9.
• Protein structures vary with changes in amino acid sequence.
• So, the value of R.Q. also varies from 0.8 - 0.9 depending upon the structure of different amino acids.

​2C3H₇O₂ N(Alanine)+ 6O2  → CO(NH₂)₂  (Urea) + 5CO2 + 5H2O + Energy

     5. RQ of Aerobic respiration [More than 1]

• In aerobic respiration, when respiratory substrate is fat or protein, R.Q is less than 1.
• When carbohydrate is the substrate, R.Q is 1.

The correct answer is Mutation theory.

Key Points

• Charles Darwin : British naturalist and evolutionary biologist Charles Darwin is known as the "Father of Evolution", credited for the theory of natural selection.
• Pangenesis theory (1868):
• It was given by Charles Darwin.
• It states that every part of the body emits tiny particles called gemmules which migrate to the gonads and are transferred to offspring.
• These particles are then transmitted to the next generation and are responsible for the transmission of characteristics from parent to offspring.
• Mutation theory (1901) :
• Dutch botanist and geneticist Hugo de Vries gave rise to the Mutation theory.
• According to his theory, mutation causes evolution by formation of new species or speciation.
• Mutations refer to the changes in the genes of organisms that greatly altered the organism.
• These changes are passed down to the next generation and lead to the development of new species.

Additional Information

Darwin gave rise to two theories 

1. Theory of Natural Selection (1859) : The slightest difference in traits like color or design can help or proves useful for animal or plant live, survive and reproduce better in the wild, that will retain naturally and get transferred to next generations. Various species originated from a single species as a result of adaptation to the changing environment, as per natural selection.
2. Theory of survival of fittest (1869) : This means that individuals in a population, or community, are more likely to survive if they are fit and the rest will die.

Concept-

• In angiosperm flower, the male and female reproductive structures, the androecium and the gynoecium differentiate and develop.
• The gynoecium represents the female reproductive part of the flower.
• The gynoecium may consist of a single pistil or may have more than one pistil.
• Each pistil has three parts: the stigma, style, and ovary.

Explanation-

• The ovule is also known as integumented megasporangium.
• The megasporangium is a small structure attached to the placenta by means of a stalk called funicle.
• Each ovule has one or two protective envelopes called integuments.
• Enclosed within the integuments is a mass of cells called the nucellus.
• Cells of the nucellus have abundant reserve food materials.
• Located in the nucellus is the embryo sac or female gametophyte.
• The embryo sac develops from a single megaspore formed from the megaspore mother cell inside the megasporangium.

Therefore, the embryo sac is bounded by the wall of megasporangium.

Additional InformationEndosperm

• It is the nutritive tissue for the developing zygote.
• It may or may not be present in the mature seed.

Megaspore

• In a majority of flowering plants, one of the megaspores is functional while the other three degenerate.
• Only the functional megaspore develops into the female gametophyte (embryo sac).

Litmus is obtained from lichen.

Key Points

• Litmus is a mixture that is made from different dyes which can be taken from lichens.
• Lichens are symbiotic associations i.e., mutually beneficial associations between algae and fungi.
• Algae prepare food for fungi and fungi provide shelter and absorb mineral nutrients and water for their partner.
• The algal component is known as photobiont and fungal component is known as mycobiont.
• So close is their association that if one saw a lichen in nature one would never imagine that they had two different organisms within them.
• Litmus paper is used to test whether a solution is an acid or an alkali.
• The paper can then be used to give a rough indication of the pH value of a solution.
• Blue litmus paper will turn red when acid is present.
• Red litmus paper will turn blue when alkaline solutions are present.

Important Points

• A mixture of certain coloured organic compounds forms litmus.
• These compounds are obtained from lichens like Roccella tinctorum and Lecanora tartarea.
• The compounds are extracted by treating the lichens with ammonia, potash and lime in the presence of air.
• Litmus has been partially separated into different compounds like erythrolitmin, erythrolein, azolitmin, etc.
• These compounds have been identified as derivatives of the heterocyclic compound phenoxazine.

Additional Information

Red algae

• The members of Rhodophyceae are commonly called red algae because of the predominance of the red pigment, r-phycoerythrin in their body.
• The majority of the red algae are marine with greater concentrations found in the warmer areas.
• They occur in both well-lighted regions close to the surface of the water and also at great depths in oceans where relatively little light penetrates.
• Agar is obtained from red algae, to be used as a gelling substance.

Bryophyta

• Bryophytes include the various mosses and liverworts that are found commonly growing in moist shaded areas in the hills.
• Bryophytes are also called amphibians of the plant kingdom because these plants can live in soil but are dependent on water for sexual reproduction.
• They usually occur in damp, humid, and shaded localities.
• They play an important ecological role as they help in initiating soil formation on barren rocks, nutrient cycling, and maintaining soil moisture.

The correct answer is G U G.

Concept:

• Central dogma of molecular biology states that flow of genetic information takes place from DNA to RNA to proteins.
• Transcription of DNA to RNA is based on the complementarity of their strands.
• However, no such complementarity exists between the RNA and the proteins for translation to take place.
• Evidences show that changes in nucleic acids also caused changes in the amino acids of the proteins.
• This suggested the existence of a Genetic Code that directs the synthesis of amino acids that form the proteins.
• The relationship between the sequence of nucleotides on mRNA and sequence of amino acids in the polypeptide is called genetic code.
• It was George Gamow who suggested that if the 4 nitrogen bases of nucleic acids have to code for the 20 non-essential amino acids produced in the body, the code should constitute a combination of bases.
• The nitrogen bases include Adenine (A), Guanine (G), Cytosine (C) and Uracil (U) for an RNA.
• A permutation combination of 2 bases would give: 4² = 16 amino acids only. Thus, it has to be a combination of 3 bases giving: 4³ = 64 codons.
• Thus it was concluded that 64 codons would code for the 20 amino acids with some codons being signal codons too.

Explanation:

• From the above table we can see that GUG is a codon that codes for valine (amino acid).
• Formylated-methionine is encoded by the codon AUG, which is also known as the start codon.
• As a result, during protein synthesis within the ribosome, formylated-methionine is known to be the first amino acid to dock.
• AUG is a dual function codon: it codes for methionine and it also acts as a initiator codon.
• Usually the codons are non-ambiguous, meaning they code for only one specific amino acid in all organisms.
• GUG is an exception to this rule.
• When AUG codon is absent, GUG operates as a start codon and codes for formylated-methionine as initiator codon for protein synthesis.
• For example, the lacI region of E. coli lac operon has GUG as initiator codon.

Thus, G U G codon usually codes for valine but can also code for formylated-methionine as initiator codon.

Additional Information

• The salient features of the genetic code are:
• Triplet codon - Each codon is a triplet of any 3 bases. 61 of the codons code for amino acids and 3 codons act as STOP codons.
• Start codon - The codon AUG acts as a START codon or initiator codon as well as codes for Methionine(Met).
• Unambiguous & Specific - One codon codes for only one amino acid.
• Degenerate - Some amino acids are coded by more than one codon.
• Contiguous - The codon in mRNA is read in a continuous manner without any punctuation.
• Universal - A codon codes for a specific amino acid for all organisms. Exception - Some mitochondrial codons and some protozoans.

Concept-

• Gene is the basic unit of inheritance.
• Genes are hereditary markers from which control various characteristics like skin colour, height, etc.
• Gene which controls more than one character is called a pleiotropic gene.
• This gene shows multiple phenotypic effects.

Explanation-

• Phenylketonuria (PKU) is one such disorder that is caused due to a single gene mutation.
• The mutation is caused in the gene encoding phenylalanine hydroxylase enzyme.
• Affected people lack this enzyme, which can convert phenylalanine to tyrosine.
• Lack of the enzyme results in accumulation of phenylalanine, which gets converted to phenylpyruvic acid.
• Phenylpyruvic acid has adverse effects on the body:
• Mental retardation
• Reduction of hair
• Skin pigmentation
• Thus, we can see that a single gene mutation is causing multiple phenotypic expressions.

Additional InformationPolygenic Inheritance -

• Polygenic inheritance was first described by Nilsson Ehle.
• It is the inheritance of characters in which one character is controlled by many genes.
• Here, the intensity of character depends upon the number of the dominant alleles.
• For example, human skin colour which is spread across a gradient and not distinct.
• It is the result of the additive effect of each allele.

Concept -

• The study of birds is called ornithology.
• Columba is a bird that is included in the class Aves of phylum Chordata.
• Birds are warm-blooded or Homeothermic i.e., body temperature remains almost constant.

Explanation-

• Birds have very sharp vision, that enables them to see better during flight.
• Pigeons have side-facing eyes, which decreases their binocular vision but increases the monocular vision.
• Pecten is a unique comb-like structure inside the vitreous humor of eyes.
• It is of pleated-type in pigeon that protrudes from the retina into the vitreous chamber of eye.
• It contains blood supply that is thought to provide oxygen and nutrients to the avascular retina.
• The pecten is derived from the choroid in the eye of a bird.
• It also regulates the pressure of liquid present in the eye.
• Due to pecten birds have acute vision and telescopic vision.

Therefore the pecten of Columba (Pigeon) is derived from the choroid.

Additional InformationRetina

• It is a transparent layer forming the inner coat of the eye, it supports the choroid layer.
• The rays of light, on entering the eyeball, converge and form an image on the fovea—the posterior part of the eye on the retina.

Lens

• It is a transparent, biconvex structure situated between the iris and vitreous humor.
• Its function is to focus the luminous rays; these rays form a perfect image on the retina.
• With age, the central portion of the lens compresses by the surrounding fibres and results in opacity, which is called a cataract.

Sclera

• It is the outermost coat of the eyeball. It maintains the strength and structure of the eyeball.
• It is also known as the white of the eye.

The correct answer is  Commensalism.

Key Points

Species interaction or population interaction

• In an ecosystem living organism continuously interact and influence the other organism and with their environment directly or indirectly, in order to carry out their vital processes.
• This is called species interaction or population interaction.
• Sometimes interaction between species or population can be - useful, harmful or neutral to one of the species or both.
• Types of interaction between organisms can be broadly classified as follows :

1. Positive interaction: In this type, interacting organisms or populations benefit one another. The benefit may be in respect of - food, shelter, substratum, or transportation.
2. Negative interaction: In this type, one of the interacting organisms is benefited and another is affected (harmed). One organism or population may eat other organisms, compete for food or excrete harmful waste.

Explanation:

Commensalism (Neutral type of interaction)

• In this type, one organism is benefited while the other organism is neither benefited nor harmed.
• Example 1 - Cattle and Egret Birds. As the cattle move, they stir up the small insects hiding in the grass and birds feed on it. So, here birds are getting food however cattle are neither harmed nor benefited.
• Example 2 - Remora fish and Shark. Remora attaches itself to the fins of Sharks or Whales and feeds on leftover food and benefit for transportation and protection from predators. In this interaction host organism i.e. shark is neither harmed nor benefited.

Additional Information

1. Mutualism (Positive type of interaction)

• In this type of interaction, both organisms are benefited.
• Example. Association between hermit crab and Sea anemone. Crab carries the Sea anemone to a fresh feeding site and Sea anemone provides protection to crab from enemies (predators).

2. Parasitism (Negative type of interaction)

• In this type of interaction, one species harms the other by making its direct or indirect use for food or shelter.
• A parasite is an organism that lives on or inside the body of another organism and derives its food from it. Harmed organism is called a host and benefitted one is called a parasite.
• Example: Cuscuta, a parasitic plant that is commonly found growing on hedge plants, does not have chlorophyll and leaves for photosynthesis. Hence it derives its nutrition from the host plant which it parasite over other plants.

3. Predation (Negative type of interaction)

• In this type of interaction, one organism kills and feeds on another.
• Predator is the organism that kills and feeds the other and prey is the one who dies or becomes a feed.
• However, predation is an important interaction because it helps to maintain constancy in a number of prey populations and thereby maintaining a balance within an ecosystem.
• Ex. Snake eats a Frog. Here snake is a predator and the frog is a prey. The frog is killed and eaten by a snake and thereby snake is benefitted and the frog is affected.

 

Concept-

• A food chain shows the feeding relationship between different organisms in a particular environment and/or habitat.
• A food chain shows how energy is passed from the sun to producers, from producers to consumers.
• Producers →  Consumers in the series that depicts the correct energy flow in an ecosystem.
• They also show how animals depend on other organisms for food.
• In the food chain energy flows in the form of food.

Explanation-

• Every organism depends on other organisms for food material and all organisms are (producers to consumers) arranged in series in which food energy is transferred through repeated eating and being eaten.
• The green plant in the ecosystem is called producers.
• Producers prepare food from solar energy(sun).
• All the heterotrophs of the ecosystem are known as consumers.
• Consumer, directly and indirectly, depends on the producers for food.

Therefore, the relationship between producers and consumers of different orders is called a food chain.

Additional InformationFood web

• A food web is related to a food chain, but the food web is significantly larger.
• Occasionally, a single organism is eaten by a large number of predators, or it consumes a number of other species.
• As a result, several trophic levels become intertwined, and the food chain fails to accurately depict the flow of resources.
• The food chains are very simple and hence, do not exist in reality,
• Rather, an interconnection of many food chains is seen in nature or in our ecosystem that forms a food web.
• As several trophic levels get intertwined, the energy flow doesn't follow a linear or a unidirectional pattern, rather it is multidirectional or we can say that as, in a food web, one organism takes place at different trophic levels in different food chains (which combine to form a complex food web), the energy flow is multidirectional.

The correct answer is Emerson.

Concept:

• The photosynthetic pigments are organised into two discrete photochemical Light Harvesting Complexes (LHCs) known as Photosystem-I (PS-I) and Photosystem-II (PS-II).
• In Photosystem-I, the reaction centre or chlorophyll-a has peak of absorption at 700nm, known as P700.
• In Photosystem-II, the reaction centre has absorption peak at 680nm hence, called P680.

Explanation:

• Emerson discovered the red drop effect as a result of Photosystem II's photochemical activity being disrupted.
• Because wavelengths beyond 700nm are useless for photosynthesis, a significant drop in efficiency is observed at 700nm.
• This phenomenon of reduced photochemical efficiency at wavelength above 680nm is known as the red drop effect.
• The red drop effect is visible in the red part of the spectrum and results in a decrease in photosynthesis efficiency.
• In other words, after 680nm, the quantum yield decreases.
• The quantum yield is the number of oxygen molecules released per quanta of light.
• This decrease in quantum yield can be seen in the red region of the light spectrum.
• As PS II operates at a wavelength of 680nm, its disruption would mean that only PS I, whose optimum wavelength is 700nm, is operational.
• As a result of the disruption of PS II's photochemical activity, the Red Drop effect is observed.

Important Points

• Emerson also showed that the Emerson Enhancement Effect.
• This phenomenon shows that when red and far-red light is given simultaneously, the quantum yield increases.
• This increased rate of photosynthesis is higher than the sum of the yields of red light and far-red light taken separately.

Additional Information

• Van Niel was a microbiologist who made a significant contribution on the basis of his studies of purple and green sulphur bacteria (photosynthetic bacteria) in understanding photosynthesis.
• Calvin used Chlorella as an experimental material and discovered the first stable product of photosynthesis.

Shorea robusta is used in making railway sleepers.

Key Points

• Shorea robusta is the botanical name of the Sal tree.
• The sal tree is indigenous to India and roughly one-eighth of the total forest area of India is covered by sal trees.
• It is particularly found in the central and northeastern parts of the country up to the Himalayan foothills.
• It is a species of tree in the family Dipterocarpaceae.
• This tree is native to the Indian subcontinent.
• It is a coarse-grained wood that is an important source of timber in India.
• Sal wood is used in making railway sleepers, railway coaches, and furniture because:
• It is very hard, tough and heavy, which is suitable for bearing heavy weight.
• The heartwood is naturally very durable.
• It does not get affected by termites for a long period of time.
• As they are large trees, the wood is suitable for producing beams and poles too.

Additional Information

• Morus alba-
• ​It is commonly called white mulberry or silkworm mulberry.
• It is used as food for silkworm rearing.
• Madhuca indica-
• ​It is commonly known as the mahua tree.
• It is a tropical tree found in the Indian subcontinent.
• It has pharmacological uses as anti-diabetic, anti-inflammatory, etc.​

Concept -

• Charles Darwin made a sea voyage around the world on a ship named H.M.S. Beagle.
• Charles Robert Darwin gave the theory of evolution by natural selection.
• The theory was known as the theory of natural selection.
• He explained the process by which organisms change over time as a result of changes in behavioural traits.
• He proposed this theory in his book “The Origin of Species”.
• He gave an explanation of the formation of new species i.e. various species evolve from single species through adaptation to the environment.
• He is also known as the father of evolution.

Explanation-

• Darwin explained that variations appearing due to environmental changes are transmitted to the next generation.
• So offspring become different from ancestors.
• In the next-generation process of Natural selection repeats so after many generations, a new species is formed.

Therefore the theory of the origin of species by natural selection was given by Charles Darwin.

Additional Information

• The theory of Natural Selection was proposed by Darwin and Wallace.
• The theory of continuity of germplasm by Weismann.
• Evolution term introduced by H. Spencer.

The correct answer is Free-central.

Concept:

• The arrangement of ovules within the ovary is known as placentation.
• The placenta is a tissue, which develops along the inner wall of the ovary.
• The ovule or ovules remain attached to the placenta.

Explanation:

• The gynoecium in the Caryophyllaceae family are syncarpous, i.e., the carpels are fused together.
• However, the styles and stigma remain free from carpel.
• In Caryophyllaceae family ovary is unilocular (only one locule).
• The unilocular ovary shows the Free-central type of placentation.
• Free-central placentation: When the ovules are borne on central axis and septa are absent, the placentation is called free-central.

Thus, In family Caryophyllaceae, placentation is Free-central.

Additional Information

• Parietal placentation:
• It is found in the Brassicaceae family.
• In this type of placentation, the ovules develop on the inner wall of the ovary or on peripheral part.
• Basal placentation:
• ​It is found in the Asteraceae family.
• In this type, the placenta develops at the base of the ovary and a single ovule is attached to it.
• Axile placentation:
• ​It is found in the Solanaceae (potato) family.
• In this type, the placenta is axile and the ovules are attached to it in a multilocular ovary.

The hind wings of houseflies are modified into little halteres. During the flight, these beat faster than fore wings.

Key Points

• The common name of a housefly is Musca domestica.
• It belongs to the order Diptera and genus Musca.
• About 90 percent of all flies occurring in human habitations are houseflies.
• The adult housefly is dull grey with dirty-yellowish areas on the abdomen and longitudinal lines on the thorax.
• Shortened hindwings are called halteres. They are modified hindwings.
• They are present in pairs just at the back of the forewings.
• Halteres are used in balance to help stabilize the housefly in flight.
• Houseflies flap their halters at high speeds during flight.
• If one haltere is removed, the housefly can only fly in circles.
• If both halteres are removed, the fly cannot take flight at all.

Additional Information

• Kingdom Animalia is divided into sub-groups which is known as Phylum. There are 11 phyla in the kingdom Animalia:
• Porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata, Chordata.
• Arthropoda is the largest phylum of Animalia.
• Arthropoda includes insects.

The correct answer is Petrifaction.

Concept:

• Fossilization is defined as the physical, chemical and biological processes that lead to the preservation of plant and animal remains over time.
• Some common methods of fossilization are petrifaction, permineralization, compression, casts and molds.

Key Points

• Petrifaction is the process by which biological material transforms into a fossil by replacing the original material and filling the original pore spaces with minerals.
• The fossils formed as a result of this process typically contain a significant amount of the original material of the specimen.
• Groundwater containing dissolved minerals fills the pore spaces and cavities of specimens, most notably bone, shell, or wood.
• When these minerals precipitate out of the water, they fill the pores of the organisms tissues.
• These are the best, but most rare, types of fossils because they preserve both the external forms and the internal structures.
• The cellular details are preserved due to the infiltration of minerals like MgCO₃, CaCO₃, SiO₂, FeS, etc. into the tissue.

Additional Information

• Pseudofossils: 
• Inorganic rocks that appear to be fossils are sometimes mineral deposition.
• Compression:
• Plant parts such as leaves, stems, and seeds are compressed by the sediments' vertical pressure.
• Flattened plant parts are retained as thin carbonaceous films and the outline of external features.
• Internal structures are generally not preserved.
• Incrustation:
• The deposition of carbonate minerals and iron occurs in the form of a hard cast or incrustation around the plant parts.

The correct answer is Excretory.

Key Points

• Unio is a genus of medium-sized freshwater mussels, aquatic bivalve mollusks (Phylum Mollusca) in the family Unionidae, the River mussels.
• Unio is the type genus of the family Unionidae.

Keber's organ

• It is the excretory organ in certain organisms like molluscs (which includes - Mussels, snail, octopus, clams etc.).
• It is otherwise also called as 'pericardial gland'.
• Keber's organ function is similar to that of the kidney and are present in addition to the kidneys (organ of Bojanus).
• Structure:
• ​It is a large, reddish-brown glandular mass.
• Location:
• It may be over the auricle surface (articular glands), on the pericardium (pericardial glands), or in both positions. i.e., situated antero-lateral to the pericardium into which it discharges the waste material.
• They are collected from that point by the kidney.
• Function:
• The organ is responsible for the removal of nitrogenous wastes.
• The wastes are excreted into pericardium from where these are collected by the 'organ of Bojanus' to be discharged outside the body.
• Pericardial glands of bivalves have revealed that these consist of podocytes where the base of cytoplasmic extensions gives rise to numerous pedicels.
• These form a net with slits through which the fluid is filtered.

Additional Information

Unio: Organs and their function

• Excretory organ: The excretory system of Unio includes a pair of kidneys (organs of Bojanus), a pericardial gland (Keber's organ).
• Vascular: The blood vascular system is well developed and is of open type. It comprises the blood, heart, pericardium, arteries, sinuses, and veins.
• Digestive: The liver is the only digestive gland that surrounds the stomach. It secretes digestive enzymes and its cells are capable of ingesting food particles where intracellular digestion (i.e. digestion occurs in a cell) also occurs.
• Reproductive: In Unio, the sexes are separate (dioecious) but there is no sexual dimorphism.

About Phylum Mollusca

• Mollusks are terrestrial or aquatic (marine or freshwater) animals having a calcareous shell.
• The body is covered by a calcareous shell and is un-segmented with a distinct head, muscular foot, and visceral hump.
• A soft and spongy layer of skin forms a mantle over the visceral hump.

Unio (Fresh-water Mussels)

• It belongs to bivalve molluscs.
• The animal is sedentary and eventually settles down on the bottom of the river or the lake through the mud or sand.

Concept-

• The parasympathetic nervous system is composed mainly of the cranial and spinal nerves.
• The preganglionic neurons, arising from either the brain or sacral spinal cord, synapse(meet) with just a few postganglionic neurons which are located in or near the effector organ (muscle or gland).
• The parasympathetic nervous system is responsible for the body's rest and digestion response when the body is relaxed, resting, or feeding.

Key PointsNerves of the parasympathetic nervous system-

• Nerve fibres of the PSNS arise within the central nervous system. The primary nerves involved are cranial nerves. Below are some of the main cranial nerves in the PSNS:
• Vagus nerve – approximately 75% of all the parasympathetic nerves are vagus nerves. These nerves have branches in many key organs such as the stomach, kidneys, bladder, and reproductive organs.
• Oculomotor nerve – these nerves are able to help constrict the pupils.
• Glossopharyngeal nerve – these nerves project to the salivary glands to provide extra salivation to the tongue

Functions of parasympathetic nervous system-

• Parasympathetic nervous system is able to decrease heart rate, especially when at rest after completing physical exercise or after stressful situations.
• It also stimulates salivation of the mouth to enable the easier digestion of food through the enzymes within saliva.
• Digestion is also promoted within the stomach as well as releasing bile for the body to digest fats.
• The PSNS also contracts the bladder so that urination can occur, in addition to being able to move food within the intestines down the digestive tract to enable bowel movements which is called peristalsis.
• When stressed, the PSNS triggers the necessary responses in order to return to homeostasis (the maintaining of balancing internal physiology).
• Without the PSNS, we may either constantly be in a state of elevated stress response or the regulation of our everyday bodily processes would be dysfunctional, such as being unable to digest food or control our bladder.

Additional Information

• The sympathetic nervous system can:
• accelerate heart rate,
• widen bronchial passages,
• decrease motility of the large intestine,
• constrict blood vessels,
• increase peristalsis in the esophagus,
• cause pupillary dilation,
• piloerection (goose bumps),
• perspiration (sweating),
• raise blood pressure.

Concept-

• Kingdom Plantae is divided into five groups- Algae, Bryophyta, Pteridophyta, Gymnosperm, and Angiosperm.
• Algae
• The plant body is not differentiated from roots, stems, and leaves.
• They are also known as thallophyta.
• Bryophyta
• These are small terrestrial plants.
• They show differentiation in the body design, with stem, leaf-like structures, and root-like structures.
• Pteridophyta
• The plant body is differentiated into roots, stems, and leaves, apart from having a specialized tissue for conduction.
• Gymnosperms
• Gymnosperms are plants with naked seeds.
• Angiosperms
• Angiosperms are seed-bearing plants. Seeds develop inside tissues that get modified to form the fruit of the plant.

Explanation-

• Evolutionarily, Pteridophyta is the first terrestrial plant to possess vascular tissues – xylem and phloem.
• Bryophytes lack vascular tissues.
• They produce a multicellular body called a sporophyte.
• The sporophyte is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it.
• Some cells of the sporophyte undergo reduction division (meiosis) to produce haploid spores.
• All the multicellular eukaryotic plants are autotrophic i.e., they manufacture their food by photosynthesis.
• Oogamous type of sexual reproduction is found in bryophytes.
• As a result of the fertilization, a diploid zygote is formed.
• The zygote does not undergo reduction (meiosis) immediately, but initiates the sporophytic generation.
• Sporophytic generation is a diploid stage.

Therefore, "zygote undergoes meiosis" is the false statement about bryophytes.

The correct answer is Both.

Concept:

• G.H. Hardy and Wilhelm Weinberg independently described the basic principle of population genetics that is known as the Hardy-Weinberg principle.
• Hardy-Weinberg principle states that gene frequency in a population remains stable and constant from generation to generation.
• The gene pool is constant and this is called Hardy-Weinberg equilibrium or genetic equilibrium.
• Gene pool - total number of genes and their alleles in a population.
• It can be expressed by a mathematical equation:

​p² + 2pq + q² = 1

where p and q are frequencies of the dominant and recessive allele respectively.

• This equation can also be used to calculate the genotypic frequencies in a population at equilibrium.
• ​p² - homozygous dominant frequency
• q² - homozygous recessive frequency
• 2pq - heterozygous frequency

Explanation:

• Hardy-Weinberg equilibrium is affected by Mutation, Natural selection, Genetic drift, Genetic recombination and Gene migration or gene flow.

1. Mutation-

• Advantageous mutations lead to new phenotypes and over few generations, result in speciation.

2. Natural selection-

• It is a process in which heritable variations enhance resource utilization for few individuals, enabling them to survive and reproduce better.
• This leads to a change in the characteristics of the population, giving rise to new forms.
• Natural selection can have the following three effects:

1. Stabilizing: Large number of individuals acquire mean character value so peak gets higher and narrower.
2. Directional: Large number of individuals acquire value other than mean character value so peak shifts in one direction.
3. Disruptive: Large number of individuals acquire peripheral character values at both ends of the distribution curve and hence two peaks are formed.

Explanation-

• Auxins refer to a group of plant growth hormones or regulator (PGR).
• Auxin (from Greek ‘auxein’ : to grow) was first isolated from human urine.
• The term ‘auxin’ is applied to the indole-3-acetic acid (IAA), and to other natural and synthetic compounds having certain growth-regulating properties.
• Seedless fruits are called parthenocarpic fruit which can be produced by a spray of auxin(IAA).

Therefore statement 1 is CORRECT.

• Fruits are the results of fertilization, there are a few species in which fruits develop without fertilization. Such fruits are called parthenocarpic fruits.
• Such fruits are seedless.

Therefore statement 2 is CORRECT.

• Gibberellins are another kind of promoter PGR.
• There are more than 100 gibberellins reported from widely different organisms such as fungi and higher plants.
• They are denoted as GA1, GA2, GA3, and so on.
• Gibberellins, Auxin, etc. are effective in producing parthenocarpic fruit.

Therefore statement 3 is INCORRECT.

• Fruits are the results of fertilization, there are a few species in which fruits develop without fertilization. Such fruits are called parthenocarpic fruits.

Therefore statement 4 is CORRECT.

Concept-

• Lichen is the symbiotic association of fungi and algae.
• The algal component is known as photobiont.
• The fungal component is known as mycobiont.
• The photobiont prepare food for fungi i.e. algae are autotrophic.
• The fungal component or mycobiont is involved in:
• Outer covering for protection.
• Attachment to substratum
• Protection against harmful radiations.
• The fungi provide shelter and absorb mineral nutrients and water for their partner i.e. fungi are heterotrophic.
• Reproduction in lichens can be asexual as well as sexual reproduction.
• Lichens are found in habitats like walls, window panes, barren rocks, cooled volcanic larva, tree bark and soil.
• Some examples of lichen are: Parmelia, Cladonia, Cetraria, etc.

Explanation-

• Lichen is an air pollution indicator.
• Lichens are very sensitive to sulfur dioxide.
• And it dies in high levels of sulfur dioxide.
• So lichens are not found in the atmosphere which is polluted.

Therefore lichens are a good indicator of air pollution.

Concept-

• A dental formula is a system for summarizing the number of each type of tooth (incisor, canine, premolar, molar) in each quadrant of the mouth.
• Dental formulae vary between species and may be different for the maxillary and mandibular dentition.

Key Points

• Rabbit teeth are also elodont, meaning that they continually grow throughout the life of the rabbit.
• It has no canines in jaw.
• There is a gap in both the jaws at the location of canines. It is called as diastema.
• The dental formula of the rabbit is as follows: 2( I= 2/1, C=0/0, PM=3/2, M=3/3 ) = 28, where I=incisors, C=canine, P=premolar, M=molar.
• 2 main incisors top and bottom, 2 tiny incisors behind the main top ones, and 22 premolars and molars- each side has 6 on the top and 5 on the bottom.
• The part of the teeth visible from above the gum line is called the clinical crown, while the portion below the surface is the reserve crown.
• The upper incisor has hard enamel on the rostral surface and soft dentin on the lingual surface.
• There is an interesting arrangement of the upper incisor in that the second incisor is behind the first incisor.
• The second incisor is also called the peg tooth.
• At rest, the opposing incisors, premolars, and molars remain in contact.
• While eating, rabbits use the incisors to cut the food using a vertical, chopping motion. Once the food is passed to the cheek teeth (premolars and molars), a rotating horizontal stroke is used to grind the food.
• 

Additional Information The dental formulae of some common mammals are given below:

a) Man & Monkey    $I \frac{2}{2}, C \frac{1}{1}, Pm \frac{2}{2}, M \frac{3}{3}= \frac{2123}{2123}\times 2=32$

b) Rabbit                 $I \frac{2}{1}, C \frac{0}{0}, Pm \frac{3}{2}, M \frac{3}{3}= \frac{2033}{1023}\times 2=28$

c) Cow & Goat        $I \frac{0}{3}, C \frac{0}{1}, Pm \frac{3}{3}, M \frac{3}{3}= \frac{0033}{3133}\times 2=32$

d) Dog                    $I \frac{3}{3}, C \frac{1}{1}, Pm \frac{4}{4}, M \frac{3}{2}= \frac{3142}{3143}\times 2=42$

e) Rat & Mouse      $I \frac{1}{1}, C \frac{0}{0}, Pm \frac{0}{0}, M \frac{3}{3}= \frac{1003}{1003}\times 2=16$

f) Elephant             $I \frac{1}{0}, C \frac{0}{0}, Pm \frac{3}{3}, M \frac{3}{3}= \frac{1033}{0033}\times 2=26$

g) Kangaroo          $I \frac{3}{2}, C \frac{1}{0}, Pm \frac{2}{2}, M \frac{4}{4}= \frac{3124}{3124}\times 2=34$

h) Sheep               $I \frac{0}{3}, C \frac{0}{1}, Pm \frac{3}{3}, M \frac{3}{3}= \frac{0033}{3133}\times 2=32$

The correct answer is Asterias.

Concept:

• Filter feeders are feeding animals that extract suspended matter and food particles from water by passing it through a specialized filtering structure (gills).
• Filter feeding is the characteristic feature of certain animals known as filter feeders.
• Some animals like Unio, sponges, Amphioxus, Herdmania and many fishes use this feature.

Explanation:

• Unio-
• Unio belongs to the phylum Mollusca.
• Molluscs are filter feeders, and their gill plates trap phytoplanktons.
• Water enters the mantle cavity through an opening and rises through the gills to the suprabranchial chamber.
• Amphioxus-
• Amphioxus belongs to the phylum Chordata and subphylum Cephalochordata.
• In Amphioxus slits are modified to form gills, that extracts food particles from the water in which the animals live.
• Herdmania-
• Herdmania belongs to the phylum Chordata and subphylum Urochordata.
• Herdmania is a filter-feeding tunicate that lives in marine environments.
• Asterias-
• Asterias belongs to the phylum Echinodermata.
• In Asterias specialized filtering structures (gills) are absent.
• So, Asterias is not a filter-feeder.

The correct answer is Axon.

• Nodes of Ranvier are found in (Axon) myelinated nerve fibre.
• A neuron is a microscopic structure composed of three major parts i.e., Cell body, dendrites and axon.
• Axon- 
• Axon is a single, usually very long process of uniform thickness.
• The part of cyton from where the axon arises are called axon hillock (most sensitive part of neuron).
• Axon does not have Nissl's granules, cell organelles and granular bodies.
• The axon transmits nerve impulses away from the cell body to a synapse or to a neuromuscular junction.

Axon are of two types:

1. Myelinated nerve-fibre

• In Myelinated nerve-fibres, Schwann cells form myelin sheath around the axon.
• The gaps between two adjacent myelin sheaths are called nodes of Ranvier.
• Myelinated nerve-fibres are found in cranial, spinal nerves and white matter of brain.

2. Non-myelinated nerve-fibre

• ​In Non-myelinated nerve-fibres, Schwann cells do not form myelin sheath around the axon and are without nodes of Ranvier.
• They are commonly found in autonomic and somatic neural systems.

Thus, Node of Ranvier are found on Axon.

Concept-

• Soil is the uppermost layer of the earth's crust.
• It is a mixture of living or nonliving materials.
• The formation of soils is done by weathering of material (which includes sediments, rocks, etc.) that are deposited by the water bodies near their shore.
• Soils are mainly classified into:
• ​Zonal - These are matured soil types that have developed over a long period of time under good drainage conditions.
• Azonal - They do not have well-developed soil horizons but have uniformity of soil from top to bottom.
• Intrazonal - These are formed in waterlogged areas and may have high content of soluble salts.

Important Points

• Alluvial soils are very fertile because it contains silt and sand carried by the water of rivers.
• It is usually most extensive in the lower part of a river's course, forming floodplains and deltas, but they may form at any point where the river overflows.
• One of the major characteristic of alluvial soil is that it is made by the deposition of the river load as it flows from its upper to its lower.
• On the basis of its ages alluvial soil is divided into Bhangar (Old alluvium) and Khadar (New alluvium).
• It is porous as well as light, so it is easily tillable.
• Alluvial soils are formed mainly due to silt deposited by Indo-Gangetic-Brahmaputra rivers (transported or azonal soils).
• Hence, alluvial soil is a recently formed soil.

Therefore alluvial soil is a type of azonal soil.

Additional InformationZonal soil

• Zonal soil is a major soil group often classified as a category of the highest rank and generally covering a wide geographic region or zone and embracing soils that are well-developed from the parent material by the normal soil-forming action of climate and living organisms.

Intrazonal soil

• These types of soils are intrazonal soils that develop from parent material and are highly rich in lime.
• The soil develops in sub-humid tropics and is very fertile.

Concept-

• Coffea arabica, also known as the Arabian coffee, is a species of flowering plant in the madder family Rubiaceae.
• Coffea arabica is itself the result of a hybridization between the Coffea canephora and Coffea eugenioides.

Key Points

• Rubiaceae, the madder family (order Gentianales) of flowering plants consists of 611 genera with more than 13,150 species of herbs, shrubs, and trees.
• It is distributed primarily in tropical areas of the world.
• Members of the family have leaves opposite each other with stipules or in whorls, unbroken leaf margins, and leaflike appendages at the base of the leafstalks.
• Plants may bear a single flower or many small flowers clustered together.
• Much branched tap root system.
• Inflorescence found is dichasial cymes, sometimes aggregated into heads.

Important Points

• C. arabica is mostly cultivated in Latin America.
• Arabica coffee is considered a mild, aromatic brew that is more flavourful than the other varieties.
• Arabica and Robusta are two major coffee varieties, which are obtained from C. arabica and C. canephora respectively.

Additional Information

• Apocynaceae-
• Apocynaceae is a family of trees, shrubs or sometimes herbs usually with milky sap, that comprises about 200 genera and 2,000 species.
• The leaves are simple, usually opposite and decussate, or whorled, while stipules are usually absent.
• The flowers are bisexual and actinomorphic or sometimes weakly zygomorphic.
• Acanthaceae-
• These have simple leaves arranged in opposite pairs, with cystoliths (enlarged cells containing crystals of calcium carbonate) in streaks or protuberances in the vegetative parts.
• The bisexual flowers are frequently bilaterally symmetrical and are usually enclosed by leaflike bracts, often coloured and large.
• Solanaceae-
• They have taproot system.
• The stem is either erect or climber.
• It includes herbs, shrubs, small trees, and climbers.
• The leaves are alternate, simple or pinnately compound (rarely); exstipulate with reticulate venation.

The correct answer is A. R. Wallace.

Key Points

• Zoogeography is the "study of the geographic distribution of animals".
• It is the science whose primary aim is to identify, describe, and explain the distribution of both land and aquatic species of animals in the different regions and localities of the earth.
• The concept was originated by naturalists like A. R. Wallace in the 19th century.
• The faunal regions are mostly described on the basis of vertebrate fauna, including invertebrates only at times.
• It was also shown as evidence of continental drift and how migration of species took place from their centers of origin.
• Each region more or less coincides with a major continental land mass separated by oceans, deserts or mountain ranges.

Important Points

• There are 7 zoogeographic regions:
• Palearctic - comprises Europe and Asia from north of the tropics.
• Ethiopian - comprises of Africa south of the Sahara desert and parts of southern Arabia.
• Oriental - includes tropical Asia and associated continental islands.
• Nearctic - consists of North America except for tropical Mexico.
• Neotropical - comprises South and Central America including Mexico.
• Australian - covers Australia and New Guinea.
• Antarctic - essentially covers the Antarctica continent.

Additional Information

Table : Scientist & their discoveries

The correct answer is DPD.

Concept:

• Diffusion is a movement of substances from the region of their high concentration to the region of their lower concentration.
• The diffusion process is an important phenomenon in plants as it is the only means of the transport of the gases and materials in them.

Explanation:

Diffusion pressure deficit (DPD)

• Diffusion pressure deficit (DPD) is the force that determines the flow of water from one cell to the another.
• It is the difference in diffusion pressure between two solutions.
• It is the amount by which the diffusion pressure of water or solvent in a solution is less than the diffusion pressure of pure water or solvent.
• Because of the diffusion pressure gradient, it allows for easy water absorption. Water flows from low to high Diffusion pressure deficit.
• DPD = Osmotic Pressure - Turgor Pressure

Important Points

• DPD in a plant is an important parameter as it defines how much water a cell can take up.
• For a turgid cell, DPD is zero.
• Whereas, it will be highest for a plasmolyzed cell.

Additional Information

• Osmotic pressure (OP)
• It is defined as the amount of pressure which must be applied in order to prevent the passage of solvent due to osmosis.
• Water potential (WP)
• The difference between the free energy of water molecules in pure water and the energy of water in any other system is known as water potential.
• Turgor pressure (TP)
• When water enters a plant cell through diffusion, it becomes turgid due to building up of pressure against the cell wall in a plant system, this pressure is known as turgor pressure.

The correct answer is Theobroma cacao.

Key Points

Theobroma cacao, also called the Cacao tree and the cocoa tree, is a small evergreen tree in the Family Malvaceae (Family of Hibiscus i.e. Shoe Flower),

• Native: It is native to the Amazon basin, Central and South America.
• Seeds: About 20-60 seeds are contained in the pod of a single cacao fruit.
• Commercial use: Cocoa are seeds obtained which are then processed to make chocolate, chocolate liquor, cocoa solids, cocoa butter and other such variants.

Figure. Process of Chocolate Making from Cocoa Beans

Additional Information

Concept:

• Jean-Baptiste Lamarck was a French biologist who was one of the first to propose biological evolution.
• His theory is called Lamarckism and is based on two basic principles:
• Inheritance of acquired characters
• Use and disuse of organs during the lifetime of an organism.
• He proposed that changes in environment necessitates new needs in organism.
• This leads to new uses of pre-existing features or disuse of pre-existing features, causing a physical change in the features.
• He also stated that these changes were then acquired by the offspring in the next generation.
• The theory was explained with the example of giraffe.
• It was stated the giraffe ancestors stretched their necks to reach out to the leaves on higher branches of a tree.
• The ones with longer neck were more successful in getting food and produced offspring with longer necks.

Key Points

• Lamarck's "acquired trait theory" was challenged by August Weismann.
• Weismann conducted rat tail clipping and dissemination experiments for several generations.
• He cut off the tails of mice over several generations without creating tailless types.
• He believed that this was evidence against the inheritance theory of acquired traits.
• Weismann was able to show the inadequacy of much of the evidence generally accepted by Lamarckism.
• He also pointed out that germplasm continuity is sufficient to explain the inheritance of majority of the traits common to all **individuals. **​

Additional Information

• Charles Darwin -
• Charles Darwin was an English naturalist and biologist who went on the famous voyage of H.M.S Beagle.
• ​He is known for writing the book 'On the Origin of Species' in which he explained the theory of evolution by natural selection as 'descent with modification'.
• He gave the 'theory of natural selection' and the concept of 'survival of the fittest' as mechanisms of evolution.
• Hugo de Vries -
• ​Hugo de Vries was a botanist and geneticist, known for his mutation theory of evolution.
• He suggested that speciation (evolution of species) occurs due to sudden large changes in traits rather than small gradual changes, as was previously suggested by Darwin.
• H. Spencer -
• ​Herbert Spencer was a philosopher, anthropologist, biologist who is known for his hypothesis on social Darwinism.
• He stated that social evolution takes place much like biological evolution where the same principles of natural selection and ‘survival of the fittest’ can be applied.

The correct answer is Lophotrichous.

Concept:

• Flagella : It is a slender threadlike structure, especially a microscopic part that enables many protozoa, bacteria, spermatozoa, etc. to swim.
• Parts of flagella : Bacterial flagellum is composed of three parts – filament, hook and the basal body.

Explanation:

Based on the number and placement of flagella on the cell, there are four types of flagellar arrangements. They are -  

 

Additional Information

• Based on the shape, Bacterias are categorized into - 
• Cocci (Round shaped bacteria)
• Bacilli (Rod-shaped bacteria),
• Cocco-bacilli (combination of Round-Rod shaped bacteria),
• Spirilla (Spiral-shaped bacteria).
• Vibrio (Comma-shaped bacteria),
• Spirochete (Slender spiral-shaped bacteria).

The correct answer is Archaebacteria.

Key Points

• Methanogenic bacteria belong to the Kingdom Archaebacteria, which is now known as the domain Archaea.
• Methanogens bacteria are a single-celled organism.
• Methanogenic bacteria are primitive prokaryotes as they lack well-defined cell nuclei.
• These bacteria are anaerobic.
• They live anaerobically in swamps, marshes and in the guts of several ruminants such as cows, buffaloes, goats, etc.
• They live as symbionts in the rumen (first part of stomach) of herbivorous animals that chew their cud (example cow, buffalo, goat, etc.).
• These bacteria also help in the digestion of cellulose in ruminants.
• These bacteria have been exploited for the production of methane-rich gobar gas or biogas from the dung of these animals.
• The fermentation of cattle dung by methanogens is done in specially designed gobar gas plants.
• It not only provide cooking gas (fuel gas), but also leaves behind a slurry which can be used as an organic matter for growing crops.
• They produce almost 65% of atmospheric methane.

Additional Information

• Mycoplasma -
• It is genus of bacteria that lack cell wall.
• It is placed under the domain Bacteria.
• Eubacteria -
• They refer to the "true bacteria" which have a rigid cell wall.
• They are single-celled prokaryotic organisms.
• Cyanobacteria -
• They refer to a phylum of bacteria that can perform photosynthesis.
• They were previously placed under Cyanophyta as an algal group.
• Hence, they are also sometimes referred as blue-green algae.

The correct answer is Archegonium.

Key Points

• Archegonium is the female reproductive organ found in ferns and mosses.
• Archegonium is flask-shaped and produces a single egg.
• At maturity, the archegonium consists of two parts - basally swollen part venter and a slender long neck.
• The male reproductive organ is called the Antheridium, which produce biflagellate antherozoids.
• The antherozoids are released into the water where they come in contact with archegonium. An antherozoid fuses with the egg to produce the zygote.
• The zygote do not undergo reduction division immediately.
• The zygote develops into the multicellular embryo within the archegonium.
• This is known as the sporophyte.

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Additional Information

Moss: General characteristics 

• Mosses and liverworts are plants that belong to Phylum Bryophytes and include various plants that are found commonly growing in moist shaded areas in the hills.
• They are amphibious plants that can live in soil but are dependent on water for sexual reproduction.
• It is thallus-like and prostrate or erect and attached to the substratum by unicellular or multicellular rhizoids.
• They may possess root-like, leaf-like or stem-like structures
• The main plant body of the bryophyte is a haploid. It produces gametes, hence is called a gametophyte.
• The sex organs in bryophytes are multicellular.
• The sporophyte is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it.
• Reproductive organs
• Antheridium - It is a male sex organ in Moss, fern, fungi, and non-flowering plants.
• Oogonium - It is the female sex organ of certain algae and fungi, typically a rounded cell or sac containing one or more spores.

The correct answer is Phytomastigophora.

Concept:

• Euglena is a single-celled eukaryote placed under Kingdom Protista.
• They are primarily aquatic organisms.
• The cell body of Protistans contains a well-defined nucleus and other membrane-bound organelles.
• Some have flagella or cilia.
• Protists reproduce asexually and sexually by a process involving cell fusion and zygote formation.
• Euglena contains chloroplasts or chromatophores that bear the pigments.
• They contain the green pigment chlorophylls a and b as well as β-carotene pigment.
• The chloroplasts are slender, elongated and band-like structures present in the endoplasm of cell.

Key Points

According to the locomotive organs, Protozoans are classified into 4 classes -  

1. Mastigophora (Flagellates) -

• This class is classified into -

1. Phytomastigophora
2. Zoomastigophora
3. Sarcodina (Amoeboids) -

• They move using pseudopodia or false legs, which are an extension of the cytoplasm.
• The most common example is Amoeba.
• This class is further divided into -

1. Rhizopoda
2. Phyrophasmida
3. Actinopoda
4. Sporozoa (Non-motile) -

• This Class is further divided into - Teleospora, Taxoplasmea, Haplosporea

4. Ciliophora (Cilliates) - 

• This Class is further divided into class - Cilliatae

Important Points

• Phytomastigophora :
• These are pigmented, aquatic and covered by an exoskeleton of calcium.
• These are autotrophic and perform photosynthesis.
• Examples- Chlamydomonas, Euglena, and Volvox.
• Zoomastigophora:
• They are found as symbionts or parasites.
• Some organisms are found in marine habitats.
• Examples- Leishmania, & Trypanosoma.
• Rhizopoda:
• It is a large group of Protista.
• They capture prey using pseudopodia.
• They are heterotrophic.
• Example- Entamoeba histolytica.
• Actinopoda:
• ​They have shells (exoskeleton) made up of silica.
• Pseudopodia are needle-like.
• Examples- Radiolarians, Actinosphaerium.

Therefore, Euglena belongs to Phytomastigophora.

The correct answer is Allium.Concept:

• Embryo-sac is the oval structure present in the ovule of flowering plants, which is also the female gametophyte.
• The female gametophyte of a flowering plant, which develops within the ovule, is protected by the nucellus and the integuments of the ovule.
• It typically consists of an egg cell, a central cell, 2 synergids and 2 antipodal cells.
• An embryo sac is said to form when the haploid megaspore nucleus divides. It possesses 8 haploid nuclei and 7 haploid cells which do not have cell walls.
• At the event of fertilization, one male nucleus and egg nucleus combine for the formation of zygote leading to the development of the embryo.
• Endosperm forms with the triple fusion of the 2 polar nuclei and the second male nucleus.

Key Points

• Megasporogenesis is the process by which megaspores are formed from the megaspore mother cell (MMC) by meiosis.
• After meiosis, the megaspores may develop into embryo sac by different methods, which is characteristic of each plant.

Formation of Embryo Sac:

1. Monosporic or Polygonum-type embryo sac (Most common type of embryo sac):

• In this type, meiosis of the diploid megaspore mother cell in the nucellus produces four haploid megaspores as a megaspore tetrad.
• Three of the megaspores, usually those at the micropylar end of the nucellus, subsequently undergo programmed cell death, leaving only one functional megaspore.
• A single functional megaspore differentiates towards micropylar end with two haploid nuclei.

2. Bisporic Embryosac:

• In this type, meiosis produces only two megaspores, each containing two haploid (n) nuclei as a diad.
• This is due to the absence of cytokinesis (division of cytoplasm) and cell plate formation following the second meiotic division.
• It is commonly found in Allium.

3. Tetrasporic Embryo sac:

• In this type of embryo sacs, cell plates fail to form after both meiotic divisions, resulting in a single four-nucleate megaspore.

All three patterns give rise to a single functional megaspore that contains either one (monosporic), two (bisporic), or four (tetrasporic) haploid nuclei.

Concept-

• Steroid hormones, such as testosterone, are hydrophobic molecules that diffuse freely into and act within all cells.
• Therefore, there is no need for a receptor bound to the cell membrane, instead, there is a mobile receptor protein in the cytoplasm.

Key Points

• Testosterone can easily cross cell membranes.
• Cells do not need to invest in a trans-membrane delivery system if they can do the same for their intracellular receptors.
• The signal gain may be lower (shorter signal steps mean fewer gain steps).
• This means that the signalling pathway is less sensitive and/or slower, but is ideal for transmitting hormonal signals where transmission speed and specificity (in terms of precise location) are not very important.
• It is intended to affect systems in the most cost-effective way at the right time.

Additional InformationTSH

• TSH binds to the thyroid hormone (TR) receptor, a member of the nuclear hormone receptor family.
• TR acts as a ligand-activated transcription factor that binds to the cognate thyroid hormone response element (TRE) in the promoter of the target gene.

PTH

• The receptor binds to parathyroid hormone and belongs to the GPCR family of transmembrane proteins.
• The parathyroid hormone 1 receptor (PTH1R) is a classical PTH receptor that is expressed at high levels in bone and kidney and modulates calcium ion homeostasis by activating adenylic acid cyclase and phospholipase C.

FSH

• Follicle Stimulating Hormone (FSH), a glycoprotein hormone. , an essential component of the endocrine system that regulates gonad function and fertility.
• FSH must bind to a receptor (FSHR) on Sertoli cells of the testis and granulosa cells of the ovary to transmit a signal.

Concept-

• A tadpole is a larval stage in the life cycle of an amphibian.
• Most tadpoles are fully aquatic, though some species of amphibians have tadpoles that are terrestrial.

Key Points Structure of a freshly hatched tadpole larva:

• A freshly hatched tadpole larva has a limbless body.
• The body is divided into an ovoid head, a short trunk and a slender tail.
• A small opening situated ventrally at the root of the tail is known as the anus.
• An adhesive sucker is present on the ven­tral side of the head by which the tadpole larva attaches itself to the aquatic weeds.
• The mouth is lacking and as a result, it cannot take anything from outside.
• The yolk material provides the nutrition.
• The respiratory organs comprise three pairs of highly vascular and branched feathery external gills.
• After a few days the mouth is formed near the sucker.
• A pair of horny jaws surround the mouth.
• The tail becomes more elongated and develops a dorsal and a ventral fin.
• V­-shaped myotomes develop on both sides of the tail.

Concept-

• The theory of evolution by natural selection was proposed by Charles Darwin.
• It stated that all life forms arise due to natural selection of small inheritable changes that increase the survivability of a species.
• Darwin also defined evolution as descent with modification, meaning we have evolved from our ancestors through inheritable variations of characteristics.
• The evidences for evolution include:
• Paleontological Evidence - Study of fossils have revealed that different life forms existed in different geological time-periods and similarities exist between existing and pre-existing life forms.
• Anthropogenic Evidence - Overuse of pesticides and herbicides have resulted in natural selection of resistant varieties in much lesser time.
• Comparative Anatomy & Morphology - Homology and analogy are based on comparisons between structure and functions of organs that show evolutionary adaptations in nature.

Key Points

• Homologous structures refer to the similar structures that differ in functions.
• Example - Forelimbs of whale, bat, cheetah and human.
• They are all made of humerus, radius, ulna, carpels, metacarpels and phalanges.
• Flippers of whales are used for swimming, wings of bats for flying and forelimbs of man for grasping and forelimbs of cheetah for running.
• Homology indicates divergent evolution -
• The same structure evolved in different directions.
• This shows evolutionary adaptations due to varying needs.
• Divergent evolution leads to speciation and works on the premise that there is a variety inside the quality pool of a population.
• It also indicates common ancestry - 
• The functions diverged from a common ancestor.
• Example - Thorns of Bougainvillea and tendrils of Cucurbita are both modified branches.

Additional Information Convergent evolution

• Convergent evolution happens when species have comparable environmental conditions to which they adjust to in comparable ways.
• It is evident for analogous structures.
• Analogous structures refer to different structures with similar functions.
• Example- Sweet potato and potato are root and stem modifications respectively but both function as storage organ.

Macroevolution and microevolution

• Microevolution is the process by which organisms changes in small evolutionary ways over a long time.
• Macroevolution refers to larger evolutionary changes that result in new species.

The correct answer is Palaearctic.

Key Points

• Zoogeography refers to the geographic distribution of animal life or fauna.
• The concept was originated by naturalists like A. R. Wallace in the 19th century.
• The faunal regions are mostly described on the basis of vertebrate fauna, including invertebrates only at times.
• It was also shown as evidence of continental drift and how migration of species took place from their centers of origin.
• Each region more or less coincides with a major continental land mass separated by oceans, deserts or mountain ranges.
• Earth is broadly divided into 3 realms - Megagea, Neogea and Notogea.
• These realms are again divided into several regions.
• The classification of land masses into regions, based on studies of Wallace (1876) and Darlington(1957), is given below:

• Thus, Palaearctic is a region in Megagea realm.
• Hence, the Palaearctic is not the zoogeographic realm.

Concept:

• Thallus is a plant body that is not divided into stems and leaves and has no roots or vascular system.
• Thalli are found in algae, fungi, lichens and some liverworts.
• It may be unicellular or complex tree-like structures.
• These thalli may develop into reproductive structures called fruiting bodies in fungi.

Key Points

Holocarpic-

• This is a rather spherical unicellular structure in some subspecies of fungi such as Chytrids.
• On maturation, the entire thallus becomes a reproductive structure.
• Thalli with this structure are called a holocarpic thallus.
• The entire thallus functions as a sporangium.
• Example - Synchitrium.

Additional Information

• Eucarpic: It is a thallus in which only a part of it differentiates to form reproductive or structures. Most of the fungi are eucarpic.
• Holozoic: It is a type of nutrition in which liquid or solid organic matter is ingested, digested, absorbed, and assimilated. It requires the conversion of complex substances into simple substances. Example - Humans take food inside its body by ingestion and then it is digested.
• Homothallic: Homothallic means that the male and female reproductive organs are located on the same plant body. It is found in some fungi where opposite sexual functions are performed by different cells of the same mycelium.

The correct answer is Its body cavity is well developed.

Concept:

• Hirudinaria (Indian leech) belongs to the phylum Annelida of Kingdom Animalia.
• Indian leech is the common name of Hirudinaria.
• It inhabits freshwater ponds and still waters near streams and rivers.

Important Points

• Its medical use in India dates back to around 1000 BC: TRUE
• Leeches were used since the time of ancient Egypt to treat infections, skin problems, etc.
• In India, H. granulosa has been used in traditionally for therapeutic purposes.
• It sucks blood from fish, frog, cattles and humans: TRUE
• ​​​It is sanguivorous, i.e., feeds on blood.
• It sucks blood from fish, frog, cattles and humans.
• And single meal can last for over a year.
• Digestion of the blood takes 10 to 14 months: TRUE
• In Hirudinaria, digestion tract is straight and complete, starting from the mouth and ending at anus.
• They usually feed once in every 6 months.
• Presence of some bacteria keep the blood from decaying during the long digestion process.
• Thus, digestion of the blood takes 10 to 14 months.
• Its body cavity is well developed: NOT TRUE
• Hirudinaria (Indian leech) lacks head and parapodia.
• Coelom is greatly reduced by the formation of peculiar connective tissue called botryoidal tissue.
• So, the body cavity is not well developed.

Thus, the statement "Its body cavity is well developed" is not true about the Indian leech, Hirudinaria.

The correct answer is Pisum sativum.

Key Points

• Johann Gregor Mendel is considered as the Father of Genetics.
• He conducted hybridization experiments on garden peas for seven years (1856-1863) and proposed the laws of inheritance in living organisms.
• The factors, now known as genes, are responsible for transfer of characteristics from one generation to another.
• Genetics is the science which deals with the inheritance, as well as the variation of characters from parents to offspring.
• Inheritance is the process by which characters are passed on from parent to progeny; it is the basis of heredity.
• This simply means that due to inheritance, the members of the same family possess similar characteristics.
• Variation is the degree by which progeny differ from their parents or to put in simple words, it refers to the differences among individuals of the same species.

Mendel's experiment in short

• Mendel conducted artificial pollination/cross-pollination experiments using several true-breeding pea lines.
• He selected 14 true-breeding pea plant varieties, as pairs which were similar except for one character with contrasting traits like - smooth or wrinkled seeds, yellow or green seeds, inflated (full) or constricted green or yellow pods and tall or dwarf plants.
• The genetic makeup of the plant is known as the genotype. On the contrary, the physical appearance of the plant is known as phenotype.
• The genes are transferred from one generation (parent) to the another (offspring) in pairs known as allele (variant form of genes).

Explanation:

• Pisum sativum was selected by Mendel because:
• It is an annual plant, therefore, many generations can be studied within a short period of time.
• The pea plant can be easily grown and maintained.
• It is a naturally self-pollinating but can also be cross-pollinated.
• It has several contrasting characters.

Additional Information

1. Gallus gallus domesticus (Andulusian Fowl) 

• It is one of the breeds of domestic chicken, also known as the Blue Andalusian.
• They are either black, blue, or white-feathered.
• The Andalusian fowl reveals the heritage of mixing.
• The cross is made between the black and white feathers of the fowls in this breed of the Andalusian fowl. The blue feathered fowl is the product obtained from the cross.

2. Oenothera lamarkiana (Evening primerose)

• This plant is originally native to Brazil, but has become naturalized in many countries and planted as an ornamental plant in gardens.
• De Vries conducted experiment on Oenothera lamarckiana or Evening Primrose plant.
• It is a self-pollinated plant and its seeds were allowed to grow, the majority of F1 plants were similar to the parents, but a few were different plants.
• The same results were found in the F2 generation.
• Later on, it was revealed that most of the variants isolated from Oenothera lamarckiana were due to its anomalous chromosome behaviour.
• The chromosomes form multiple rings at meiosis and chromosomal end segments only involves in recombination (low-level crossing over) and plant shows complex heterozygosity i.e., during meiosis maternal and paternal chromosomes are arranged in alternate order.

3. Drosophila melanogaster (Fruit fly) 

• The phenomenon of linkage was studied by the scientist T.H. Morgan using the common fruit fly or Drosophila melanogaster.
• Linkage and recombination are phenomena that describe the inheritance of genes.
• A linkage is a phenomenon where two or more linked genes are always inherited together in the same combination for more than two generations.
• Morgan performed a cross between a heterozygous red-eyed female with a white-eyed male. This gave a ratio of 1:1:1:1 in the progeny (1 white eyed female, 1 red eyed female, 1 white eyed male and 1 red eyed male).
• He performed many such crosses and came to the determination that the gene responsible for the eye color was situated on the X chromosome (one of the two sex chromosomes).

Key Points

• Globular proteins are named such for their spherical shapes.
• They are the most abundant proteins of all.
• They are formed of polypeptides like other proteins but are folded into tertiary structures.
• They may form a variety of structures containing α-helices and β-sheets folded into 3D structures.
• This gives them a roundish structure which gains stability by the intrachain bonds.
• They are usually water-soluble because of the hydrophilic amino acid side chains that lie on the surface.
• The diversity of the structures help them to perform diverse functions in organisms.

Explanation:

• Most of the enzymes are globular proteins which have specific functions because of their tertiary structures.
• They can also act as hormones. Example- Insulin hormone.
• Antibodies belong to a group of globular proteins called immunoglobulins. Example- IgA, IgE.
• Haemoglobin is another globular protein present in the blood that helps to bind and transport oxygen in the body.
• But globular proteins do not function as structural molecules.
• The fibrous proteins, which have a linear structure, function as structural proteins. Example- Keratin in hair and nails.

The correct answer is Both (A) & (B).

Concept:

• Inflorescence: Some flowers bloom in bunches while some others bloom vertically**.** This arrangement of flowers on the floral axis (stem) of flowering plants in biology is called Inflorescence. 
• Floral axis is a part of flower on which reproductive organs and other parts of flower are attached).
• Types of Inflorescence: Depending on whether the apex gets converted into a flower or continues to grow, two major types of inflorescences are defined as:
• Racemose - The peduncle grows indefinitely and bears flowers in acropetal order.
• Cymose - The main axis stops growing and terminates in a flower which are formed in basipetal order.
• Acropetal means having the younger flowers at the apex, while basipetal means having the older ones near the apex.

Important Points

• Dichasial cyme Inflorescence (A type of Cymose inflorescence)
• Here, the peduncle (a stalk of flower) ends in a flower, and from the basal part of it, two lateral branches arise, hence has limited growth.
• The flowers are borne in a basipetal order.
• These also end in a flower and this same arrangement occurs on these lateral branches.
• It is usually seen in Solanaceae Family. Ex. Jasmine, Teak, Bougainvillea.

​

• Verticillaster Inflorescence (A type of Cymose inflorescence)​
• In this type, there is a cluster of sessile or subsessile flowers borne on a dichasial cyme ending in monochasial cyme in the form of condensed whorl on either side of the node.
• It is seen in Labiatae / Lamiaceae Family.
• Example: Ocimum (Tulsi), Mint, Coleus, Mustard etc.

​

Lamiaceae family plants like Tulsi (Ocimum sanctum) exhibits mixed inflorescence, i.e. both Verticillaster & dichasial cyme type of inflorescence.

Concept-

A population is defined as a group of individuals of the same species living and interbreeding within a given area.

Key Points Deme-

• A deme is a sub-population (a smaller group within the population) that can freely interbreed.
• Population is usually made of several demes (groups) that are partially isolated from each other.
• Often a geographical barrier limits gene flow between demes, but not sufficiently to result in speciation.
• The deme usually is not a closed population but contributes individuals to neighbouring populations and receives immigrants from them.

Additional InformationCloning- Cloning is the production of a population of genetically identical cells or of organisms asexually produced by a single cell or organism. Cloning is fundamental to most living things, since the body cells of plants and animals are clones that come from a single fertilized egg.

Hybrid- a plant or animal that has been produced from two different types of plant or animal.

Niche- Niche is used to describe the role an organism or population plays within its community or ecosystem.

Concept-

• Ribosomal RNA or rRNA molecules are synthesized in a specialized region of the cell nucleus called the nucleolus, which appears as a dense region within the nucleus and contains genes encoding rRNA.

Key Points

• Ribosomal RNA (rRNA) is a molecule in cells that is part of protein-building organelles called ribosomes and is exported to the cytoplasm to help translate the information contained in messenger RNA (mRNA) to proteins.
• The encoded rRNAs are of different sizes, differentiated into large or small. Each ribosome contains at least 1 large rRNA and at least 1 small rRNA.
• In the nucleolus, large and small rRNAs combine with ribosomal proteins to form large and small ribosomal subunits (eg, 50S and 30S in bacteria, respectively).
• These subunits are usually named for their settling rate, measured in Svedberg [S] units, in the centrifugal field.
• Ribosomal proteins are synthesized in the cytoplasm and transported to the nucleus to be reassembled in the nucleus.
• The subunits are then returned to the cytoplasm for final assembly.
• Prokaryotes have 70S ribosomes that has 50S and 30S subunits, while eukaryotes have 80S ribosome which has a 60S and a 40S subunit.

Additional Information

Protein

• These are the products formed from the genetic information present in a cell.
• They help in carrying out the various metabolic activities of the cell to sustain life.
• mRNA is converted into a protein by the process of translation.

Messenger RNA

• ​This type of RNA functions by transferring the genetic material into the ribosomes and passing the instructions about the type of proteins, required by the body cells.
• We can also say Information from the nucleus to the cytoplasm is carried by m-RNA.
• Based on the functions, this type of RNA is called messenger RNA.
• Therefore, the mRNA plays a vital role in the process of transcription or during the protein synthesis process.

Transfer RNA

• These are RNA molecules that transfers amino acids to the ribosome complex during protein synthesis process.
• Each tRNA carries an amino acid at one end and has an anticodon sequence at another end, which can bind to its complementary sequence on the mRNA.
• Thus tRNAs are adapter molecules that help in reading the genetic code on the mRNA and accordingly add amino acid to the growing peptide chain.
• These are specific for each amino acid.

Concept-

• Growth in plants takes place in two ways:
• Primary growth - It is the main form of growth in a plant that mostly occurs due to activity of apical meristems.
• Secondary growth - This is found in most dicot plants exhibiting an increase in girth.
• Secondary growth is caused by 2 lateral meristems:
• Vascular Cambium - It is responsible for forming secondary xylem and secondary phloem.
• Cork Cambium - It forms the periderm (bark) towards the outer periphery in older plants.
• The cork cambium is also known as the phellogen.

Key Points

• The cork cambium is a type of meristematic tissue present in many vascular plants.
• It usually develops in the cortex region as the stem grows in girth.
• Between the cork and primary phloem, it is one of the several layers of bark. Cork cambium is a lateral meristem that is responsible for secondary growth in roots and stems.
• It can be found in a variety of woody and herbaceous dicots, gymnosperms, and monocots (monocots lack secondary growth).
• The phellogen can be a couple of layers thick and made up of narrow, thin-walled, rectangular cells.
• It can cut off cells on both sides, producing outer and inner cells.
• The outer cells differentiate into the cork or phellem and the inner cells differentiate into the secondary cortex or phelloderm.
• The phellem is impervious to water because of suberin depositions in its cell walls, while phelloderm cells are parenchymatous.
• Phellem, phellogen and phelloderm are together called as the periderm.
• The phellogen may sometimes also form lenticels on the outer surface of the bark through which gaseous exchange may take place.

Additional Information

• The Secondary cortex is a cellulosic cell walled parenchyma cell with a thin wall. Cork and cambium make up the material.
• Cork is an impermeable material, the phellem layer of bark tissues. Cork is composed of suberin, a hydrophobic substance.

The correct answer is D-amino acid.

Explanation:

• Proteins (“proteios” which means - prime importance) are building blocks of all living organism and are the major structural component of cells and is responsible for the building and repair of body tissues.
• All proteins are polymers made up of amino acids. Amino acids contain Amino (–NH₂) and Carboxyl (–COOH) functional groups.
• Amino acids are compounds made up of Carbon (C), Hydrogen (H), Nitrogen (N), and Oxygen (O).
• Some amino acids like methionine and cysteine sometimes contain a small amount of Sulfur (S) & Iron (Fe) in addition to C, H, O, N.
• Phosphorous is generally absent from the primary structure of proteins.

D-amino acid :

• Amino acids refer to compounds whose molecules contain an amine group (-NH2) and carboxyl group (-COOH).
• All amino acids except for glycine are stereoisomers. This means that there are mirror images of their structure. It is just like how we have left hands and right hands.
• These are labeled L (left-handed) and D (right-handed) to distinguish the mirror images.
• D-Amino acids are occasionally found in nature as residues in proteins.
• Most of the proteins contain L-amino acids.

               

 Additional Information

• Based on the source from which proteins are derived, they are categorized into two main categories –

           i) Animal-based protein           ii) Plant-based proteins

Concept-

Pine moss or wolf moss (Letharia vulpina**) is** a beautiful greenish-brown, bushy moss that grows on the bark of pine and fir trees in the Pacific Mountains of the United States and contains a moderately toxic yellow dye called vulpinic acid.

Key Points

• The thalli or main body is bushy and densely branched, from bright yellow to yellow-green or greenish-yellow, but fades in dry specimens.
• Sizes are typically 2 to 7 cm (0.8 to 3 inches) in diameter.
• There are many Soredia and isidia of vegetative reproductive structure on the surface of the thallus.
• Letharia vulpina is found throughout the Pacific Northwest. Often abundant on bare branches that have lost their bark.
• In old wet forests, they are usually found in dry areas. This species is moderately sensitive to air pollution.
• In the Rocky Mountains, Letharia species is found in the Ponderosa forests on the prairie border at relatively low elevations, but in the Douglas spruce and pine forests at medium to high elevations.

Additional Information

• Also known as true Icelandic moss or Icelandic moss, Cetraria islandica seems to be derived from the name of an upright or upright Icelandic moss whose leaf shape looks like moss.
• Cladonia rangiferina, also known as crustacean moss, deer moss, or grey deer moss, is a species of brightly coloured shrub moss in the family Cladoniaceae. It grows in hot and cold climates in an open environment with good drainage.
• Lecanora esculenta has an approximately round fruit disk (apothecia) bordered by photosynthetic tissue resembling body parts that are not fruiting bodies of lichens (thallus).

Concept-

• Obelia is a genus of hydrozoans, a class of mainly marine and some freshwater animal species that have both polyps and medusae in their life cycle.
• Hydrozoa belongs to the class Cnidaria, which are aquatic (mainly marine) organisms that are relatively simple in structure.
• They are commonly called sea-fur.
• The polyp is the sessile and asexual stage, while medusa is the free-swimming, sexual stage.
• They form small hydroid colonies on rocks or large seaweeds in the form of fur-like growth.

Explanation:

• Coenosarc -
• It is the inner, tubular, living tissue of Obelia colony.
• It encloses a canal called gastrovascular cavity.
• It is surrounded externally by perisarc.
• Perisarc -
• It is the yellow-brown, non-living chitinous layer of Obelia.
• It protects the colony and acts as an exoskeleton.
• It contains annuli that allows some limited movements.
• Medusae are lateral buds that develop as a result of asexual reproduction from the blastostyle.
• Thus medusa is not covered by the perisarc.

Key Points Medusa-

• The medusa may be an adjusted zooid delivered as an empty bud from the coenosarc of the blastostyle in spring and summer. Medusa swims unreservedly on the surface water.
• It is saucer-shaped and joined to the blastostyle by the centre of the raised surface. When completely shaped it breaks free and develops from the mouth of the gonotheca.
• The medusa is circular and modest umbrella-like in shape.
• The arched external surface is known as the ex-umbrella and the concave inward surface is the sub-umbrella.
• From the middle of the sub-umbrella emerges a brief anticipating manubrium, at its pinnacle may be a square mouth encompassed by four verbal projections.
• The mouth leads into an enteric depth or gastric depth within the manubrium.
• From the enteric depth, emerge four outspread canals which are sensitive ciliated tubes, they run to the edge of the chime to connect a ciliated circular canal running close the margin.
• The enteric depression and the canals speak to the enteron which disperses nourishment.
• Anticipating from the centre of the spiral canals are four gonads, since genders are isolated they are either four testicles or four ovaries, they are patches of altered sub-umbrella ectoderm.
• The gonads develop after the medusae elude from the gonotheca.
• The edge of the chime is created inwards as a lean crease called velum.

Additional Information

• The hydranths are nourishing polyps, they nourish by capturing diminutive creatures and hatchlings.
• Towards the base of the hydrocaulus within the axils of the polyps, are regenerative polyps called blastostyles.
• The blastostyles are the regenerative zooids as they replicate asexually to allow rise to various sidelong buds called medusa buds or gonophores.
• These buds create into third sort of zooids of the colony called medusae.
• The polyps, their tubular associations and blastostyles are made of ectoderm, mesogloea and endoderm, these layers are together called coenosarc and its depth is an enteron that is ceaseless and common to all the individuals, through the enteron processed nourishment is disseminated in arrangement.

Concept:

• Enzymes are protein molecules that act as biological catalysts.
• They help in increasing the rate of chemical reactions that take place in living beings.

Explanation:

• All require a coenzyme for their activity: NOT TRUE
• ​Coenzymes are non-protein, organic molecules that can bind to enzymes to enhance or facilitate the enzyme activity.
• They are usually vitamins or vitamin derivatives.
• ​But not all enzymes require coenzymes to function.
• All are active at neutral pH: NOT TRUE
• ​The optimum pH of an enzyme depends on the location where it functions.
• For example, stomach enzymes function in acidic pH, while in small intestine enzymes function in a slightly basic pH.
• Therefore, all enzyme activity do not occur at neutral pH.
• All require a molecule of water for their activity: NOT TRUE
• ​Enzyme activity has been found to be enhanced in the presence of water.
• However, enzymes may still be functional in the absence of water.
• All lower the energy of activation: TRUE
• ​Enzymes increase the rate of reaction by lowering the activation energy.
• Activation energy is the minimum amount of energy required to activate atoms or molecules so that they can undergo chemical transformations in a reaction.
• The lower the activation energy, the faster will be the reaction catalyzed by an enzyme.

The correct answer is 21.

Concept:

• Development of the fertilized zygote into a fully developed foetus or a young one is known as embryogenesis.
• This process can take place in 2 main ways:
• Oviparous - In this type, the development takes place outside the female body. The female lays fertilized eggs and then incubates them to hatch.
• Viviparous - In this type, the development takes place inside the mother's body, such that the mother gives birth to the young ones.
• All birds are oviparous in nature and thus they lay eggs.

Explanation:

• After fertilization, the zygote divides repeatedly and travels down the oviduct.
• As it descends, many protective layers form around it.
• The hard shell in a hen’s egg is one such protective layer.
• The hen finally lays the egg after the hard shell has formed around the developing embryo.
• It takes about 3 weeks (21 days) for the embryo to develop into a chick.
• The mother bird sits on the eggs after they are laid to keep them warm. This process is known as egg incubation.
• The embryos continue to develop within their egg shells.
• After the embryos develop, the eggs hatch.
• The incubation period is different for different birds.

So, the incubation period in chick lasts for 21 days.

The correct option is Bower and Goebel.

Key Points

• (Greek rhiza = root; phora= bearer) It is a leafless, cylindrical structure arising from the stem branching.
• According to Goebel (1905), the organ Rhizophore is neither a root nor a shoot.
• The term "organ sui generis" is Latin phrase that means unique.
• Externally it looks like a root, but occasionally it gives rise to leafy branches.
• So the feature rhizophore in Selaginella (given in figure) has been in controversy whether it is root or a stem.
• They are mostly found in clambering (climb or move in an awkward and laborious way) plant species.
• Bower & Gobel considered it a structure intermediate between the root and stem.

Explanation:

Rhizophore as a Root:

• Studies of various scientist considered that rhizophore is a root because of the following reasons:
• It is positively geotropic.
• It does not bear roots.
• The internal structure of rhizophore is similar to a root.
• The apex of rhizophore shows a root cap-like structure.
• Rhizophore shows auxin transport similar to the root.

Rhizophore as a stem:

• Bruchman, Worsdeles, etc. considered that the rhizophore is more like a stem because of the following facts:
• Root hairs are absent in the rhizophore.
• Rhizophore arises exogenously whereas root arises endogenously.
• It grows by an angle meristem which is an embryonic shoot.
• Under the controlled condition, rhizophore can be induced to grow into a shoot.

Additional Information

• Van Tieghem :
• ​The stele (refer figure) was discovered by two scientists Van Tieghem and Douliot in the year 1886. Stelle actually means ‘pillar’.
• A stele is present in vascular plants. It is the central portion of the root or stem that contains cylinders of vascular (conductive) tissues.
• Harvey Gibson :
• He was a Scottish botanist, phycologist, and academic author.
• His name often appears as R. J. Harvey-Gibson, who designed and oversaw the creation of the Hartley Botanical Institute, Greenfield (U.K.).

Concept-

• Virology started when two bacteriologists, Frederick William Twort in 1915 and Félix d'Hérelle in 1917, freely found the presence of bacteriophages (viruses that infect bacteria).
• Félix d'Hérelle had coined the word 'bacteriophage' which literally means "bacteria eater".

Key Points

• Bacteriophages, commonly known as phages, are viruses that infect and reproduce in bacterial cells.
• They are omnipresent within the environment and are recognized as the foremost inexhaustible organic specialist on soil.
• They are amazingly different in the size, morphology, and genomic organization.
• All comprise of a nucleic acid genome encased in a shell of phage-encoded capsid proteins.
• The nucleic acid can be either DNA or RNA.
• Bacteriophages follow 2 types of life cycles:
• Lytic - These are virulent phages that lead to the lysis (death) of the host cell.
• Lysogenic - These are known as temperate phages as they replicate their genetic material along with that of the host cell without destroying the cell.
• Phages have been extensively used in the laboratory for various research processes.

Additional Information

• Lworf, Horne and Tournier: They proposed a classification system for viruses known as the LHT system.
• D. J. Iwonowski: He was a Russian botanist who was one of the discoverers of viruses.
• Beijerinck: He was a Dutch microbiologist who also contributed towards the discovery of viruses and called them Contagium vivum fluidum.

The correct answer is P. striiformis.

Key Points

Fungi

• The fungi constitute a unique kingdom of heterotrophic organisms.
• Some fungal species are useful (Yeast & Penicillium), some are harmful (Puccinia) which causes disease in plants and some like Candida causes Candidiasis in humans and animals.
• Some are unicellular like Yeast, used in bakery and beer production, while some multicellular fungus causes white spots seen on mustard leaves.
• Most fungi are heterotrophic and absorb soluble organic matter from dead substrates and hence are called saprophytes, some are parasitic.
• They prefer to grow in warm and humid places.
• Reproduction in fungi can take place by vegetative means – fragmentation, fission, and budding.
• When a fungus reproduces sexually, two haploid hyphae of compatible mating types come together and fuse.
• The fungi form fruiting bodies in which reduction division occurs, leading to the formation of spores.
• Fungal spore dispersal takes place via air, therefore it reaches long distances and is allergens in the air.

Explanation:

Yellow Rust (Puccinia striiformis) on Wheat

Puccinia:

• It is a genus that belongs to the Kingdom Fungi.
• It includes species that cause serious infections on crop plants called rust.
• These fungi cause rusty pustules (bulging patches) on the aerial parts of crops.

Yellow Rust disease

• It also affects - wheat, barley, rye stems, leaves, and grains also.
• It appears as yellow stripes of powder or dust on leaves and leaf sheaths of the Wheat crop.
• This yellow powder comes out on clothing or fingers when touched.
• The disease can spread rapidly under congenial conditions and affects crop development, and eventually the yield.
• Yellow rust is a devastating seasonal disease in India.

Additional Information

Explanation:

• Phosphoenolpyruvic acid or PEP is a compound that serves as primary acceptor in the mesophyll cell cytoplasm of plants like maize, sugarcane, Sorghum etc.
• These plants are known as C4 plants that are specially adapted for CO₂ fixation at its lower concentrations, like when the stomata are closed to reduce transpiration.

Key Points

• In the C4 plants, two pathways run for CO₂ fixation - C3 Cycle or Calvin cycle & C4 Cycle or Hatch and Slack Pathway.
• The primary CO₂ acceptor is 3-carbon molecule phosphoenolpyruvate (PEP) and is present in the mesophyll cells.
• The enzyme responsible for this fixation is PEP carboxylase or PEPcase.
• It is important to register that the mesophyll cells lack the RuBisCO enzyme.
• The C4 acid Oxaloacetate (OAA) is formed in the mesophyll cells.
• It then forms other 4-carbon compounds like malic acid or aspartic acid in the mesophyll cells themselves, which are transported to the bundle sheath cells.
• In the bundle sheath cells, these C4 acids are broken down to release CO₂ and a 3-carbon molecule.
• The 3-carbon molecule is transported back to the mesophyll where it is converted to PEP again, thus, completing the cycle.
• The CO₂ released in the bundle sheath cells enters the C3 or the Calvin pathway, a pathway common to all plants.
• The bundle sheath cells are rich in the enzyme Ribulose bisphosphate carboxylase-oxygenase (RuBisCO), but lack PEPcase.
• Thus, the basic pathway that results in the formation of the sugars, the Calvin pathway, is common to the C3 and C4 plants.

Concept:

• Inspiration: It is the process of breathing air into the lungs.
• Expiration: It is the process of breathing air out of the lungs.

Key Points

• Tidal volume (TV): It is the amount of air delivered in and out of the lungs with each breath. It measures around 500ml.
• Residual volume (RV): It is the amount of air left in the lungs after maximum exhaling. It measures 1200ml.
• Vital capacity: It is the total amount of air that can be expired after a maximum inspiration.
• Inspiratory reserve volume (IRV):  It is the extra forceful inspiration after a normal inhalation. It measures 3000 ml.

Additional Information

• Expiratory reserve volume (ERV): It is the extra forceful expiration after a normal exhalation. It measures 1100ml.
• Inspiratory capacity: The maximum amount of inspiration after maximum expiration.
• Functional residual capacity: The volume remaining in the lungs after a normal, passive exhalation.
• Total lung capacity: It is the total amount of air lungs can hold.

The correct answer is Abundance of carbon dioxide.

Concept:

• Hydra belongs to Coelenterata (Cnidaria Phylum).
• Hydra are fresh living water organisms.
• Hydra occurs in cool, clean freshwater of ponds, lakes and streams
• It reproduces by both asexual and sexual modes.

Explanation:

• Gonads are ecotodermal in Hydra.
• During the autumn months, sexual reproduction in Hydra begins with the development of temporary structures known as gonads.
• Actually, sexual reproduction occurs under unfavorable conditions such as excessively high and low temperatures in the water in which hydra lives.
• An increase in the amount of free carbon dioxide in the surrounding water can also lead to the formation of gonads in Hydra.

Thus, the formation of gonads in Hydra is stimulated by the abundance of carbon dioxide.

The correct answer is Funaria.

Concept:

• Mosses and liverworts are plants that belong to the phylum Bryophyta.
• They are amphibious plants that can live on land but are dependent on water for sexual reproduction.
• They are found commonly growing in moist shaded areas in the hills.
• It is thallus-like, prostrate or erect, and attached to the substratum by unicellular or multicellular rhizoids.
• They may possess root-like, leaf-like or stem-like structures.
• The main plant body of the bryophyte is haploid and produces gametes, hence is called a gametophyte.
• The sex organs in bryophytes are multicellular.
• The male sex organ is called antheridium and they produce biflagellate antherozoids.
• The female sex organ, called archegonium, is flask-shaped and produces a single egg.
• Zygotes do not undergo reduction division immediately, but produce a multicellular body called sporophyte.
• The sporophyte is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it.

Important Points

• The gametophytic plant body bears rhizoids, stem-like and leaf-like structures.
• The gametophore is erect and slender, attaining a height of 1-3cm or more.
• The rhizoids arise from the base of the stem in form of tufts.
• Each rhizoid is multicellular, filamentous, branched and contains oblique septa.
• They are colourless when young, but become brownish at maturity.
• Some exposed rhizoids may develop chlorophyll and called as chloronemal branch.
• Their primary function is absorption and anchorage.

Additional Information

Type of Rhizoid in Riccia

• Riccia however, rhizoids are unicellular and unbranched structures.
• They anchor the thallus of the plant to the substrate and usually are of two types - smooth-walled and tuberculated.
• These rhizoids are present in the mid-rib region of the thallus.

Type of Rhizoids in Marchantia

• Marchantia polymorpha has two types of rhizoids - tuberculate rhizoids and smooth-walled rhizoids.
• Multicellular purple-colored scales with single-cell thickness and unicellular rhizoids are present on the ventral surface of the thallus.

Concept-

• Alginic acid, also called algin, is an edible polysaccharide found in brown algae.
• It is a hydrophilic biopolymer formed by chains of polyuronic acids.
• It is obtained from brown algae such as Laminaria.
• With metals such as sodium and calcium, its salts are known as alginates.

Key Points

• Alginic acid is a linear polymer of β-1,4-linked D-mannuronic acid and a C-5 epimer, L-guluronic acid.
• Alginic acid forms the major cell wall constituent of brown algae.
• It is present in the form of mixed salts of Na⁺, Mg²⁺ and Ca²⁺ ions.
• Commercial sources of alginic acid include species of Laminaria, Macrocystis and Ascophyllum.
• It is widely used in industry for various gelling purposes.
• It is an approved food ingredient to be used as an emulsifier, stabilizer and thickener in food.
• It is also used in the pharmaceutical industry for making tablets.

The correct answer is Ascomycetes.

Explanation:

• Lichens are symbiotic associations between algae and fungi.
• The most common mycobionts in lichen belong to Ascomycetes.
• The fungal component is called mycobiont and the algal component is called photobiont.
• The photobiont is the photosynthetic part of a lichen.
• The fungal component or mycobiont is involved in:

1. Outer covering for protection.
2. Attachment to substratum
3. Protection against harmful radiations.

• Lichens are found in habitats like walls, window panes, barren rocks, cooled volcanic larva, tree bark, soil and aquatic habitats.
• Mycobionts provide algae with shelter while also absorbing minerals and water.
• Lichens are often referred to as pollution indicators.
• Lichens are named as the mycobiont as they are the more prominent component.
• On the basis of the mycobiont, lichens are divided into:
• Ascolichen - They are formed by Ascomycetes fungi.
• Basidiolichen - They are formed by Basidiomycetes fungi.

Ascomycetes- 

• The members of Ascomycetes are commonly called as sac fungi.
• They are mostly multicellular (Penicillium) and rarely unicellular (yeast).
• A number of Ascomycetes are parasites on plants, animals and humans.
• In most of the lichens, the fungal component belongs to Ascomycetes.
• Examples of Ascolichen:
• Cetraria (Iceland moss)
• Cladonia rangifera (Reindeer moss)

Concept-

• Cellular movement is accomplished by cilia and flagella.
• Flagella are whip-like appendages that undulate to move cells.
• They are longer than cilia, but have similar internal structures made of microtubules.
• Prokaryotic and eukaryotic flagella differ greatly.
• Cilia are hair-like structures that can beat in synchrony causing the movement of unicellular Paramecium.
• Cilia are also found in specialized linings in eukaryotes.
• For example, cilia sweep fluids past stationary cells in the lining of trachea and tubes of female oviduct.

Key Point

• Both cilia and flagella are covered with the cell membrane.
• Their core, called the axoneme, has a number of microtubules running parallel to the axis.
• Both flagella and cilia have a 9 + 2 arrangement of microtubules.
• The axoneme consists of 9 doublets of peripheral microtubules that are arranged radially surrounding a central pair of microtubules.
• This type of arrangement of axonemal microtubules is called 9 + 2 arrays (doublet + 2 singlets).
• Each of the microtubule doublets consist of a complete microtubule paired with a partially completed microtubule.
• The complete microtubule has 13 subunits or protofilaments and is called A tubule.
• The partially completed microtubule has 10-11 protofilaments and is called B tubule.
• There are radial spokes that radiate from the A tubule inwards towards the central microtubule pair.
• The dynein proteins project out from the sides of the A tubule in the form of 2 arms - outer and inner.
• Dynein "arms" attached to the microtubules serve as the molecular motors.
• These are motor proteins that create mechanical energy from chemical energy acquired from ATP hydrolysis enabling movement along microtubules.

Additional Information

• Defective dynein arms cause male infertility as sperm tail is a flagellar structure.
• It may also lead to respiratory tract and sinus problems as cilia covers these tracts.

The correct answer is Rennin.

Key Points

• Enzymes are substances (proteins) that act as a catalyst to speed up the metabolism or chemical reactions that occur in our body.
• This results into break down of complex molecules into simpler ones.
• Enzymes help to digest your food.
• This allows the nutrients in food to be easily absorbed into the bloodstream and carried throughout the body.
• They are secreted by salivary glands, pancreas, cells lining the stomach, and small intestine.

Explanation:

Rennin

• Renin is also known as Chymosin.
• It is a type of digestive enzyme secreted by the chief cells in the stomach to digest milk protein.
• Rennin is present in infants as their major diet contains a large amount of milk
• However, adults do not consume a huge amount of milk and hence they lack Rennin enzyme.

Additional Information

The correct answer is Uredospore.

Concept:

• Puccinia graminis is a fungi which uses wheat plants as primary host.
• The dikaryotic phase is completed in the wheat plant.
• The dikaryotic mycelium is well-developed, branched and has two main spore stages - Uredinal and telial.
• The uredinal stage is when the uredospores are formed.
• The Uredospores of Puccinia graminis is formed on wheat.

Explanation:

• Primary infection in wheat begins with the aeciospore germination.
• When the aeciospore reaches the wheat plant, it may attack the leaf, stem, or glumes.
• The dikaryotic mycelium then forms a mass of hyphae below which uredia are formed sub-epidermally.
• The uredia give rise to vertical hyphae in a palisade-like layer.
• The uredia bear uredospores at their swollen tips and form groups called uredosorus.
• Thus, uredospores form in groups known as uredosorus under the epidermis, and appear as reddish-brown pustules.
• The developing uredosori exert pressure on the epidermis such that the pustules rupture.

Important Points

• Uredospores are oval, stalked, unicellular, and binucleate.
• They are thick-walled spores, with 4 round equatorial germ pores.
• The uredospore wall can be differentiated into 3 layers:
• Pellicle - outer layer.
• Exosporium - middle layer.
• Endosporium - inner layer.
• The uredospores can be dispersed by the wind and hence spread rust to other plants.
• In favourable conditions (i.e., during the winter season), the uredospores germinate to infect the wheat plant.
• During a single season, the procedure may be repeated several times.

The correct answer is two.

Hint

Genus (Singular) or Genera (plural) 

• A genus is a taxonomic rank among the eight major taxonomic ranks in biological classification. It is below the family and above the species.

Key Points

• Chordates & their characteristics 
• Presence of Notochord.
• The central nervous system is dorsal, hollow, and single.
• Pharynx perforated by gill slits.
• The heart is central.
• A post-anal part (tail) is present.
• Phylum Chordata is divided into three subphyla- Urochordata, Cephalochordata and Vertebrata.

Explanation:

• Cephalochordata, often referred to as protochordate, is a taxon of marine invertebrate chordates comprising 30 species belonging to two genera -

1. Branchiostoma (earlier known as Amphioxus)
2. Epigonichthys (earlier called Asymmetron).

• Taxonomic Classification:
• Kingdom - Animalia
• Super-phylum - Deuterostomia
• Phylum - Chordata
• Sub-phylum - Cephalochordata
• Class - Leptocardii
• Family - Branchiostomatidae
• Genus - (1) Branchiostoma and (2) Epigonichthys (or Asymmetron)

Additional Information

Characteristics of Amphioxus (also known as Lancelet)

• Cephalochordata is additionally called acrania.
• They belong to any of the two dozen species having a place with the subphylum Cephalochordata of the phylum Chordata.
• Habit: They are exclusively marine, small fish-like animals that rarely exceed 5 cm in length.
• Habitat: Lancelets partly live buried in soft marine sediments.
• Notochord: It extends throughout the length of the body and is present throughout life.
• Tail: Post-anal tail is present.
• Circulatory system: Closed circulatory system is present.
• Body fluid: Blood is without pigment.

The correct answer is heredity.

Hint

Heredity:

• It is the transmission of genetic characteristics (traits) from parents to offspring.
• As a result, the offspring look similar in some aspects to parents.
• Heredity takes place through reproduction.
• Traits may be - color, height, skin complexion, etc.

Reproduction: 

• It is the process by which (parent) organisms give rise to new young ones (offspring).
• Reproduction is either asexual or asexual.
• In asexually reproducing organisms offspring looks identical to parents like plants and bacteria
• However, in sexually reproducing organisms variation (differences in traits) arise in offspring.

Inheritance:

• Process of transfer of genetic traits and their expression from one to another generation.
• Genetic information is stored in the DNA, which can be passed on to the next generation through reproduction..

Explanation

 

Mistake Points

• Please note that 'heredity' and 'hereditary' are words with different meanings.
• 'Heredity' refers to the process of transfer of characters from one generation to another.
• Whereas, 'hereditary' refers to the character that can be transferred from one generation to another.
• For example, haemophilia is a hereditary disease, meaning it can be transmitted by heredity.

The correct answer is 33.

Key Points

• Hirudinaria granulosa is a scientific name of Common Indian Cattle leech.
• It is a blood-sucking (sanguivorous) ectoparasite on cattle and humans.
• It is found in freshwater tanks, ponds, lakes, swamps, and slow streams.
• It takes food by sucking the blood of fishes and frogs, and also of cattle or human beings when they enter the pond.
• Taxonomic classification of H. granulosa 
• Kingdom - Animalia
• Phylum - Annelida
• Class - Clitellata
• Sub-class - Hirudinea
• Order - Gnathobdellida
• Family - Hirudinidae
• Genus - Hirudinaria
• Species - H. granulosa

Explanation

• The body of Hirudinaria is soft, vermiform, elongated, bilaterally symmetrical, and metamerically segmented.
• There are 33 body segments, each having five superficially marked annuli except the few anterior and posterior ones.
• The segments can be divided into 6 regions:​​

 

Additional InformationGeneral characteristics of Hirudinaria :

• The body is elongated with the convex dorsal surface and flat ventral surface.
• The dorsal surface is dark green, and the ventral surface is yellowish-brown.
• Size varies from 6 to 10 cm in length.
• However, leeches may contract or elongate their body much beyond the limits mentioned.
• The body surface always remains moist due to the secretion of mucus from the body wall.
• At the anterior end on the ventral surface, a cup-shaped anterior sucker is present.
• The mouth is present in the center of the anterior sucker.
• A ventral sucker is also present at the posterior end of the body.
• Anus is present on the dorsal side at the junction of the last metamere and the posterior sucker.
• Hundred or more very closely arranged grooves or annuli are present on the body surface.
• Each of the five anterior metameres bears a pair of eyes on the dorsal margin, each looking like a dark spot.
• There are 17 pairs of ventro-laterally arranged nephridiopores in the metameres starting from 6th to 22nd metameres.
• The male and female genital apertures are present on the ventral side in the middle of the 10th and 11th metameres.

Mistake Points

• Please note that the official answer key shows option 1 as the correct answer but we have marked option 4.
• Also note that the options given for this question are a little ambiguous and so, we are choosing the best possible answer.
• Option 1 is a characteristic feature of Amphioxus and hence, it cannot be "not true".

Key Points

• Notochord persists throughout life: TRUE
• Amphioxus belongs to the sub-phylum Cephalochordata of Chordata phylum.
• ​The notochord in Amphioxus extends the whole length of the body.
• It is persistent throughout its life, which is a distinctive feature of Cephalochordata.
• ​Nerve cord dorsal to notochord: TRUE
• The central nervous system of an adult Amphioxus consists of a tubular nerve cord.
• The nerve cord lies dorsally to the notochord.
• Brain absent; very little cephalization: TRUE
• Cephalization is the process in which the nervous and sensory tissues become organized in the head region that marks the anterior end of the animal.
• Amphioxus does not have enough cephalization to form a head or brain.
• It has a swelling of the nerve cord at the anterior end that forms a brain vesicle.
• The very little cephalization involves the feeding structures being organized towards the anterior end along with a pigment spot.
• Free swimming organism: NOT TRUE
• Amphioxus larvae are free-swimming but adults usually do not swim.
• Adults are burrowing animals that live in shallow waters and remain buried in the sand for most part.

Key Points

• Scoliodon or dogfish is a cartilaginous fish belonging to the class Chondrichthyes.
• There are 10 pairs of cranial nerves arising from different parts of the brain and are distributed in the anterior region of the body.

 

Concept:

• Phyllotaxy is the pattern of arrangement of leaves on the stem or the branch of a plant.
• There are 3 main types of phyllotaxy:
• Alternate - A single leaf arises from each node. E.g. - China rose, Mustard.
• Opposite - A pair of leaves arise at each node and lie opposite each other. E.g. - Guava, Calotropis.
• Whorled - More than 2 leaves arise at each node and form a whorl. E.g. - Alstonia, Nerium.

Additional Information

• There are some other spiral forms of phyllotaxy in which leaves are arranged in vertical rows called orthostichies.
• These are of the following types:
• Distichous - There are 2 orthostichies so that every 3rd leaf base is vertically above the 1st leaf base. E.g. - Graminae.
• Tristichous - There are 3 orthostichies such that every 4th leaf base is vertically above the 1st leaf base. E.g. Cyperaceae.
• Pentastichous - There are 5 orthostichies so that every 6th leaf base is vertically above the 1st leaf base. E.g. - Ficus benghalensis.
• Octastichous - There are 8 orthostichies so that every 9th leaf base is vertically above the 1st leaf base. E.g. - Carica papaya.

Concept-

• Essential fatty acids are those fatty acids which we get from the food supplement and that the body cannot produce.
• It is used to fulfill the requirement of fatty acids for biological processes.

Key Points

• Linoleic acid (LA) is an omega-6 fatty acid which is considered an essential fatty acid because it cannot be synthesized by humans.
• In all omega-6 (ω6 or n-6) fatty acids, the first double bond is located between the sixth and seventh carbon atom from the methyl end of the fatty acid.
• Linoleic acid is a colorless to straw colored liquid.
• It is a polyunsaturated fatty acid essential to human diet.
• After consumption and absorption by enterocytes lining the small intestines, linoleic acid is packaged into chylomicrons as phospholipids, triacylglycerols, or cholesterol esters and enters the general circulation (subclavian vein) via the thoracic duct.
• Linoleic acid is delivered to hepatic and extrahepatic tissues as chylomicrons are delipidated en route to and cleared by the liver during its transition to much smaller remnant particles.
• After cellular uptake, the fate of linoleic acid is determined by the needs of the tissue, i.e., incorporation into membrane phospholipids, desaturation and elongation, etc.
• The major dietary sources of linoleic acid are vegetable oils, nuts, seeds, meats, and eggs.

Additional Information Acetic acid-

• Acetic acid is an aliphatic organic acid.
• It is a hygroscopic, corrosive liquid with a vinegar-like odor.
• It can be synthesized by oxidizing acetaldehyde in the presence of manganese or cobalt salts.
• It is utilized for synthesizing acetic anhydride, cellulose acetate and acetic esters.

Propionic acid-

• Propionic acid is a short-chain saturated fatty acid comprising ethane attached to the carbon of a carboxy group.
• It has a role as an antifungal drug. It is a short-chain fatty acid and a saturated fatty acid. It is a conjugate acid of a propionate.
• Propionic acid (PA) is used as a preservative in foods such as cheeses, baked goods, or additive for artificial fruit flavors.

Palmitic acid-

• Palmitic Acid is a saturated long-chain fatty acid with a 16-carbon backbone.
• Palmitic acid is found naturally in palm oil and palm kernel oil, as well as in butter, cheese, milk and meat.
• It is a long-chain fatty acid and a straight-chain saturated fatty acid. It is a conjugate acid of a hexadecanoate.

The correct answer is Plasmin.

Concept:

• Fibrinolysis is the process by which blood clots are prevented from growing and becoming problematic.
• Primary fibrinolysis is a body process, whereas secondary fibrinolysis is the breakdown of clots caused by a medication, a medical issue, or another factor.
• Fibrinolysis is the breakdown of a fibrin clot, which is the result of coagulation.

​Explanation:

• In the liver, plasminogen, an inactive form of plasmin, is produced.
• Despite the fact that plasminogen cannot cleave fibrin, it has an affinity for it and is incorporated into the clot when it forms.
• Plasmin degrades fibrin into soluble components known as fibrin degradation products (FDPs).
• FDPs compete with thrombin, which is the enzyme to convert fibrinogen to fibrin.
• Hence they slow down the formation of blood clots by blocking fibrinogen conversion to fibrin.
• These fibrin monomers otherwise polymerize to form long, sticky fibres.
• The fibrin threads form a fine network of threads, in which dead and damaged formed elements of blood are trapped.
• Plasmin is the proteolytic enzyme that inactivates the coagulation factors by cleavage.
• Thus, plasmin is fibrinolytic as well as anticoagulant in function.
• It plays a crucial role in removing unnecessary clots in blood vessels and restoring normal blood flow.

 Additional Information

• Hemin-
• ​It is made from red blood cells extracted from human blood.
• Hemin acts by lowering the production of a specific enzyme in the body.
• Thrombin-
• ​It acts as a proteolytic enzyme to convert fibrinogen molecule to insoluble fibrin monomer.
• It is obtained by the activation of prothrombin.
• Prothrombin-
• ​It is called Factor II and is the inactivated form of thrombin.
• It is synthesized in the liver in the presence of vitamin K.