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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.