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Key Points

• Prokaryotes are microscopic single-celled organisms belonging to the domains Bacteria and Archaea.
• Structurally, the cells have cell wall and may also be encased in a capsule or slime layer.
• They lack any membrane-bound organelle and hence do not even have nucleus.
• They usually have circular chromosomal DNA and may also have an extra-chromosomal DNA called plasmid.
• Some of the prokaryotes may have flagella but are distinct from that of the eukaryotes.

Additional Information

The correct answer is Solenostele.

Explanation:

• The stele is the central part of a vascular plant's root or stem that contains tissues developed from the procambium.
• These include vascular tissue, ground tissue (pith), and a pericycle, which, if present, defines the stele's outermost boundary.
• The endodermis, the cortex's innermost cell layer, is located outside the stele.
• Siphonostele is a protostele or medullated protostele with a central non­-vascular pith that is devoid of leaf gaps.
• Siphonostele is classified into two types:
• Amphiphloic siphonostele - which has a central pith and xylem that is surrounded on both sides by phloem, pericycle, and endodermis. E.g.- Marsilea.
• Ectophloic siphonostele - the central pith is surrounded by pericycle, xylem, phloem, and endodermis.
• Solenostele - It is similar to siphonostele but the vascular cylinder is dissected at places by leaf gaps, from where leaf traces originate.
• Thus they have non-overlapping leaf gaps.
• Today, this type of stele is mostly found in fern stems.
• Solenostele can also be of 2 types - amphiphloic or ectophloic depending on the siphonostele from which they develop.

Additional Information Dictyostele

• If there are multiple gaps in the vascular cylinder in any one transverse section, this is referred to as dictyostele.
• The numerous leaf gaps and leaf traces give the appearance of many isolated xylem islands surrounded by phloem on a dictyostele.
• A meristele is any of the isolated units of a dictyostele. This type of stele is only found in the stems of ferns among living plants.

Eustele

• In this, the primary vascular tissue is made up of vascular bundles that form one or two rings around the pith. In addition to stems, the eustele can be found in the roots of monocot flowering plants.
• A eustele's vascular bundles can be either collateral (with the phloem on only one side of the xylem) or bicollateral (with phloem on both sides of the xylem, as in some Solanaceae).

Key Points

• A frog belongs to the class Amphibia.
• They have a characteristic 3-chambered heart with 2 auricles and 1 ventricle.
• They have a closed circulatory system and incomplete double circulation.
• Sinus venosus is the pacemaker in the heart.

Additional Information

• 2-chambered heart is present in fishes.
• 3-chambered heart is present in amphibians and reptiles. Exception - Crocodiles have 4-chambered heart.
• 4-chambered heart is present in birds and mammals.

Key Points

• Conidia are a type of asexual reproductive spore produced by fungi.
• Conidiophores are specialized branches of hyphae that bear the conidia on their tips.
• They arise at right angles to the hyphae.
• Penicillium species are often recognized by the branching patterns of the conidiophores.
• They can be simple or branched and are terminated by clusters of phialides.
• The spores are formed in chains with the youngest one towards the base.

Additional Information

• Rhizopus - It produces sporangiospores and not conidia.
• Ustilago - It produces basidiospores and teliospores.
• Saccharomyces - It mostly reproduces by budding.

Key Points

 Gregor Mendel gave the Laws of Inheritance based on his experiments on Pisum sativum (garden pea):

• Law of Dominance -
• It states that characters are controlled by discrete units called factors (alleles) which occur in pairs.
• It also states that in a dissimilar pair of alleles, one of the alleles is expressed (dominant) over the other (recessive).
• Law of Segregation - 
• It states that alleles do not show any blending and both parental characters are recovered in the F2 generation.
• It also states that during gamete formation, alleles of a pair separate in such a way that one gamete receives only one of the two alleles of a pair.
• It is also known as the Law of purity of gametes.
• It can be proved with a monohybrid cross.
• Law of Independent Assortment -
• It states that when 2 pairs of traits are combined in a hybrid, segregation of one pair is independent of the other pair.
• It can be proved with a dihybrid cross.

Additional Information

• Law of Natural Selection -
• It was given by Charles Darwin.
• It states that individuals with more favourable characters survive better and leave more progeny that again survives better and are hence selected by nature.

Concept:

• Nitrogen is required by plants for various processes, yet they cannot utilize the nitrogen present in the air.
• Nitrogen fixation is the process by which the atmospheric nitrogen is converted to ammonia-like, nitrates and nitrites which can be absorbed by plant roots.
• It is carried out by specific microbes which can be:
• Free-living like cyanobacteria
• Symbiotic like Rhizobium associated with leguminous plants.
• Ammonia is formed from atmospheric nitrogen with the help of the enzyme nitrogenase.

Key Points

• Cyanophyta is often referred to as blue-green algae.
• It was later recategorized as Cyanobacteria, a type of gram-negative bacteria.
• It differs from other algae as it has a prokaryotic cell structure.
• Its ability to bind atmospheric nitrogen enables it to survive in nutrient-poor habitats.
• They are also used as biofertilizers as they increase soil fertility by enriching the soil with nitrogen.

Concept:

• Axile placentation - Ovules are attached to axial placenta in a multilocular way. E.g. - Tomato (Solanaceae)
• Epipetalous - It is the condition where stamens are united with petals. E.g. - Brinjal (Solanaceae)
• Solanaceae also has an unique feature of an oblique septum in the ovary.

Mistake Points

• Liliaceae does have axile placentation but are not epipetalous.
• Graminae have basal placentation.
• Malvaceae have both axile placentation as well as epipetalous androecium, but do not have oblique ovary.

Additional InformationThe reproductive features of Solanaceae family are:

• Inflorescence - Solitary, axillary or cymose
• Flower - Bisexual and actinomorphic
• Calyx - 5 Sepals, united, persistent and valvate
• Corolla - 5 petals, united and valvate
• Androecium - 5 stamens and epipetalous
• Gynoecium - Bicarpellary, syncarpous with superior bilocular ovary that is obliquely placed and axile placentation.
• Fruit - Berry or capsule.
• Seed - Endospermous

Concept-

• Aurelia is a common jelly-fish or moon-jelly, occurs in coastal waters of tropical and temperate oceans of the world close to the surface of water.
• It is cosmopolitan in distribution.
• It belongs to class Scyphozoa (phylum Cnidaria).

Key Points

• The medusa of Aurelia is flattened, bowl or saucer-shaped gelatinous structure called the bell or umbrella.
• It exhibits tetramerous radial symmetry. It usually measures about 7.5-10 cm in diameter, though much larger forms measure up to 30 cm in diameter.
• The bell or umbrella is distinctly divided into a slightly convex upper surface and a concave lower surface.
• The convex surface is known as exumbrellar surface and the concave surface is known as subumbrellar surface.
• The margin of umbrella is circular which is broken by eight notches.
• Each notch is provided with a pair of marginal lappets enclosing sense organ called tentaculocyst or rhopalium.
• The margin of umbrella, in between notches, is provided with numerous, small, closely arranged hollow marginal tentacles.
• The margin of umbrella, bearing marginal lappets and marginal tentacles, is thin ridge-like called velarium or pseudo velum.
• A true velum like those of hydrozoan medusae is absent in Aurelia because it lacks muscles and nerve ring.

Additional Information Nematocyst-

• Nematocysts or cnidocysts represent the common feature of all cnidarians.
• They are large organelles produced from the Golgi apparatus as a secretory product within a specialized cell, the nematocyte or cnidocyte. Nematocysts are predominantly used for prey capture and defense, but also for locomotion.

Lappets-

• The edge of the bell is often divided into rounded lobes known as lappets, which allow the bell to flex. In the gaps or niches between the lappets are dangling rudimentary sense organs known as rhopalia, and the margin of the bell often bears tentacles.

Key Points

• Virion is the complete infectious virus particle that can exist outside the host cell.
• It consists of:
• Capsid - It is the outer protein layer made up of smaller subunits called capsomeres.
• Core - It is the inner part containing the nucleic acid (DNA or RNA).
• Hence, the virion is also known as 'nucleocapsid'.
• The main function of the capsid is to protect the viral genome.
• It also helps in attaching the virion to specific receptors on host cell during infection.

Mistake Points A virus is different from a virion because unlike virions, they cannot survive outside the host cell.

Additional Information

• For infecting a cell, the virion attaches to the the cell surface by means of receptors.
• The nucleic acid is then injected into the host cell for viral replication.
• The increased number of virions help in infecting more cells.

Key Points

• Voice is produced due to the vibration of the vocal cords.
• Vocal cords are a pair of tissue that stretches at the top of the trachea.
• Vocal cords are enclosed in the thyroid cartilage.
• The cords, muscles and cartilages together form the larynx or the voice-box.

Explanation:

• When we try to produce sound or speech, the lungs blow air against the cords in a nearly-closed position.
• As air tries to push through the small space, it makes the cords vibrate.

Mistake Points As the air that makes them vibrate comes from the lungs, it has to be the expired air and not the inspired air.

Additional Information

• Ligaments - are bands of connective tissue that help to connect bones and joints.
• Tendons - are fibrous connective tissue that connects muscles to bones.