Search Previous Year Questions

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.