31 Year NEET Previous Year Questions: Biological Classification - 3 - NEET MCQ

Rhizobium is a symbotic nitrogen fixing bacteria. Streptomyces is source for streptomycin. Spirulina is a rich source of vitamin B₁ and proteins.

Retroviruses have RNA as the genetic material and hence they exhibit reverse transcription whereby DNA is synthesized on RNA template. They have reverse transcriptase  as the enzyme.

This phenomenon has been successfully used in genetic engineering to produce disease resistant varieties of plants.

Viruses like bacteriophage T4 undergo lytic cycle that involves lysis of bacteria. The replication cycle of bacteriophage T4 consists of following phases
(i) Adsorption of the phage to bacterial or host cell. Then the viral genetic material penetrates into the host cell.
(ii) Eclipse period involves the synthesis of new phage DNA and proteins.
(iii) Maturation involves the assembly of phage DNA into the protein coat.
(iv) Lysis of host cell occurs and releases infective progeny phases.

Binary fission in diatoms reduces the size of most daughters which is corrected through the development of auxospores.
In some filamentous cyanobacterial forms unisexual reproduction occurs by hormogonia (hormocysts). They are identified by presence of biconcave (one disk or separation disc between two adjacent cells e.g. Oscillatoria).

Frankia, aerobic Gram-positive actinomycetes can induce root nodules in about 8 families. These bacteria cannot fix nitrogen in free living state. They can infect the host root by intracellularly by infecting curled root hair or intercellularly by penetrating between two rhizoderm cells and then progress toward cortical cells. These bacteria in free-living state form diazovesicles containing nitrogenase which is protected from oxygen by a series of laminated lipid layers.

So all the statements are correct.

Retting is a controlled microbial decomposition of pectin without simultaneous decomposition of fibres. Retting process is used for obtaining fibres from steins of flax, hemp, jute etc. For this purpose stems of fibre yielding plants are immersed in water for Song period where decomposition sets in. Retting is facilitated by anaerobic butyric acid bacteria such as Clostridium botulinwn, Clostridium tetani and Clostridium perfringens. These bacteria primarily decompose the plant pectin thus freeing the fibres. If process of retting continues for a long time then cellulose fermenting bacteria develop and destroy the fibres.

Lichens (coined by Theophrastus) are composite or dual organisms which are formed by a fungus partner or mycobiont (mostly ascomycetes) and an algal partner (mostly blue green algae). Fungus forms the body of lichen as well as its attaching and absorbing structures. Algae performs photosynthesis and provides food to the fungus

Neomycin is the antibiotic which inhibit the translation of bacterial cell so that it can not affect the host cell.

Cilia are fine hair-like vibratile, cytoplasmic processes borne by certain cell types. Their movement either propel the organism or move the medium past a fixed cell. The cilia are enclosed by a unit membrane which is an extension of the plasma membrane of the cell. Within the membrane, is a fluid matrix having a supporting axial shaft, or axoneme. The axoneme is composed of eleven microtubules. Two microtubules are single and lie at the centre with a gap in-between. They are called central singlets. The remaining nine microtubules are double and lie in a ring around the central microtubules. The two microtubules forming a doublet are named A and B subtubules. The microtubules, single as well as double, are composed of the globular units of the protein tubulin. The arms of A microtubules contain protein dynein. The latter is ATPase enzyme which catalyzes the hydrolysis of ATP to ADP and transfers the free energy released directly to ciliary work.

So, the correct answer is 'The organized beating of cilia is controlled by fluxes of Ca²⁺ across the membrane'.

The thalloid body of slime moulds is made up of multinucleated cell which lacks septa in between and hence it is a multinucleated single celled mass called plasmodium.

Mucor is a fungus and most of the fungi require the optimum temperature of about 15-30ºC, good moisture content in atmosphere and not very dark and not very lightened place. So the Mucor requires a temperature of about 25ºC, humidity about 95% and a shady place to grow fully.

Mad cow disease is actually Bovine Spongiform Encephalopathy or BSE. In this disease cattles in Britain got their brain become spongy & ultimately gradual degradation of nervous system. It is caused by some virus like but nucleic acid devoid proteinaceous particles called prions (proteinaceous infectious particle).

While working at the Rockefeller Institute, Brown reported isolation of a PPLO from human arthritic joint tissue in 1938. In 1949, Diennes reported to the 7th International Rheumatology Congress the isolation of PPLO from the genitourinary tracts of men afflicted with arthritis. In discussing the significance of this observation, Brown reported successful treatment of arthritic patients in 1949 with a new antibiotic called aureomycin (Clark, 1997).

The class Basidiomycetes includes those members that produce their basidia and basidiospores on or in a basidiocarp.

Ergot of Rye is a plant disease that is caused by the fungus Claviceps purpurea. The so-called ergot that replaces the grain of the rye is a dark, purplish sclerotium, from which the sexual stage, of the life cycle will form after over wintering.

Physarum polycephalum belongs to phylum Amoebozoa, infraphylum Mycetozoa, and class Myxogastrea. P. polycephalum, often referred to as the “many-headed slime,” is a slime mold that inhabits shady, cool, moist areas, such as decaying leaves and logs.

Downy mildew of grapes disesase is linked to the discovery of Bordeux mixture as a popular fungicide. Bordeux mixture was discovered by Millardet in France in 1882. Bordeux mixture is prepared by dissolving 40g. of copper sulphate and 40 g of calcium hydroxide in 5 litres of water. Bordeux mixture is used primarily as a fungicide, it was first used to control downy mildew disease of grape-vine caused by a fungus, Plasmopara viticola. The first pesticide to be used commercially was bordeux mixture.

Bacterial leaf blight of rice is caused by a species of Xanthomonas. Mature rice plant infected by these bacteria, lesion begins as water soaked stripes on the leaf blades and eventually would increase in length and width becoming yellow to grayish-white until the entire leaf dries up. 

A domain of prokaryotic organisms containing the archaebacteria including the methanogens, which produce methane; the thermoacidophilic bacteria, which live in extremely hot and acidic environments, & the halophilic bacteria, which can only function at high salt concentrations are abundant in the world’s oceans. 

Thermococcus, Methanococcus and Methano bacterium exemplify archaebacteria that contain protein homologous to eukaryotic core histones.

Late blight is caused by the fungus Phy-tophthora infestans. Late blight appears on potato or tomato leaves as pale green, water-soaked spots, often beginning at leaftips or edges. The circular or irregular leaf lesions are often surrounded by a pale yellowishgreen border that merges with healthy tissue. Lesions enlarge rapidly and turn dark brown to purplish-black. During periods of high humidity and leaf wetness, a cottony, white mold growth is usually visible on lower leaf surfaces at the edges of lesions. In dry weather, infected leaf tissues quickly dry up and the white mold growth disappears. Infected areas on stems appear brown to black and entire veins may be killed in a short time when moist weather persists.

Phylogenetic system of classification is based on evolutionary relationships. This phylogenetic classification system names only clades-groups of organisms that are all descended from a common ancestor. Under a system of phylogenetic classification, we could name any clade on this tree. For example, the Testudines, Squamata, Archosauria, and Crocodylomorpha all form clades.

Fucus belongs to class-Phaeophyceae, in which reserve food is found in form of laminarin, mannitol and oil.
Chara belongs to class- Chlorophyceae, in which reserve food is found in form of starch and oil.
Porphyra and Grachillaria belong to class- Rhodophyceae, in which reserve food is found in form of floridean starch and Galactan- SO₄ polymers

Single celled eukaryotes are included in protista. Protista includes all unicellular and colonial eukaryotes except green and red algae. It is also known as kingdom of unicellular eukaryotes.