Biological Classification

In Whittaker's five-kingdom classification, organization complexity increases from: C (Monera, unicellular prokaryote) \rightarrow E (Protista, unicellular eukaryote) \rightarrow A (Fungi, multicellular loose mycelium) \rightarrow D (Plantae, tissue/organ autotrophs) \rightarrow B (Animalia, tissue/organ/organ-system heterotrophs).

Whittaker's criteria were cell structure, body (thallus) organisation, mode of nutrition, reproduction and phylogenetic relationships.
Presence or absence of a well defined nucleus was not listed as a separate criterion.

R. H. Whittaker (1969) proposed the five kingdom classification: Monera, Protista, Fungi, Plantae and Animalia.
His criteria were cell structure (prokaryotic or eukaryotic), body organisation (unicellular or multicellular), mode of nutrition, reproduction and phylogenetic relationships.
Among these, the mode of nutrition is the main basis that separates the three multicellular kingdoms: Plantae (autotrophic, photosynthetic), Fungi (heterotrophic, absorptive) and Animalia (heterotrophic, ingestive).
So, as per the answer key, the main basis of the five kingdom system is nutrition.

A. Asexual reproduction in Phaeophyceae is usually by biflagellate zoospores – correct. B. Sexual reproduction may be isogamous, anisogamous or oogamous, not oogamous only – incorrect. C. Stored food is complex carbohydrates – mannitol or laminarin – correct. D. Major pigments are chlorophyll a, c, carotenoids and xanthophylls (fucoxanthin) – correct. E. Vegetative cells have a cellulosic wall usually covered on the outside by a gelatinous coating of algin – correct. So A, C, D and E only are correct.

(a) is correct: methanogens are archaebacteria; they live in marshy areas and in the gut of ruminants and produce methane.
(b) is correct: $Nostoc$ is a filamentous cyanobacterium (blue-green alga) that fixes atmospheric nitrogen in specialised cells called heterocysts.
(c) is wrong: chemosynthetic autotrophic bacteria oxidise inorganic substances such as nitrites, nitrates and ammonia and use the released energy for ATP production; they play a great role in recycling nutrients like nitrogen, phosphorus, iron and sulphur. They do not synthesise cellulose from glucose.
(d) is correct: mycoplasmas completely lack a cell wall, are the smallest living cells known and can survive without oxygen.
Hence the correct statements are (a), (b) and (d).

Hyperthermophiles grow at very high temperatures, and those that also tolerate a pH of about 2 are thermoacidophiles; they live in hot sulphur springs.
Such extreme habitats can be colonised only by prokaryotes.
Most thermoacidophiles are archaebacteria (archaea), e.g., $Sulfolobus$ and $Thermoplasma$; their special cell wall and branched-chain membrane lipids let them survive.
A few eubacteria (some thermophilic bacteria of hot springs) can also grow under such conditions.
Liverworts, mosses, yeasts, diatoms and protists are eukaryotes that cannot survive in such habitats.
Hence the two groups are eubacteria and archaea.

In oxygenic photosynthesis water is the hydrogen donor and oxygen is released: $6CO_2 + 12H_2O \rightarrow C_6H_{12}O_6 + 6H_2O + 6O_2$
Among prokaryotes it occurs only in cyanobacteria, which have chlorophyll a and both photosystems, like green plants.
$Oscillatoria$ is a cyanobacterium (blue-green alga).
$Chlorobium$ (green sulphur bacterium), $Chromatium$ (purple sulphur bacterium) and $Rhodospirillum$ (purple non-sulphur bacterium) carry out anoxygenic photosynthesis: they use $H_2S$ or organic compounds as the hydrogen donor and do not release oxygen.
Hence oxygenic photosynthesis occurs in $Oscillatoria$.

Alternaria is a deuteromycete (imperfect fungus) in which sexual reproduction is absent.
Phytophthora belongs to Phycomycetes; its mycelium is aseptate.
Mucor belongs to Zygomycetes; it reproduces by conjugation.
Agaricus belongs to Basidiomycetes; it is saprotrophic, not parasitic.

The cell wall of true fungi is made of chitin (fungal cellulose) and other polysaccharides.
Pythium belongs to the Oomycetes (water moulds), a group traditionally placed in Phycomycetes. Unlike other fungi, the cell wall of oomycetes is mainly made of cellulose and glucans, with little or no chitin.
Pythium causes the damping-off disease of seedlings.
Saccharomyces (yeast) is an ascomycete fungus; its cell wall has glucans, mannans and chitin, not cellulose.
Pseudomonas and Xanthomonas are bacteria; their cell walls are made of peptidoglycan (murein).
So cellulose is the major component of the cell wall of Pythium.

The class Basidiomycetes includes those fungi that produce their basidia and basidiospores on or in a fruiting body called the basidiocarp.
Commonly known forms are mushrooms, bracket fungi, puffballs, stinkhorns and bird's nest fungi; rusts and smuts also belong here.
Bird's nest fungi and puffballs are both basidiomycetes, so this pair is correct.
Claviceps, Peziza and Morchella are members of Ascomycetes (sac fungi), which produce ascospores inside asci.
So every other pair contains one ascomycete: puffballs with Claviceps, Peziza with stinkhorns, and Morchella with mushrooms.
The pair belonging to Basidiomycetes is bird's nest fungi and puffballs.

During storage of grains and seeds in warm, humid conditions, the mould Aspergillus flavus grows on groundnut, maize and other crops.
It secretes aflatoxins, which are highly toxic and carcinogenic (they damage the liver and cause liver cancer) to humans and animals.
Penicillium spoils stored fruits and is known for antibiotics, while Fusarium and Colletotrichum are mainly field pathogens.
So Aspergillus secretes toxins during storage of crop plants.

Euglenoid switches between photosynthetic and heterotrophic modes of nutrition (A-IV); Dinoflagellates are largely photosynthetic (B-III); Slime moulds are saprophytic (C-II); Plasmodium (sporozoan) is parasitic (D-I).

Cyanobacteria (e.g. Nostoc, Anabaena) possess specialised cells called heterocysts, which are the sites of nitrogen fixation — so the statement that they lack heterocysts is incorrect.

Gas vacuoles are inclusion bodies found in blue-green, purple and green photosynthetic bacteria, helping them float/regulate buoyancy in water.

Phycoerythrin is the major accessory pigment found in red algae (Rhodophyceae), giving them their characteristic red colour.

Mycoplasma (Pleuropneumonia-like organisms, PPLO) are the smallest living cells known, with a size of about 0.1 micrometer ($\mu m$).

Pseudopodia are locomotory structures in sarcodines (amoeboid protozoans), not in sporozoans. So the statement about pseudopodia in Sporozoans is wrong.

In $Agaricus$ (a genus of basidiomycetes), basidiospores (meiospores) are produced exogenously. $Neurospora$ (a genus of ascomycetes) produces ascospores as meiospores, but endogenously inside the ascus. $Alternaria$ (a genus of deuteromycetes) does not produce sexual spores. $Saccharomyces$ (unicellular ascomycete) produces ascospores endogenously.

Trypanosoma is a flagellated protozoan that causes sleeping sickness.
Noctiluca is a marine dinoflagellate known for bioluminescence; it is free-living.
Monocystis is a sporozoan that lives as a parasite in the seminal vesicles of the earthworm; it has no flagella in the adult stage.
Giardia is a flagellated protozoan that is parasitic in the human intestine.
Noctiluca is not a parasite, so they are not all parasites; Monocystis has no flagella, so they do not all have flagella; and only Monocystis is a typical spore producer.
All four are single-celled eukaryotes and belong to the kingdom Protista.
So what is common is that these are all unicellular protists.

Autotrophs prepare their own food either by photosynthesis or by chemosynthesis.
Photoautotrophs in the list: $Nostoc$ (a cyanobacterium), $Chara$ (a green alga), $Porphyra$ (a red alga) and $Wolffia$ (a tiny angiosperm).
Chemoautotrophs in the list: $Nitrosomonas$ and $Nitrobacter$ (nitrifying bacteria that obtain energy by oxidising ammonia and nitrite).
Heterotrophs in the list: $Lactobacillus$ (a lactic acid bacterium), $Streptomyces$ (a saprophytic actinomycete), $Saccharomyces$ (yeast, a fungus) and $Trypanosoma$ (a parasitic protozoan).
Number of autotrophs = 4 + 2 = 6.
So six organisms are autotrophs.

$Plasmodium$ (malaria) and $Trypanosoma$ (sleeping sickness) are protozoan parasites, but $Cuscuta$ is a parasitic flowering plant. So this set has exactly one exception and it is correctly named as $Cuscuta$.
Typhoid, pneumonia and diphtheria are all bacterial diseases, so diphtheria is not an exception.
UAA, UAG and UGA are all stop codons, so UAG is not an exception.
Kangaroo, koala and wombat are all Australian marsupials, so wombat is not an exception.
Hence the set with a genuine exception is $Plasmodium$, $Cuscuta$, $Trypanosoma$ – protozoan parasites – with $Cuscuta$ as the exception.

$Puccinia$ is the rust fungus (it causes rust of wheat); the smut fungus is $Ustilago$. Both are basidiomycetes, but the pair $Puccinia$ – smut is wrong.
$Cassia$ and gulmohur show imbricate aestivation of the corolla, so that pair is correct.
Guttation, the loss of water as droplets from the tips of leaves through hydathodes, is caused by root pressure, so that pair is correct.
In roots the protoxylem lies towards the periphery and the metaxylem towards the centre, i.e., the xylem is exarch, so that pair is correct.
Hence the wrongly matched pair is $Puccinia$ – smut.

Late blight of potato is caused by $Phytophthora\ infestans$.
$Alternaria\ solani$ causes early blight of potato, so this pairing is wrong.
Root-knot disease of vegetables is caused by the nematode $Meloidogyne$ (correct).
Black rust of wheat is caused by $Puccinia\ graminis\ tritici$ (correct).
Loose smut of wheat is caused by $Ustilago\ nuda$ (correct).
Hence the wrong pairing is late blight of potato : $Alternaria\ solani$.

Carl Woese proposed the three domain system (Bacteria, Archaea and Eukarya) on the basis of differences in 16S ribosomal RNA sequences.
Archaea are prokaryotic in organisation: they have no nucleus and no membrane-bound organelles, so they do not completely differ from prokaryotes.
They resemble eukaryotes in some features of their genetic machinery, such as histone-like proteins, RNA polymerase and the initiation of translation, but they do not resemble eukarya in all respects.
They also have some novel features of their own: membrane lipids with branched chains joined to glycerol by ether linkages, cell walls without peptidoglycan (murein), and unique pathways such as methanogenesis.
These novel features, which are absent in bacteria as well as in eukaryotes, allow them to live in extreme habitats such as hot springs, salty areas and marshy areas.
So the true statement is that archaea have some novel features that are absent in other prokaryotes and eukaryotes.

Peritrichous flagellation means that the flagella are distributed all over the surface of the bacterial cell; Escherichia coli has peritrichous flagella. So A - L.
Ginkgo biloba is called a living fossil because it has survived almost unchanged since the Mesozoic era. So B - J.
Rhizophores are leafless, colourless downward-growing branches that bear roots at their tips; they are found in Selaginella. So C - M.
Wolffia, a tiny floating duckweed of family Lemnaceae, is the smallest flowering plant. So D - N.
Macrocystis, a brown alga (kelp), is the largest perennial alga, reaching lengths of about 60 m. So E - K.
Correct match: A-L, B-J, C-M, D-N, E-K.

The prefix 'baro' refers to pressure, not to barium.
Barophilic (piezophilic) prokaryotes are micro-organisms that grow best at high hydrostatic pressure.
Such pressures are found in the deep oceans, so barophiles grow and multiply in very deep marine sediments and deep sea waters, where the pressure may be hundreds of atmospheres.
Their membranes and enzymes are adapted to work under these pressures.
They have nothing to do with barium salts, and organisms of alkaline frozen lakes would be alkaliphiles and psychrophiles.
So barophilic prokaryotes grow and multiply in very deep marine sediments.

Tobacco mosaic virus (TMV), the first virus to be discovered and crystallised (Stanley, 1935), is a rod-shaped (helical) virus.
It is about 300 nm long and about 18 nm in diameter (often rounded to 20 nm).
It consists of a single strand of RNA (about 6400 nucleotides) wound in a helix, surrounded by about 2130 identical protein subunits (capsomeres).
So TMV is a tubular filament of size about 300 × 20 nm.

Loose smut of wheat is caused by the fungus Ustilago tritici (U. nuda tritici).
Its spores are carried by wind to healthy wheat flowers at flowering time. The fungus infects the flower and the developing grain, and remains dormant inside the embryo of the seed (internally seed-borne).
When the infected seed is sown, the fungus grows with the plant and replaces the ears with masses of black spores.
Covered smut of barley is externally seed-borne (spores on the seed surface), corn stunt is caused by a spiroplasma, and soft rot of potato by bacteria.
So loose smut of wheat spreads by seed and flowers.

'Photo' means that the energy source is light (radiation). 'Litho' means that the hydrogen (electron) donor is an inorganic compound.
Photolithotrophs obtain energy from light and hydrogen from inorganic substances such as $H_2O$ (green plants, cyanobacteria) or $H_2S$ (green and purple sulphur bacteria).
Photo-organotrophs use organic compounds as the hydrogen donor (e.g. purple non-sulphur bacteria).
So photolithotrophs obtain energy from radiation and hydrogen from inorganic compounds.

Most plant viruses (e.g. TMV) have single-stranded RNA.
Cauliflower mosaic virus (CaMV) is an exception: its genome is double-stranded DNA, which it replicates through an RNA intermediate (reverse transcription).
Its 35S promoter is widely used in plant genetic engineering.
So cauliflower mosaic virus contains ds DNA.

Cyanobacteria (blue-green algae) carry out oxygenic photosynthesis like plants: they use water as the electron donor and release oxygen.
Many of them (e.g. Nostoc, Anabaena) also fix atmospheric nitrogen using the enzyme nitrogenase, usually in special cells called heterocysts, which protect nitrogenase from oxygen.
So cyanobacteria are oxygenic with nitrogenase.

Many parasitic fungi form an adhesive pad (appressorium) on the host surface.
From it, a fine infection peg pierces the host cuticle and cell wall. This uses both mechanical pressure (high turgor pressure in the appressorium) and enzymes (cutinases and cellulases that soften the wall).
So the adhesive pad penetrates the host with the help of mechanical pressure and enzymes.