Grade 11 : Biology - Biological Classification (Set 3)

Explanation: Whittaker's major classification criteria included cell structure, body organisation, mode of nutrition, reproduction, and phylogenetic relationships. Organellar ribosome density (70S vs 80S fine sub-unit detail) was not an explicit classification criterion in his 1969 five-kingdom framework.

Explanation: Methanogens are obligate anaerobes (they live in strict absence of oxygen), not obligate aerobes. They produce methane in anaerobic environments like ruminant digestive tracts and marshes.

Explanation: Nostoc and Anabaena possess specialized cells called heterocysts which create anaerobic micro-environments necessary for the functioning of the nitrogenase enzyme during atmospheric nitrogen fixation.

Explanation: Diatom cell walls form two thin overlapping shells fitted like a soap box, embedded with silica ($SiO_2$). This makes the cell walls indestructible, leading to diatomaceous earth accumulation over millions of years.

Explanation: Red dinoflagellates such as Gonyaulax undergo rapid multiplication, coloring the sea red and releasing toxins (saxitoxins) that can kill marine animals like fish.

Explanation: Euglenoids lack a cell wall and instead possess a flexible protein-rich outer layer called a pellicle, allowing their body to flex and maneuver smoothly.

Explanation: Under suitable conditions, slime moulds form an aggregation called Plasmodium which spreads over decay materials. Under unfavorable conditions, it differentiates to form spore-bearing fruiting bodies.

Explanation: Sporozoans include diverse organisms that have an infectious spore-like stage in their life cycle. Plasmodium (malarial parasite) is the classic example. Trypanosoma is flagellated, while Paramecium is ciliated.

Explanation: Both statements are factually correct. Fungal cell walls consist of chitin and polysaccharides, and unseptate continuous hyphae with multiple nuclei are called coenocytic hyphae.

Explanation: Deuteromycetes are called imperfect fungi because only their asexual or vegetative phases are known. When sexual forms are discovered, they are moved to Ascomycetes or Basidiomycetes.

Explanation: In Phycomycetes (e.g., Rhizopus, Mucor), asexual reproduction takes place by motile zoospores or non-motile aplanospores formed endogenously inside a sporangium.

Explanation: Neurospora crassa (an ascomycete) is widely used in biochemical and genetic work due to its rapid haploid life cycle and ease of culturing.

Explanation: In Basidiomycetes, karyogamy and meiosis take place inside the basidium, producing 4 basidiospores exogenously on the basidium tip.

Explanation: The life cycle of plants involves alternating haploid gamete-producing gametophytic and diploid spore-producing sporophytic phases, known as alternation of generations.

Explanation: Kingdom Animalia comprises heterotrophic, eukaryotic, multicellular organisms whose cells completely lack cell walls and ingest food (holozoic nutrition).

Explanation: M.W. Beijerinck in 1898 showed that tobacco mosaic extract was infectious and called the living infectious fluid Contagium vivum fluidum.

Explanation: Discovered by T.O. Diener in 1971, viroids are smaller than viruses and consist of free, low-molecular-weight RNA without any protein coat (capsid).

Explanation: Prions are infectious agents composed of abnormally folded proteins. They transmit neurological disorders such as BSE in cattle and Cr-Jacob disease (CJD) in humans.

Explanation: In lichens, the autotrophic algal component is the Phycobiont and the heterotrophic fungal component is the Mycobiont.

Explanation: Mycoplasma are the smallest known living cells. They completely lack a cell wall, are pleomorphic, can survive without oxygen, and many are pathogenic in animals and plants.