Chapter 2: Biological Classification Short Questions | biology Class 11 CBSE

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Chapter 2: Biological Classification Short Questions | biology Class 11 CBSE | ByteNotes.in

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Question 1

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Why was the Two Kingdom classification system considered inadequate?

It failed to distinguish between prokaryotic organisms (bacteria, cyanobacteria) and eukaryotic organisms, placing them all under Plantae based solely on the presence of a cell wall.
It grouped together unicellular and multicellular organisms (e.g., Chlamydomonas and Spirogyra) without recognising their fundamental differences in body organisation.
It did not differentiate between the heterotrophic fungi and autotrophic green plants, even though their cell wall compositions — chitin versus cellulose — are fundamentally different.

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Question 2

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Name the four shapes of bacteria and give one example of each.

Coccus (pl.: cocci) — spherical in shape; example: Staphylococcus.
Bacillus (pl.: bacilli) — rod-shaped; example: Bacillus anthracis.
Vibrio (pl.: vibrio) — comma-shaped; example: Vibrio cholerae.

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Question 3

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What are heterocysts and what is their function in cyanobacteria?

Heterocysts are specialised cells found in certain filamentous cyanobacteria such as Nostoc and Anabaena.
They are the sites of atmospheric nitrogen fixation, converting free nitrogen gas into a form that can be used by organisms.
Their specialised structure provides an anaerobic microenvironment essential for the functioning of the nitrogen-fixing enzyme nitrogenase.

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Question 4

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How do Archaebacteria differ from other bacteria in terms of habitat and cell wall?

Archaebacteria inhabit extremely harsh environments such as highly saline areas (halophiles), hot springs (thermoacidophiles), and marshy, anaerobic areas (methanogens).
They possess a unique cell wall structure that is chemically different from the cell walls of other bacteria, which is the primary reason for their survival in extreme conditions.
Unlike eubacteria that have cell walls made of peptidoglycan, archaebacterial cell walls lack this component, making them more resistant to environmental extremes.

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Question 5

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What is the role of methanogens in relation to ruminant animals?

Methanogens are a type of Archaebacteria that live in the gut of ruminant animals such as cows and buffaloes.
They break down organic matter in the animal's digestive tract and produce methane (biogas) as a metabolic byproduct.
This methane is released from the dung of these animals and can be harvested as a renewable source of biogas energy.

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Question 6

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What is Mycoplasma? State two characteristics that make it unique among bacteria.

Mycoplasma are organisms belonging to Kingdom Monera that completely lack a cell wall, making them distinct from all other bacteria.
They are the smallest living cells known and are capable of surviving without oxygen (anaerobic).
Many mycoplasmas are pathogenic, causing diseases in both animals and plants.

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Question 7

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Explain the significance of diatomaceous earth.

Diatomaceous earth is the accumulated deposit of indestructible silica-embedded cell walls of diatoms, built up over billions of years in aquatic habitats.
Because the silica walls of diatoms are indestructible and leave behind large deposits, these form gritty geological strata known as diatomaceous earth.
This material has commercial uses — it is used in polishing products and in the filtration of oils and syrups due to its abrasive and porous nature.

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Question 8

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What is the phenomenon of 'red tides' and which organism causes it?

Red tides is a phenomenon where the sea appears red due to the explosive multiplication of red-pigmented dinoflagellates such as Gonyaulax.
The rapid proliferation of these organisms produces massive blooms that colour the water red, orange, or brown depending on the dominant pigments.
Toxins released by these large numbers of dinoflagellates can be lethal to other marine animals, including fish, causing widespread marine mortality.

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Question 9

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Why are Euglenoids considered a connecting link between plants and animals?

Euglenoids are photosynthetic in the presence of sunlight, behaving like autotrophic plants and possessing pigments identical to those found in higher plants.
When deprived of sunlight, they switch to a heterotrophic mode of nutrition by predating on other smaller organisms, a behaviour typical of animals.
Instead of a cell wall, they have a protein-rich pellicle, making them structurally different from plants while their dual nutrition mode bridges the plant-animal divide.

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Question 10

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Describe the structure and life cycle stage of slime mould plasmodium.

Plasmodium in slime moulds is an aggregation of cells that forms under suitable environmental conditions and can grow and spread over several feet.
During unfavourable conditions, the plasmodium differentiates into fruiting bodies that bear spores at their tips; these spores have true walls.
The spores are highly resistant, survive for many years under adverse conditions, and are dispersed by air currents to colonise new habitats.

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Question 11

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State the main criteria used by Whittaker for Five Kingdom Classification.

Whittaker used cell structure (prokaryotic vs. eukaryotic, presence/absence of cell wall and its composition) as a primary criterion.
Body organisation (cellular, tissue, organ, organ-system level) and mode of nutrition (autotrophic vs. heterotrophic, photosynthetic vs. chemosynthetic vs. holozoic) were key distinguishing features.
Phylogenetic relationships (evolutionary history and relatedness) and mode of reproduction were also considered to reflect natural evolutionary groupings.

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Question 12

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What are coenocytic hyphae? In which class of fungi are they found?

Coenocytic hyphae are continuous, aseptate (without cross walls) fungal filaments filled with multinucleated cytoplasm.
Unlike septate hyphae, coenocytic hyphae form a single continuous multinucleate mass of cytoplasm without being divided into individual cells.
They are found in Phycomycetes (e.g., Mucor and Rhizopus), where the aseptate, coenocytic mycelium is a defining characteristic of this class.

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Question 13

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What is a dikaryon and what is the dikaryophase in fungi?

A dikaryon is a fungal cell or hypha that contains two genetically distinct haploid nuclei (n+n) per cell, arising after plasmogamy but before karyogamy.
The dikaryophase is the phase in the life cycle of ascomycetes and basidiomycetes during which this dikaryotic (n+n) condition persists.
This phase is significant because it delays nuclear fusion, allowing the two parental genomes to coexist and replicate together before ultimately undergoing karyogamy.

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Chapter 2: Biological Classification | Short Questions

Why was the Two Kingdom classification system considered inadequate?

Name the four shapes of bacteria and give one example of each.

What are heterocysts and what is their function in cyanobacteria?

How do Archaebacteria differ from other bacteria in terms of habitat and cell wall?

What is the role of methanogens in relation to ruminant animals?

What is Mycoplasma? State two characteristics that make it unique among bacteria.

Explain the significance of diatomaceous earth.

What is the phenomenon of 'red tides' and which organism causes it?

Why are Euglenoids considered a connecting link between plants and animals?

Describe the structure and life cycle stage of slime mould plasmodium.

State the main criteria used by Whittaker for Five Kingdom Classification.

What are coenocytic hyphae? In which class of fungi are they found?

What is a dikaryon and what is the dikaryophase in fungi?

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