Biological Classification Class 11 Biology: Five Kingdoms, Viruses and Lichens

What Biological Classification is about

Weightage: This chapter is part of Unit I, Diversity of Living Organisms, which carries 15 of the 70 theory marks in the school annual exam together with The Living World, Plant Kingdom and Animal Kingdom.Source: CBSE Biology (044) syllabus 2026-27, Class XI course structure, Unit I Diversity of Living Organisms

Key concepts

From two kingdoms to five kingdoms

NCERT section Introduction (two-kingdom and five-kingdom systems)

Aristotle first classified plants (trees, shrubs, herbs) and animals (with and without red blood). Linnaeus used a two-kingdom system: Plantae and Animalia.

Problems with two kingdoms:

• It did not separate prokaryotes (bacteria, cyanobacteria) from eukaryotes.
• It grouped unicellular and multicellular organisms together.
• It grouped photosynthetic (green algae) and non-photosynthetic (fungi) organisms together under plants, although fungi have chitin walls and are heterotrophs.

Whittaker's five-kingdom system (1969): Monera, Protista, Fungi, Plantae, Animalia. Criteria:
1. Cell structure (prokaryotic or eukaryotic).
2. Body organisation (unicellular, multicellular; tissue level).
3. Mode of nutrition (autotrophic or heterotrophic; saprophytic, parasitic, holozoic).
4. Reproduction.
5. Phylogenetic (evolutionary) relationships.

The cell wall composition also differs: peptidoglycan (Monera), cellulose (Plantae), chitin (Fungi), absent (Animalia; varies in Protista). A three-domain system has also been proposed, splitting Monera into two domains (Bacteria and Archaea) and putting the eukaryotic kingdoms in the third, giving six kingdoms.

Worked example

Give two drawbacks of the two-kingdom classification and name the five criteria Whittaker used. (3 marks)

Try it first, then show the solutionSolution

1. Drawbacks (any two): did not separate prokaryotes from eukaryotes; grouped unicellular with multicellular; grouped photosynthetic algae with non-photosynthetic fungi. (1)
2. Criteria: cell structure, body organisation, mode of nutrition, reproduction, phylogenetic relationships. (2)

Answer: Two-kingdom mixed prokaryotes with eukaryotes and fungi with plants; Whittaker used cell structure, body organisation, nutrition, reproduction and phylogeny.

Kingdom Monera: bacteria

NCERT section 2.1 Kingdom Monera (2.1.1 Archaebacteria, 2.1.2 Eubacteria)

Monera are prokaryotes (no membrane-bound nucleus or organelles); the cell wall is mainly peptidoglycan. Bacteria are found almost everywhere: hot springs, deserts, snow, deep oceans, and as parasites or symbionts.

Shapes: spherical (coccus), rod-shaped (bacillus), comma-shaped (vibrium) and spiral (spirillum).

Bacteria show the most extensive metabolic diversity of all groups:

Archaebacteria live in the harshest habitats because their cell wall structure is different:

• Halophiles: extremely salty areas.
• Thermoacidophiles: hot springs.
• Methanogens: marshy areas and the gut of ruminants (cows, buffaloes); they produce methane (biogas) from cow dung.

Eubacteria ('true bacteria') have a rigid cell wall and, if motile, a flagellum.

• Photosynthetic autotrophs: cyanobacteria (blue-green algae) have chlorophyll a like plants; unicellular, colonial or filamentous; often surrounded by a gelatinous sheath; may form blooms in polluted water. Some, like *Nostoc* and *Anabaena*, have heterocysts that fix atmospheric nitrogen.
• Chemosynthetic autotrophs oxidise inorganic substances (nitrates, nitrites, ammonia) to get energy; they help recycle nitrogen, phosphorus, iron and sulphur.
• Heterotrophic bacteria are the most abundant: decomposers; useful in curd making, antibiotic production and nitrogen fixation in legumes; harmful ones cause cholera, typhoid, tetanus and citrus canker.

Reproduction: mainly fission; spores in unfavourable conditions; a primitive DNA transfer resembling sexual reproduction.

Mycoplasma: organisms with no cell wall; the smallest living cells known; can survive without oxygen; many are pathogenic in animals and plants.

Worked example

Why can archaebacteria survive in extreme habitats? Name their three groups with one habitat each, and give one use of methanogens. (3 marks)

Try it first, then show the solutionSolution

1. Their cell wall structure differs from other bacteria, which helps them survive extreme conditions. (1)
2. Halophiles (salty areas), thermoacidophiles (hot springs), methanogens (marshes, gut of ruminants). (1½)
3. Methanogens produce methane (biogas) from cow dung. (½)

Answer: Special cell wall; halophiles, thermoacidophiles, methanogens; biogas production.

Kingdom Protista: chrysophytes, dinoflagellates and euglenoids

NCERT section 2.2 Kingdom Protista (2.2.1 Chrysophytes, 2.2.2 Dinoflagellates, 2.2.3 Euglenoids)

Protista are single-celled eukaryotes, mostly aquatic. Their boundaries are not well defined (a photosynthetic protist for one biologist may be a plant for another). They have a well-defined nucleus and membrane-bound organelles; some have flagella or cilia. They reproduce asexually and sexually (cell fusion and zygote formation). Protists link plants, animals and fungi.

Chrysophytes: diatoms and golden algae (desmids), in fresh water and the sea; microscopic, float passively (plankton); mostly photosynthetic. Diatom cell walls form two thin overlapping shells that fit like a soap box, and are embedded with silica, so they are indestructible. Their accumulated walls form 'diatomaceous earth', used in polishing and in filtering oils and syrups. Diatoms are the chief producers of the oceans.

Dinoflagellates: mostly marine, photosynthetic; yellow, green, brown, blue or red depending on pigments. The cell wall has stiff cellulose plates. Most have two flagella: one longitudinal, one transverse in a furrow between the plates. Red dinoflagellates (*Gonyaulax*) multiply rapidly and make the sea look red (red tides); their toxins may kill fish.

Euglenoids: mostly found in stagnant fresh water. They have no cell wall; a protein-rich covering called the pellicle lets the body bend and change shape. Two flagella (one short, one long). Photosynthetic in sunlight, but behave like heterotrophs (predators) when deprived of light. Their pigments are identical to those of higher plants. Example: *Euglena*.

Worked example

Explain why (a) diatom walls do not decay, (b) the sea sometimes turns red, (c) Euglena is called a link between plants and animals. (3 marks)

Try it first, then show the solutionSolution

1. (a) Diatom walls are embedded with silica, which makes them indestructible; they pile up as diatomaceous earth. (1)
2. (b) Red dinoflagellates such as Gonyaulax multiply rapidly (red tide); their toxins may kill fish. (1)
3. (c) Euglena photosynthesises in light (plant-like) but feeds heterotrophically in darkness and has a flexible pellicle instead of a cell wall (animal-like). (1)

Answer: (a) silica (b) Gonyaulax bloom (c) both autotrophic and heterotrophic, with a pellicle

Kingdom Protista: slime moulds and protozoans

NCERT section 2.2.4 Slime Moulds; 2.2.5 Protozoans

Slime moulds are saprophytic protists that creep over rotting leaves and twigs, swallowing organic matter as they go. In suitable conditions they form an aggregation called a plasmodium, which may grow and spread over several feet. In unfavourable conditions the plasmodium forms fruiting bodies bearing spores at their tips. The spores have true walls, are extremely resistant and survive for many years; they are dispersed by air currents.

Protozoans are heterotrophs (predators or parasites), believed to be primitive relatives of animals. Four groups:
1. Amoeboid protozoans: fresh water, sea or moist soil; move and capture prey with pseudopodia (false feet), e.g. *Amoeba*. Marine forms have silica shells. Some, like *Entamoeba*, are parasites.
2. Flagellated protozoans: free-living or parasitic, with flagella. Parasites cause diseases such as sleeping sickness, e.g. *Trypanosoma*.
3. Ciliated protozoans: aquatic, actively moving with thousands of cilia; a cavity (gullet) opens to the outside, and coordinated cilia beat water laden with food into it, e.g. *Paramoecium*.
4. Sporozoans: an infectious spore-like stage in the life cycle; the most notorious is *Plasmodium* (malarial parasite), which has had a staggering effect on human population.

Worked example

A pond-water sample under the microscope shows: (i) a cell covered with thousands of hair-like structures that sweep food into a cavity, (ii) a cell that changes shape and pushes out finger-like projections to engulf food. A blood smear from a feverish patient shows (iii) a parasite with no locomotory organelles. Name the protozoan group and a likely genus for each, and state the feature that helps each group move or infect. (3 marks)

Try it first, then show the solutionSolution

1. (i) Ciliated protozoan, Paramoecium: cilia beat in a coordinated way and drive food-laden water into the gullet. (1)
2. (ii) Amoeboid protozoan, Amoeba: pseudopodia (false feet) for movement and capturing prey. (1)
3. (iii) Sporozoan, Plasmodium (malarial parasite): it has an infectious spore-like stage in its life cycle. The fourth group, flagellated protozoans such as Trypanosoma, moves by flagella. (1)

Answer: (i) ciliated, Paramoecium, cilia (ii) amoeboid, Amoeba, pseudopodia (iii) sporozoan, Plasmodium, infectious spore-like stage

Kingdom Fungi: general features

NCERT section 2.3 Kingdom Fungi (general features)

Fungi are heterotrophic eukaryotes with a wide range of form and habitat: mushrooms, moulds on bread and oranges, yeast for bread and beer, rusts and smuts on crops, *Puccinia* (wheat rust), and *Penicillium*, a source of antibiotics. They prefer warm, humid places (which is why food is kept in the fridge).

Structure: except unicellular yeasts, fungi are filamentous. The body is made of long, slender threads called hyphae; the network of hyphae is the mycelium. Some hyphae are continuous tubes filled with many nuclei (coenocytic, multinucleate); others have septae (cross walls). The cell wall is made of chitin and polysaccharides.

Nutrition: mostly saprophytes (absorb soluble organic matter from dead substrates); some are parasites on plants and animals; some are symbionts: with algae as lichens and with roots of higher plants as mycorrhiza.

Reproduction:

• Vegetative: fragmentation, fission, budding.
• Asexual: spores called conidia, sporangiospores or zoospores.
• Sexual: oospores, ascospores and basidiospores, produced in distinct structures called fruiting bodies.

The sexual cycle has three steps:
1. Plasmogamy: fusion of protoplasms of two motile or non-motile gametes.
2. Karyogamy: fusion of the two nuclei.
3. Meiosis in the zygote, giving haploid spores.
In ascomycetes and basidiomycetes, an intervening dikaryotic stage (n + n, two nuclei per cell, the dikaryophase) occurs between plasmogamy and karyogamy.

Worked example

Explain the terms (a) coenocytic hypha (b) dikaryon (c) mycorrhiza. (3 marks)

Try it first, then show the solutionSolution

1. (a) A hypha without septa: a continuous tube with many nuclei in common cytoplasm. (1)
2. (b) A cell with two separate haploid nuclei (n + n), formed after plasmogamy and before karyogamy in ascomycetes and basidiomycetes. (1)
3. (c) A symbiotic association of a fungus with the roots of a higher plant. (1)

Answer: (a) aseptate multinucleate hypha (b) n + n cell (c) fungus–root symbiosis

Classes of fungi

NCERT section 2.3.1 Phycomycetes; 2.3.2 Ascomycetes; 2.3.3 Basidiomycetes; 2.3.4 Deuteromycetes

Fungi are classified by the morphology of the mycelium, the mode of spore formation and the fruiting bodies.

1. Phycomycetes: in aquatic habitats, on decaying wood in moist places, or as obligate parasites on plants. Mycelium aseptate and coenocytic. Asexual: zoospores (motile) or aplanospores (non-motile), formed endogenously in a sporangium. Sexual: zygospore by fusion of two gametes (isogamous, anisogamous or oogamous). Examples: *Mucor*, *Rhizopus* (bread mould), *Albugo* (parasite on mustard).
2. Ascomycetes (sac fungi): mostly multicellular (*Penicillium*), rarely unicellular (yeast); saprophytic, decomposers, parasitic or coprophilous (growing on dung). Mycelium branched and septate. Asexual spores: conidia, produced exogenously on conidiophores. Sexual spores: ascospores, produced endogenously in sac-like asci, arranged in fruiting bodies called ascocarps. Examples: *Aspergillus*, *Claviceps*, *Neurospora* (used in biochemical and genetic work); morels and truffles are edible delicacies.
3. Basidiomycetes: mushrooms, bracket fungi, puffballs; in soil, on logs and tree stumps, and as plant parasites (rusts and smuts). Mycelium branched and septate. Asexual spores are generally absent; vegetative reproduction by fragmentation is common. Sex organs are absent, but plasmogamy occurs by fusion of two vegetative or somatic cells of different strains, forming a basidium. Karyogamy and meiosis in the basidium give four basidiospores, produced exogenously on the basidium, arranged in basidiocarps. Examples: *Agaricus* (mushroom), *Ustilago* (smut), *Puccinia* (rust fungus).
4. Deuteromycetes ('fungi imperfecti'): only asexual or vegetative phases are known. When the sexual stage is discovered, they are moved to ascomycetes or basidiomycetes. Mycelium septate and branched. Reproduce only by conidia. Some are saprophytes or parasites; many are decomposers that help mineral cycling. Examples: *Alternaria*, *Colletotrichum*, *Trichoderma*.

Worked example

Identify the class of each fungus and give one example: (a) aseptate, coenocytic mycelium; zoospores formed in sporangia; zygospores after sexual fusion (b) septate mycelium; no asexual spores; sexual spores formed outside club-shaped cells in a large fruiting body (c) septate mycelium; conidia on conidiophores; sexual spores inside sac-like cells. (3 marks)

Try it first, then show the solutionSolution

1. (a) Phycomycetes, e.g. Albugo, Mucor or Rhizopus. (1)
2. (b) Basidiomycetes: the club-shaped cells are basidia bearing basidiospores exogenously, in a basidiocarp; e.g. Agaricus. (1)
3. (c) Ascomycetes: ascospores form endogenously in asci; e.g. Aspergillus, Penicillium or Neurospora. (1)

Answer: (a) phycomycetes (Albugo) (b) basidiomycetes (Agaricus) (c) ascomycetes (Aspergillus)

Kingdoms Plantae and Animalia

NCERT section 2.4 Kingdom Plantae; 2.5 Kingdom Animalia

Plantae: all eukaryotic, chlorophyll-containing organisms (plants). A few are partially heterotrophic: insectivorous plants such as bladderwort and Venus fly trap, and parasites such as *Cuscuta*. Cells have a cellulose cell wall and chloroplasts. Includes algae, bryophytes, pteridophytes, gymnosperms and angiosperms. The life cycle shows alternation of generations between a diploid sporophytic and a haploid gametophytic phase (the details are not part of the 2026-27 syllabus).

Animalia: heterotrophic eukaryotes, multicellular, with no cell walls. They depend on plants directly or indirectly for food and digest it in an internal cavity (holozoic nutrition). Food reserves are stored as glycogen or fat. They follow a definite growth pattern into adults of definite shape and size. Higher forms have elaborate sensory and neuromotor mechanisms, and most can move. Sexual reproduction is by copulation of male and female, followed by embryological development.

Worked example

Cuscuta and the Venus fly trap are plants, though they obtain nourishment from other organisms. Explain how each feeds and why they are still placed in Plantae. (2 marks)

Try it first, then show the solutionSolution

1. Cuscuta is a parasite that absorbs food from its host plant; the Venus fly trap catches insects to obtain nitrogen. (1)
2. Both are eukaryotes with cellulose cell walls and other plant features (the fly trap is green and photosynthesises), so they belong to Plantae as partially heterotrophic members. (1)

Answer: Partial heterotrophs (parasite and insectivore) but with plant cell organisation.

Viruses, viroids, prions and lichens

NCERT section 2.6 Viruses, Viroids, Prions and Lichens

Whittaker's scheme does not include these.

Viruses: non-cellular organisms with an inert crystalline structure outside the living cell. Once they infect a cell they take over its machinery to replicate, killing the host. So are they living? Debatable.

• History: Dmitri Ivanowsky (1892) found that the agent of mosaic disease of tobacco was smaller than bacteria (it passed through bacteria-proof filters). M.W. Beijerinck (1898) showed that extract of infected plants could infect healthy plants and called the fluid *contagium vivum fluidum* (infectious living fluid). W.M. Stanley (1935) showed that viruses can be crystallised, and the crystals consist largely of proteins.
• Structure: genetic material (DNA or RNA, never both) surrounded by a protein coat, the capsid, made of subunits called capsomeres arranged in helical or polyhedral form. Plant viruses usually have single-stranded RNA; animal viruses single- or double-stranded RNA or double-stranded DNA; bacterial viruses (bacteriophages) usually double-stranded DNA.
• Diseases: mumps, smallpox, herpes, influenza, AIDS in humans; mosaic formation, leaf rolling and curling, yellowing and vein clearing, dwarfing and stunted growth in plants.

Viroids: discovered by T.O. Diener (1971) as the cause of potato spindle tuber disease. They are free RNA without a protein coat; the RNA has low molecular weight.

Prions: infectious agents consisting of abnormally folded protein, similar in size to viruses. They cause neurological diseases: bovine spongiform encephalopathy (BSE, mad cow disease) in cattle and its human analogue, Creutzfeldt-Jakob disease (CJD).

Lichens: symbiotic (mutually useful) associations between algae (phycobiont) and fungi (mycobiont). The alga makes food for the fungus; the fungus gives shelter and absorbs mineral nutrients and water for the alga. They are so closely associated that they look like one organism. Lichens are very good pollution indicators: they do not grow in polluted areas.

Worked example

A plant pathologist isolates three infectious agents: X is nucleic acid wrapped in a protein coat, Y is a small RNA molecule with no coat, and Z contains no nucleic acid at all. Name each type of agent and one disease caused by each. Which of them was first shown to pass through bacteria-proof filters? (3 marks)

Try it first, then show the solutionSolution

1. X is a virus (nucleic acid inside a capsid), e.g. tobacco mosaic disease in plants or influenza in humans. (1)
2. Y is a viroid (free low-molecular-weight RNA), e.g. potato spindle tuber disease; Z is a prion (abnormally folded protein), e.g. BSE in cattle or CJD in humans. (1)
3. The virus: Ivanowsky (1892) found that the agent of tobacco mosaic disease passed through filters that stop bacteria. (1)

Answer: X virus (tobacco mosaic), Y viroid (potato spindle tuber), Z prion (BSE/CJD); the virus was the agent shown to pass bacteria-proof filters.

Biological Classification in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Kingdom Fungi: Classes and Reproduction
• Kingdom Monera: Bacteria

Biological Classification: key facts

Five kingdoms

$\text{Monera},\text{Protista},\text{Fungi},\text{Plantae},\text{Animalia}$

Whittaker (1969).

Whittaker's criteria

$\text{cell structure},\text{body organisation},\text{nutrition},\text{reproduction},\text{phylogeny}$

Five criteria for five kingdoms.

Sexual cycle in fungi

$\text{plasmogamy}\to (\text{dikaryophase }n+n)\to \text{karyogamy}\to \text{meiosis}$

Dikaryophase only in ascomycetes and basidiomycetes.

Cell wall materials

$\text{Monera: peptidoglycan};\text{Fungi: chitin};\text{Plantae: cellulose};\text{Animalia: none}$

Protista vary (silica shells, cellulose plates, pellicle).

Virus structure

$\text{virus}=\text{nucleic acid (DNA or RNA)}+\text{capsid (capsomeres)}$

Viroid = RNA only; prion = protein only.

Biological Classification: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Biological Classification

The question patterns to expect, and the method that works for each.

Tricks to remember Biological Classification

Short memory aids. Say each one aloud once, then use it on a question the same day.

• My Pet Frog Plays Alone

  Monera, Protista, Fungi, Plantae, Animalia.

  Use it when: Listing the five kingdoms in order.

• HTM extremists

  Halophiles (salt), Thermoacidophiles (hot springs), Methanogens (marsh, rumen).

  Use it when: Archaebacteria groups.

• PAB-D fungi

  Phycomycetes (Mucor, Rhizopus, Albugo); Ascomycetes (Aspergillus, Claviceps, Neurospora); Basidiomycetes (Agaricus, Ustilago, Puccinia); Deuteromycetes (Alternaria, Colletotrichum, Trichoderma).

  Use it when: Examples of fungal classes.

• A-F-C-S protozoa

  Amoeboid (Amoeba), Flagellated (Trypanosoma), Ciliated (Paramoecium), Sporozoans (Plasmodium).

  Use it when: Protozoan groups.

• I-B-S-D for virus history

  Ivanowsky 1892 (filters), Beijerinck 1898 (living fluid), Stanley 1935 (crystals), Diener 1971 (viroids).

  Use it when: History questions.

Biological Classification: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section E style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 4-mark question split into 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Biological Classification

The slips examiners see most often, and what to write instead.

• ✗Mistake: Calling cyanobacteria algae in the five-kingdom system

  Their old name is blue-green algae.

  ✓Do this: Cyanobacteria are prokaryotes in Monera, not algae.

  Usually costs: 1 mark.

• ✗Mistake: Saying basidiomycetes form conidia

  Ascomycete features are mixed in.

  ✓Do this: Basidiomycetes generally lack asexual spores; ascomycetes and deuteromycetes form conidia.

  Usually costs: 1 mark.

• ✗Mistake: Mixing up endogenous and exogenous spores

  Ascospores and basidiospores are confused.

  ✓Do this: Ascospores form inside asci (endogenous); basidiospores form on basidia (exogenous).

  Usually costs: 1 mark.

• ✗Mistake: Writing that viroids have a protein coat

  They are treated as small viruses.

  ✓Do this: Viroids are naked RNA; prions are protein only.

  Usually costs: 1 mark.

• ✗Mistake: Wrong cell-wall material

  Students write cellulose for fungi.

  ✓Do this: Fungi: chitin; plants: cellulose; bacteria: peptidoglycan; diatoms: silica.

  Usually costs: 1 mark.

NCERT exercise guide: Biological Classification

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

Practice questions on Biological Classification

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   Which of the following lacks a cell wall?
   (a) Nostoc (b) Mycoplasma (c) Anabaena (d) Rhizopus

   Hint

   Smallest living cells.

   Answer

   (b) Mycoplasma

2. Q2 · 1 mark · MCQExam level

   Ascospores are produced:
   (a) exogenously on basidia (b) endogenously in asci (c) in sporangia (d) on conidiophores

   Hint

   Sac fungi.

   Answer

   (b) endogenously in asci

3. Q3 · 2 marks · Very short answerExam level

   What are viroids? Who discovered them? (2 marks)

   Hint

   Naked RNA.

   Answer

   Viroids are infectious agents of free, low-molecular-weight RNA without a protein coat (1); discovered by T.O. Diener in 1971 as the cause of potato spindle tuber disease (1).

4. Q4 · 2 marks · Very short answerHarder exam level

   Why are dinoflagellates described as having two flagella in different positions? Describe their wall. (2 marks)

   Hint

   Longitudinal and transverse.

   Answer

   One flagellum lies longitudinally and the other transversely in a furrow between wall plates (1). The wall has stiff cellulose plates on the outer surface (1).

5. Q5 · 2 marks · Very short answerHarder exam level

   Distinguish between chemosynthetic and photosynthetic autotrophic bacteria with one example of each group's role. (2 marks)

   Hint

   Energy source.

   Answer

   Photosynthetic (cyanobacteria) use light energy and chlorophyll a; e.g. Nostoc fixes nitrogen (1). Chemosynthetic bacteria get energy by oxidising inorganic substances (nitrites, ammonia), helping recycle N, P, Fe and S (1).

6. Q6 · 2 marks · Very short answerHarder exam level

   Suppose you find a fungus that reproduces only by conidia and has septate mycelium. Into which class would you place it, and what would happen if a sexual stage were later found? (2 marks)

   Hint

   Fungi imperfecti.

   Answer

   Deuteromycetes (1). If a sexual stage is discovered, it is moved to ascomycetes or basidiomycetes depending on its sexual spores (1).

7. Q7 · 3 marks · Short answerHarder exam level

   Explain the role of the alga and the fungus in a lichen. Why do lichens grow on bare rocks where few plants can? (3 marks)

   Hint

   Food and shelter.

   Answer

   Alga (phycobiont) makes food by photosynthesis (1). Fungus (mycobiont) gives shelter and absorbs water and minerals (1). Together they survive harsh, nutrient-poor surfaces that neither could colonise alone (1).

8. Q8 · 3 marks · Short answerHarder exam level

   Compare plasmogamy and karyogamy, and explain the dikaryophase. In which classes is it seen? (3 marks)

   Hint

   Cytoplasm vs nuclei.

   Answer

   Plasmogamy: fusion of protoplasms of two cells (1). Karyogamy: fusion of their nuclei (1). In ascomycetes and basidiomycetes, a dikaryotic (n + n) stage with two unfused nuclei per cell occurs between the two steps (1).

9. Q9 · 2 marks · Very short answerHarder exam level

   Name the disease and causative organism: (a) sleeping sickness (b) wheat rust (c) mad cow disease (d) white rust of mustard. (2 marks)

   Hint

   Protozoa, fungi and prions.

   Answer

   (a) Trypanosoma (b) Puccinia (c) prion (d) Albugo (½ each).

10. Q10 · 3 marks · Short answerHOTS / competency

    Suppose an aquarium owner sees the water turn green and fish dying after he overfeeds them. Explain using the features of cyanobacteria, and suggest one remedy. (3 marks)

    Hint

    Blooms in polluted water.

    Answer

    Excess food adds nutrients (organic matter, nitrates, phosphates) (1). Cyanobacteria multiply rapidly and form a bloom, covering the surface; at night and when they die, oxygen falls, killing fish (1). Remedy: reduce feeding, change water or aerate (1).

11. Q11 · 5 marks · Long answerHOTS / competency

    (a) Explain why the five-kingdom classification is still not perfect. (b) Discuss where viruses, viroids, prions and lichens would fit or not fit in it. (c) How does the three-domain system address one weakness? (5 marks)

    Hint

    Acellular agents and archaebacteria.

    Answer

    (a) Protista has poorly defined boundaries; some organisms show features of two kingdoms (1). (b) Viruses, viroids and prions are acellular, so they fit no kingdom (1); lichens are associations of two organisms from different kingdoms, so they are not a single kingdom member (1). (c) Archaebacteria differ fundamentally from eubacteria; the three-domain system separates them as Archaea, Bacteria and Eukarya (2).

12. Q12 · 1 mark · Assertion-reasonHOTS / competency

    Assertion (A): Lichens are good pollution indicators.
    Reason (R): Lichens do not grow in polluted areas.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

    Hint

    Sensitivity to SO₂.

    Answer

    (a)

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Who proposed the five-kingdom classification?Show answer

   R.H. Whittaker (1969).

2. 2.What are heterocysts?Show answer

   Specialised cells of some cyanobacteria (Nostoc, Anabaena) that fix atmospheric nitrogen.

3. 3.Name the smallest living cells known.Show answer

   Mycoplasma.

4. 4.What is diatomaceous earth used for?Show answer

   Polishing, and filtration of oils and syrups.

5. 5.Which protist causes red tides?Show answer

   Red dinoflagellates such as Gonyaulax.

6. 6.What is a pellicle?Show answer

   A protein-rich layer in euglenoids that replaces the cell wall and keeps the body flexible.

7. 7.Name the fungus used in genetic and biochemical work.Show answer

   Neurospora.

8. 8.Why are deuteromycetes called fungi imperfecti?Show answer

   Only their asexual or vegetative phases are known.

9. 9.Who showed that viruses can be crystallised?Show answer

   W.M. Stanley (1935).

10. 10.What are phycobiont and mycobiont?Show answer

    The algal and fungal partners of a lichen.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you list three drawbacks of the two-kingdom system?
• ☐Can you name the three archaebacteria groups with habitats?
• ☐Can you explain heterocysts and blooms?
• ☐Can you describe diatoms, dinoflagellates and euglenoids in two lines each?
• ☐Can you name the four protozoan groups with examples?
• ☐Can you compare the four fungal classes in a table?
• ☐Can you explain plasmogamy, karyogamy and dikaryophase?
• ☐Can you distinguish virus, viroid and prion and describe lichens?

Biological Classification: frequently asked questions