How to Use This Section
Biological Classification is a memory chapter with a logic underneath it. The logic is Table 2.1 - cell type, cell wall, nuclear membrane, body organisation, mode of nutrition - and almost every "identify the kingdom" question in NEET is that table read as a decision tree. The memory is the named examples, and there are close to fifty of them.
These 36 questions are organised in three tiers:
- Concept Checks - direct recall of definitions, characters and named examples.
- Application and Scenarios - you are handed an unnamed organism or a set of characters and asked to place it, or you are asked to compare two groups.
- Analytical and Multi-Concept - reasoning that crosses kingdoms, plus the open-ended discussion questions.
Coverage of the chapter-end exercises
| Exercise | Where it is answered |
|---|---|
| 1 - How classification systems have undergone several changes over time | Question 29 |
| 2 - Two economically important uses of heterotrophic bacteria and of archaebacteria | Question 17 |
| 3 - The nature of cell-walls in diatoms | Question 10 |
| 4 - What the terms algal bloom and red-tides signify | Question 18 |
| 5 - How viroids are different from viruses | Question 19 |
| 6 - The four major groups of Protozoa | Question 20 |
| 7 - Plants that are partially heterotrophic | Question 21 |
| 8 - What the terms phycobiont and mycobiont signify | Question 15 |
| 9 - A comparative account of the classes of Kingdom Fungi | Question 22 |
| 10 - The characteristic features of Euglenoids | Question 23 |
| 11 - Viruses - structure, nature of genetic material, and four viral diseases | Question 24 |
| 12 - Are viruses living or non-living | Question 30 |
Every chapter-end exercise is worked here, so this section is the one place to check that you have covered the textbook in full.
The Facts These Examples Draw On
Table 2.1 in one line each: Monera - prokaryotic, noncellulosic wall, no nuclear membrane, cellular, autotrophic and heterotrophic. Protista - eukaryotic, wall in some, cellular, autotrophic and heterotrophic. Fungi - eukaryotic, chitin wall, multicellular or loose tissue, heterotrophic. Plantae - eukaryotic, cellulose wall, tissue or organ, autotrophic. Animalia - eukaryotic, no wall, tissue / organ / organ system, heterotrophic holozoic.
The names, by group.
- Monera: Nostoc, Anabaena (heterocysts, N-fixation); Mycoplasma (no wall, smallest cells); halophiles, thermoacidophiles, methanogens.
- Protista: diatoms and desmids (chrysophytes); Gonyaulax (dinoflagellate, red tide); Euglena (euglenoid, pellicle); slime moulds (plasmodium); Amoeba, Entamoeba, Trypanosoma, Paramoecium, Plasmodium.
- Fungi: Mucor, Rhizopus, Albugo (Phycomycetes); Aspergillus, Claviceps, Neurospora, yeast, morels, truffles (Ascomycetes); Agaricus, Ustilago, Puccinia (Basidiomycetes); Alternaria, Colletotrichum, Trichoderma (Deuteromycetes); Penicillium (antibiotics).
- Plantae: bladderwort, Venus fly trap, Cuscuta.
- Acellular: viruses (Ivanowsky 1892, Beijerinck 1898, Stanley 1935); viroids (Diener 1971); prions (BSE, CJD); lichens (phycobiont, mycobiont).
Tier 1 - Concept Checks
Question 1
Q. Name the five kingdoms of Whittaker and the year of proposal.
Answer. Monera, Protista, Fungi, Plantae, Animalia; 1969.
Question 2
Q. State Whittaker's five criteria for classification.
Answer. Cell structure, body organisation, mode of nutrition, reproduction and phylogenetic relationships.
Question 3
Q. Which kingdom is prokaryotic and which kingdom lacks a cell wall?
Answer. Prokaryotic: Monera. No cell wall: Animalia.
Question 4
Q. Give the cell wall composition in Monera, Fungi and Plantae.
Answer. Monera: noncellulosic - polysaccharide + amino acid. Fungi: chitin. Plantae: cellulose.
Question 5
Q. Name the four bacterial shape categories with their shapes.
Answer. Coccus - spherical; bacillus - rod-shaped; vibrium - comma-shaped; spirillum - spiral.
Question 6
Q. Match the archaebacterium to its habitat: Halophiles, thermoacidophiles, methanogens.
Answer. Halophiles - extreme salty areas. Thermoacidophiles - hot springs. Methanogens - marshy areas.
Question 7
Q. In which cells do cyanobacteria fix nitrogen, and name two examples.
Answer. In heterocysts; Nostoc and Anabaena.
Question 8
Q. State four facts about Mycoplasma.
Answer. They completely lack a cell wall; they are the smallest living cells known; they can survive without oxygen; many are pathogenic in animals and plants.
Question 9
Q. Which five groups are included under Protista in this book?
Answer. Chrysophytes, dinoflagellates, euglenoids, slime moulds and protozoans.
Question 10
Q. What is the nature of cell-walls in diatoms?
Answer. They form two thin overlapping shells which fit together as in a soap box, and are embedded with silica, making them indestructible.
Takeaway: This is one of the chapter-end exercises.
Question 11
Q. Name the four groups of protozoans with one example each.
Answer. Amoeboid - Amoeba (and the parasite Entamoeba); flagellated - Trypanosoma; ciliated - Paramoecium; sporozoans - Plasmodium.
Question 12
Q. Name the three steps of the fungal sexual cycle.
Answer. (i) Plasmogamy - fusion of protoplasms; (ii) karyogamy - fusion of two nuclei; (iii) meiosis in the zygote giving haploid spores.
Question 13
Q. List the asexual and sexual spores of fungi.
Answer. Asexual: conidia, sporangiospores, zoospores. Sexual: oospores, ascospores, basidiospores.
Question 14
Q. Give the four fungal classes with their example genera.
Answer. Phycomycetes - Mucor, Rhizopus, Albugo. Ascomycetes - Aspergillus, Claviceps, Neurospora. Basidiomycetes - Agaricus, Ustilago, Puccinia. Deuteromycetes - Alternaria, Colletotrichum, Trichoderma.
Question 15
Q. What do the terms phycobiont and mycobiont signify?
Answer. The two partners of a lichen - a symbiotic, mutually useful association between algae and fungi. The phycobiont is the algal component and is autotrophic; the mycobiont is the fungal component and is heterotrophic. Algae prepare food for the fungi; fungi provide shelter and absorb mineral nutrients and water.
Takeaway: This is one of the chapter-end exercises.
Question 16
Q. Name the discoverer, year and disease associated with viroids.
Answer. T. O. Diener, 1971, potato spindle tuber disease.
Tier 2 - Application and Scenarios
Question 17
Q. State two economically important uses of (a) heterotrophic bacteria and (b) archaebacteria.
Answer. (a) Heterotrophic bacteria: making curd from milk; production of antibiotics. (Also: fixing nitrogen in legume roots, and their role as important decomposers.) (b) Archaebacteria: methanogens in the gut of ruminants such as cows and buffaloes produce methane, that is biogas, from dung, which is used as fuel; the same organisms are used in biogas plants for treating animal waste.
Takeaway: This is one of the chapter-end exercises.
Question 18
Q. Find out what the terms 'algal bloom' and 'red-tides' signify.
Answer.
- Algal bloom: an excessive growth of algae in a water body. cyanobacteria often form blooms in polluted water bodies, so a bloom signals nutrient-rich, typically polluted water.
- Red tide: the reddening of the sea when red dinoflagellates such as Gonyaulax undergo such rapid multiplication that they make the sea appear red. Toxins released by such large numbers may even kill other marine animals such as fishes.
Takeaway: Name the causative organism in each - cyanobacteria for the bloom, Gonyaulax for the red tide. This is one of the chapter-end exercises.
Question 19
Q. How are viroids different from viruses?
Answer. A viroid is smaller than a virus; it is a free RNA and lacks the protein coat (capsid) found in viruses; its RNA is of low molecular weight; and while a virus may carry either RNA or DNA, a viroid is always RNA.
Takeaway: This is one of the chapter-end exercises.
Question 20
Q. Describe briefly the four major groups of Protozoa.
Answer.
- Amoeboid protozoans - fresh water, sea water or moist soil; move and capture prey by pseudopodia (false feet); marine forms have silica shells; Amoeba, and Entamoeba as a parasite.
- Flagellated protozoans - free-living or parasitic; have flagella; parasitic forms cause sleeping sickness; Trypanosoma.
- Ciliated protozoans - aquatic, actively moving with thousands of cilia; a gullet opens to the cell surface and coordinated movement of rows of cilia steers food-laden water into it; Paramoecium.
- Sporozoans - have an infectious spore-like stage in the life cycle; Plasmodium, the malarial parasite.
Takeaway: This is one of the chapter-end exercises.
Question 21
Q. Plants are autotrophic. Can you think of some plants that are partially heterotrophic?
Answer. Yes - insectivorous plants such as the bladderwort and the Venus fly trap, and parasites such as Cuscuta. They are only partially heterotrophic because they retain chlorophyll and still photosynthesise.
Takeaway: This is one of the chapter-end exercises.
Question 22
Q. Give a comparative account of the classes of Kingdom Fungi under (i) mode of nutrition and (ii) mode of reproduction.
Answer.
(i) Mode of nutrition
- Phycomycetes: aquatic, or on decaying wood in moist and damp places, or obligate parasites on plants.
- Ascomycetes: saprophytic, decomposers, parasitic or coprophilous (growing on dung).
- Basidiomycetes: in soil, on logs and tree stumps, and parasitic in living plant bodies as rusts and smuts.
- Deuteromycetes: saprophytes or parasites; a large number are decomposers of litter helping in mineral cycling.
(ii) Mode of reproduction
- Phycomycetes: asexual by zoospores (motile) or aplanospores (non-motile), produced endogenously in a sporangium; sexual by fusion of isogamous, anisogamous or oogamous gametes forming a zygospore.
- Ascomycetes: asexual by conidia produced exogenously on conidiophores; sexual by ascospores produced endogenously in asci, borne in ascocarps.
- Basidiomycetes: asexual spores generally not found; fragmentation common; sex organs absent, plasmogamy by fusion of two somatic cells of different strains, giving a dikaryotic structure and then the basidium, where karyogamy and meiosis produce four exogenous basidiospores borne in basidiocarps.
- Deuteromycetes: only asexually, by conidia; the sexual stage is unknown.
Takeaway: Answer as a four-by-two grid. This is one of the chapter-end exercises.
Question 23
Q. What are the characteristic features of Euglenoids?
Answer. Majority are fresh water organisms found in stagnant water; instead of a cell wall they have a protein rich layer called pellicle which makes the body flexible; they have two flagella, a short and a long one; they are photosynthetic in sunlight but behave like heterotrophs, predating on smaller organisms, when deprived of sunlight; their pigments are identical to those present in higher plants. Example: Euglena.
Takeaway: This is one of the chapter-end exercises.
Question 24
Q. Give a brief account of viruses with respect to their structure and nature of genetic material, and name four common viral diseases.
Answer. Structure: a virus is non-cellular and is a nucleoprotein, inert and crystalline outside the living cell and an obligate parasite. The nucleic acid is protected by a capsid, a protein coat made of capsomeres arranged in helical or polyhedral geometric forms. Once it infects a cell it takes over the host machinery to replicate, killing the host. Genetic material: either RNA or DNA - never both, and it is infectious. Plant viruses generally have single stranded RNA; animal viruses have single or double stranded RNA or double stranded DNA; bacteriophages are usually double stranded DNA viruses. Four diseases: mumps, small pox, herpes, influenza (and AIDS).
Takeaway: This is one of the chapter-end exercises.
Question 25
Q. An organism is eukaryotic, unicellular, has no cell wall, is aquatic, and moves using thousands of short hair-like projections. Identify kingdom, group and a likely genus.
Answer. Kingdom Protista (single-celled eukaryote), ciliated protozoan (thousands of cilia, actively moving, aquatic), likely genus Paramoecium.
Question 26
Q. A filamentous organism has septate hyphae, produces conidia exogenously, and forms sac-like structures containing spores. Name the class and two examples.
Answer. Ascomycetes. The branched septate mycelium, conidia produced exogenously on conidiophores and ascospores produced endogenously in sac-like asci are all diagnostic. Examples: Aspergillus, Claviceps or Neurospora.
Question 27
Q. Classify the following into their kingdoms: Nostoc, Paramoecium, Agaricus, Cuscuta, Mycoplasma.
Answer.
- Nostoc - Monera (a cyanobacterium, prokaryotic).
- Paramoecium - Protista (a ciliated protozoan, single-celled eukaryote).
- Agaricus - Fungi (a basidiomycete mushroom).
- Cuscuta - Plantae (a partially heterotrophic parasitic plant).
- Mycoplasma - Monera (a wall-less bacterium, the smallest living cell).
Question 28
Q. Match each organism with the disease it causes: Trypanosoma, Plasmodium, Puccinia, Albugo.
Answer. Trypanosoma - sleeping sickness. Plasmodium - malaria. Puccinia - wheat rust. Albugo - the white spots on mustard leaves (a parasitic fungus of mustard).
Tier 3 - Analytical and Multi-Concept
Question 29
Q. Discuss how classification systems have undergone several changes over a period of time.
Answer.
- Earliest attempts were instinctive, borne out of a need to use organisms for food, shelter and clothing.
- Aristotle gave the first more scientific basis using simple morphological characters - plants into trees, shrubs and herbs, animals by presence or absence of red blood.
- In Linnaeus' time the Two Kingdom system of Plantae and Animalia was developed. It could not distinguish eukaryotes from prokaryotes, unicellular from multicellular, or photosynthetic from non-photosynthetic organisms, and a large number of organisms did not fall into either category.
- Gross morphology on its own was not enough, so cell structure, nature of wall, mode of nutrition, habitat, methods of reproduction and evolutionary relationships had to be brought in as well.
- R. H. Whittaker (1969) proposed the Five Kingdom Classification on five criteria - fungi separated on chitin walls and heterotrophy, all prokaryotes placed in Monera, unicellular eukaryotes in Protista.
- Later the three-domain system split Monera into two domains, giving a six kingdom classification.
- Throughout, plant and animal kingdoms remained constant in name but what was included in them kept changing, and such changes will take place in future too as understanding of characteristics and evolutionary relationships improves.
Takeaway: A 5-mark answer, and the numbered sequence is where the marks are. This is one of the chapter-end exercises.
Question 30
Q. Organise the arguments on the topic: Are viruses living or non-living?
Answer. Non-living: they are non-cellular, and living is understood here as having cell structure; outside the host they have an inert crystalline structure - Stanley (1935) crystallised them and found the crystals largely protein; they are inert outside their specific host cell and are obligate parasites with no independent metabolism. Living: they contain genetic material (RNA or DNA) which is infectious; they replicate, albeit by taking over the host cell machinery; Beijerinck named the agent Contagium vivum fluidum - infectious living fluid. The resolution: the question is a boundary problem. Viruses fall outside the five kingdom scheme because the scheme is built on cell structure, which viruses lack.
Takeaway: This is one of the chapter-end exercises.
Question 31
Q. Chlamydomonas, Chlorella, Paramoecium and Amoeba were once in two different kingdoms and are now in one. Explain, and state the general principle.
Answer. Chlamydomonas and Chlorella were placed in Algae within Plants because they have cell walls; Paramoecium and Amoeba were placed in the animal kingdom because they lack cell walls. All four are now in Kingdom Protista because they are single-celled eukaryotes.
The general principle: the organisms did not change - the criteria for classification changed, from presence of a cell wall to cell structure and cellularity. such changes will take place in future too, depending on improvements in our understanding of characteristics and evolutionary relationships.
Question 32
Q. Cyanobacteria are photosynthetic and are called blue-green algae, yet they are not in Plantae. Diatoms are photosynthetic and are the chief producers of the oceans, yet they are not in Plantae either. Explain both placements.
Answer.
- Cyanobacteria to Monera: they are prokaryotic - no nuclear membrane, no membrane-bound organelles. Whittaker's criterion of cell structure places all prokaryotic organisms in Monera, regardless of nutrition. Their chlorophyll a, similar to green plants, and their photosynthetic autotrophy do not override this.
- Diatoms to Protista: they are eukaryotic but single-celled, and all single-celled eukaryotes are placed under Protista. Being photosynthetic and the chief producers in the oceans is a matter of mode of nutrition, which is only one of five criteria.
- Plantae requires eukaryotic chlorophyll-containing organisms with tissue or organ level body organisation and a cellulose wall - a level of organisation neither group reaches.
Takeaway: Nutrition alone never decides a kingdom. Read cell type and body organisation first.
Question 33
Q. Both slime moulds and fungi are saprophytic and both form spore-bearing fruiting bodies. Why are they in different kingdoms?
Answer. Because body organisation and cell structure decide, not habit. Slime moulds are protists - their body is cellular, moving as a mass along decaying twigs and leaves and forming a plasmodium under suitable conditions. Fungi are filamentous, built of hyphae forming a mycelium, with cell walls of chitin and polysaccharides and a body organisation described as multicellular or loose tissue.
The shared saprophytic nutrition and the shared spore-bearing fruiting bodies are convergent similarities in habit, and habit is only one of Whittaker's five criteria.
Question 34
Q. Arrange these four in order of increasing structural complexity and justify: a prion, a virus, Mycoplasma, Paramoecium.
Answer. Prion to virus to Mycoplasma to Paramoecium.
- Prion: abnormally folded protein only - no nucleic acid, no cell.
- Virus: a nucleoprotein - RNA or DNA inside a capsid of capsomeres - but still non-cellular and inert outside the host.
- Mycoplasma: a cell - in fact the smallest living cell known - though completely lacking a cell wall; prokaryotic, in Kingdom Monera.
- Paramoecium: a eukaryotic cell with a well defined nucleus and membrane-bound organelles, thousands of cilia and a gullet; Kingdom Protista.
Takeaway: The jump that matters is between virus and Mycoplasma - that is the line between non-cellular and cellular, and it is the line the five kingdom classification is built on.
Question 35
Q. A wall-less, chlorophyll-bearing, single-celled organism switches to predation in the dark. Two biologists disagree about its kingdom. Explain the disagreement and settle it.
Answer. The organism is a euglenoid, such as Euglena.
- The botanist's case: it is photosynthetic in sunlight and its pigments are identical to those present in higher plants.
- The zoologist's case: it has no cell wall, only a flexible protein-rich pellicle; it is motile with two flagella; and it behaves like a heterotroph, predating on smaller organisms, when deprived of sunlight.
The settlement: the chapter expects this exact disagreement, because the boundaries of Protista are not well defined, so what may be 'a photosynthetic protistan' to one biologist may be 'a plant' to another. Whittaker's system resolves it on cell structure and body organisation: a single-celled eukaryote is a protist, whatever its nutrition. So the organism is in Kingdom Protista.
Question 36
Q. Take the four class-defining features of Basidiomycetes - septate mycelium, no asexual spores, absent sex organs, four exogenous basidiospores - and explain how each one separates it from a different fungal class.
Answer.
- Septate mycelium separates it from Phycomycetes, whose mycelium is aseptate and coenocytic.
- Asexual spores generally not found separates it from Deuteromycetes, which reproduce only by asexual conidia, and from Ascomycetes, whose conidia are abundant.
- Sex organs absent, plasmogamy by fusion of two somatic cells of different strains separates it from Phycomycetes, where gametes - isogamous, anisogamous or oogamous - fuse to form a zygospore.
- Four basidiospores produced exogenously on the basidium separates it from Ascomycetes, whose ascospores are produced endogenously in asci.
Takeaway: Every class boundary in Kingdom Fungi comes back to the three criteria - mycelium morphology, mode of spore formation, fruiting bodies. If you can say which of the three a given difference belongs to, you can reconstruct the whole comparison table.