Previous year questions: Biological Classification

Previous year questions: biological classification

All ten items are from the official NCERT Exemplar Problems in Biology for Class 11. The exemplar does not print marks against individual questions, so the marks shown here follow the section the question is printed in: one mark for a multiple choice item, two marks for a very short answer, three marks for a short answer and five marks for a long answer. Each heading names the exemplar chapter and the question number inside its section. Work each answer before you read the model answer, because the exemplar repeats its vocabulary across items.

Q1 (NCERT Exemplar, 1 mark)

NCERT Exemplar Class 11 Biology, Chapter 2, Multiple Choice Questions, Q2. The five kingdom classification was proposed by which of these scientists?

Answer: The correct name is R.H. Whittaker, who proposed the five kingdom system in 1969. Linnaeus gave the two kingdom system and the binomial naming system. The other names printed in the options are not associated with the five kingdom arrangement. Whittaker placed all prokaryotes in Monera and all single-celled eukaryotes in Protista, and that division is the heart of his proposal.

Q2 (NCERT Exemplar, 1 mark)

NCERT Exemplar Class 11 Biology, Chapter 2, Multiple Choice Questions, Q8. Associations between a mycobiont and a phycobiont are found in which of these?

Answer: The association of a mycobiont with a phycobiont is found in lichens. The mycobiont is the fungal partner and the phycobiont is the algal partner. Mycorrhiza is a different association, between a fungus and the roots of a higher plant, and it does not involve a phycobiont.

Q3 (NCERT Exemplar, 2 marks)

NCERT Exemplar Class 11 Biology, Chapter 2, Very Short Answer Type Questions, Q2. An old slide without a label shows a unicellular organism with a well-defined nucleus and two flagella, one lying lengthwise and one crosswise in a groove. Identify it and name its kingdom.

Answer: The organism is a dinoflagellate. It is unicellular, eukaryotic, and has the two flagella arranged in the characteristic dinoflagellate way, with one longitudinal and the other transverse in a groove between the cellulose wall plates. The two flagella are the giveaway, and the cellulose plates of the wall are visible when the slide is focused carefully. Dinoflagellates are placed in Kingdom Protista. Gonyaulax is the standard example.

Q4 (NCERT Exemplar, 2 marks)

NCERT Exemplar Class 11 Biology, Chapter 2, Very Short Answer Type Questions, Q3. How is the five kingdom classification advantageous over the two kingdom classification?

Answer: It separates prokaryotes from eukaryotes, so bacteria are no longer mixed with plants and animals. It separates single-celled eukaryotes into Protista and keeps the many-celled organisms in their own kingdoms. It gives fungi a separate kingdom on the strength of the chitin wall and heterotrophic absorption, which the two kingdom system could not do. It also brings nutrition and descent into the criteria, instead of relying on gross form alone. The two kingdom system had no place for organisms that are neither clearly plant nor clearly animal, and the five kingdom system gives them a home in Protista or in Fungi.

Q5 (NCERT Exemplar, 2 marks)

NCERT Exemplar Class 11 Biology, Chapter 2, Very Short Answer Type Questions, Q7. A virus is treated as living inside a host cell, yet it is not classified with bacteria or fungi. Which characters of a virus are similar to non-living objects?

Answer: Outside a host, a virus behaves as an inert chemical. Its particle has no cells, no cytoplasm and no metabolic reactions of its own. Stanley showed that viruses can be crystallised, and crystals are a property of chemical substances rather than of living bodies. A virus cannot grow on its own or reproduce without a host cell. These are the characters that make it look non-living and keep it outside the cell-based kingdoms. The crystallisation is the strongest evidence, because crystals are formed by chemical substances, and the chapter calls the virus inert outside its specific host.

Q6 (NCERT Exemplar, 3 marks)

NCERT Exemplar Class 11 Biology, Chapter 2, Short Answer Type Questions, Q1. Diatoms are called the pearls of the ocean. Why? What is diatomaceous earth?

Answer: Diatoms are microscopic photosynthetic protists that drift in the water as plankton, and they are the chief producers of the oceans. The name pearls of the ocean comes from their shells, because the silica wall is built of two fitted halves and its fine ornamentation gives it the look of a glass box. The role of chief producer is a separate point about their place in the food chain. When diatoms die, their hard walls settle on the bottom. The deposit that collects over billions of years is diatomaceous earth. It is gritty and porous, and it is used for polishing and for filtering oils and syrups.

Q7 (NCERT Exemplar, 3 marks)

NCERT Exemplar Class 11 Biology, Chapter 2, Short Answer Type Questions, Q4. Cyanobacteria and heterotrophic bacteria have been placed together in the eubacteria of Kingdom Monera, though the two differ widely. Is the grouping justified? Give reasons.

Answer: The grouping is justified at the level of the kingdom because both kinds are prokaryotic. Neither has a membrane-bound nucleus or membrane-bound organelles, both have a rigid cell wall, and both show the bacterial type of cell organisation. The difference between them sits in nutrition, with cyanobacteria photosynthesising their own food and heterotrophic bacteria depending on organic matter. In classification, cell structure is a more fundamental criterion than the mode of nutrition, so the two stay together in one kingdom. Cell organisation decides where an organism sits in the largest division of the living world, while nutrition can vary within one group.

Q8 (NCERT Exemplar, 3 marks)

NCERT Exemplar Class 11 Biology, Chapter 2, Short Answer Type Questions, Q6. What observable features of Trypanosoma would make you place it in Kingdom Protista?

Answer: Trypanosoma is a single-celled eukaryotic organism. Its cell has a well-defined nucleus and membrane-bound organelles, which rules out Monera. It carries flagella and moves actively, and it lives as a parasite in the blood of vertebrates, causing sleeping sickness. It is heterotrophic and has no cell wall. A single-celled eukaryote that is not a fungus belongs in Protista, and that is where Trypanosoma is placed.

Q9 (NCERT Exemplar, 3 marks)

NCERT Exemplar Class 11 Biology, Chapter 2, Short Answer Type Questions, Q7. Fungi are cosmopolitan. Write the role of fungi in daily life.

Answer: Fungi are useful in food and drink: yeasts raise bread and ferment beer, and mushrooms and truffles are eaten. Penicillium is the source of the antibiotic penicillin, and other fungi give useful chemicals. Fungi decompose dead plant and animal matter and return minerals to the soil, which keeps nutrient cycles running. Some fungi form mycorrhiza with plant roots and help the plant take up minerals. Against these uses, fungi also spoil food, and some cause disease in plants, animals and people, so fungi touch daily life on both sides.

Q10 (NCERT Exemplar, 5 marks)

NCERT Exemplar Class 11 Biology, Chapter 2, Long Answer Type Questions, Q5. Biological classification is dynamic and keeps changing with our understanding of life forms. Justify the statement with two examples.

Answer: Classification is a model of relationships, so it changes when the evidence changes. The first example is the move from two kingdoms to five. Linnaeus placed every organism in Plantae or Animalia, which put bacteria and blue-green algae with plants and left many organisms outside both kingdoms. Whittaker's five kingdoms separated prokaryotes, single-celled eukaryotes, fungi, plants and animals, because cell structure, wall chemistry and nutrition became part of the criteria. The second example is the place of fungi. Fungi were once treated as plants that lacked chlorophyll, but the chitin wall, the absorptive nutrition and the different body plan moved them to their own kingdom. A third example comes from Protista itself: Chlamydomonas and Amoeba, once placed in different kingdoms, now sit together because both are single-celled eukaryotes. A fourth change is the place of cyanobacteria. They were once called blue-green algae and grouped with plants, but they are prokaryotic, so they now sit with the bacteria in Monera. Each change came from better understanding, not from a fault in the earlier workers.