Previous year questions: Plant Kingdom

Previous year questions: plant kingdom

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 reading the model answer, because the exemplar repeats its vocabulary across items. Most items can be answered by naming the group, one printed example and one defining character.

Q1 (NCERT Exemplar, 1 mark)

NCERT Exemplar Class 11 Biology, Chapter 3, Multiple Choice Questions, Q2. The fusion of two motile gametes that are dissimilar in size is called which of these?

Answer: The correct term is anisogamy. In anisogamy the two gametes are both motile but differ in size, so the pair sits between isogamy and oogamy. Isogamy fuses gametes of the same size, oogamy fuses a large non-motile female gamete with a small motile male gamete, and zoogamy is not one of the terms used for this classification.

Q2 (NCERT Exemplar, 1 mark)

NCERT Exemplar Class 11 Biology, Chapter 3, Multiple Choice Questions, Q3. A plant body made of a holdfast, a stipe and a frond belongs to which class of algae?

Answer: The class is Phaeophyceae, the brown algae. Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus show this body plan: a holdfast that fixes the plant to a surface, a stalk or stipe, and a leaf-like photosynthetic frond. The other two algal classes do not build this three-part body, and this is a definition item where the exact term earns the mark. The chapter treats the holdfast, the stipe and the frond together as the brown algal body plan, and that combination is what separates the class in a question.

Q3 (NCERT Exemplar, 1 mark)

NCERT Exemplar Class 11 Biology, Chapter 3, Multiple Choice Questions, Q4. A plant has a thallus body, rhizoids, a haploid plant body and motile male gametes that need water. Which group does it belong to?

Answer: The group is the bryophytes. A thalloid haploid body with rhizoids and a dependence on water for the motile male gametes is exactly the bryophyte description. Pteridophytes and gymnosperms have a dominant sporophyte, and monocots are flowering plants with a well-developed vascular body.

Q4 (NCERT Exemplar, 2 marks)

NCERT Exemplar Class 11 Biology, Chapter 3, Very Short Answer Type Questions, Q3. The higher plants have roots for absorption. What is the equivalent of roots in the less developed lower plants?

Answer: In the lower plants the equivalent is the rhizoid. Bryophytes attach to the ground with unicellular or multicellular rhizoids, and these hold the thallus in place and take up water and salts from the damp surface. Rhizoids are not true roots: they have no vascular tissue, and they cannot absorb from deep soil the way a root system does.

Q5 (NCERT Exemplar, 2 marks)

NCERT Exemplar Class 11 Biology, Chapter 3, Very Short Answer Type Questions, Q5. What are the male and female sex organs of a bryophyte called?

Answer: The male sex organ is the antheridium, and it produces biflagellate antherozoids. The female sex organ is the archegonium, which is flask-shaped and holds one egg. After water carries an antherozoid to the archegonium, the egg is fertilised inside it and the zygote grows into the sporophyte. Both organs are many-celled, and both are borne on the haploid plant body.

Q6 (NCERT Exemplar, 3 marks)

NCERT Exemplar Class 11 Biology, Chapter 3, Short Answer Type Questions, Q1. Why are bryophytes called the amphibians of the plant kingdom?

Answer: The name has two halves. Bryophytes are land plants: they grow on soil, on rocks and on bark, and their body is exposed to air. Yet they need water for sexual reproduction, because the biflagellate antherozoids must swim through a water film to reach the archegonium. Their body is thalloid with rhizoids rather than true roots, stems and leaves, so they cannot live in dry places. A plant that lives on land but needs water to complete its sexual cycle is fairly called an amphibian of the plant kingdom. Neither half alone would earn the name.

Q7 (NCERT Exemplar, 3 marks)

NCERT Exemplar Class 11 Biology, Chapter 3, Short Answer Type Questions, Q3. Heterospory is the formation of microspores and megaspores. Does it carry evolutionary significance in the plant kingdom?

Answer: It does, and the significance lies in what heterospory makes possible. The megaspore grows into a female gametophyte and the microspore into a male gametophyte, so the two sexes get separate homes. In heterosporous pteridophytes the female gametophyte is retained on the parent sporophyte, and the young embryo develops inside it. Retention of the embryo on the parent plant is the essential step towards the seed habit, and it is the reason heterospory is treated as an evolutionary advance rather than a small variation. Selaginella and Salvinia are the pteridophyte examples to quote.

Q8 (NCERT Exemplar, 3 marks)

NCERT Exemplar Class 11 Biology, Chapter 3, Short Answer Type Questions, Q6. How are heterosporous pteridophytes a precursor to the seed habit of gymnosperms?

Answer: In heterosporous pteridophytes such as Selaginella, two kinds of spores are produced. The megaspore germinates into a female gametophyte that stays attached to the parent sporophyte instead of being free-living. Fertilisation happens while this gametophyte is still on the parent, and the embryo develops inside it. A seed is built on the same plan: a retained female gametophyte, a fertilised egg and an embryo enclosed with food. The pteridophyte arrangement lacks the seed coat and the full enclosure, which is why it is called a precursor rather than a seed. The megaspore is the large spore that keeps food for the young gametophyte, while the microspore is the small spore that gives rise to the male gametophyte.

Q9 (NCERT Exemplar, 3 marks)

NCERT Exemplar Class 11 Biology, Chapter 3, Short Answer Type Questions, Q8. How are the male and female gametophytes of pteridophytes different from those of gymnosperms?

Answer: In pteridophytes the gametophyte is a separate free-living plant. The spore grows into a small green photosynthetic prothallus that lives on damp soil and bears antheridia and archegonia on its own. In gymnosperms the gametophytes are reduced and not free-living. The male gametophyte is the pollen grain, only a few cells inside a wall, and the female gametophyte stays inside the megasporangium on the parent sporophyte. The pteridophyte gametophyte needs water for fertilisation, while the gymnosperm pollen tube carries the male gametes to the archegonia. That difference in delivery is the clearest sign that the gymnosperm gametophytes no longer live on their own.

Q10 (NCERT Exemplar, 5 marks)

NCERT Exemplar Class 11 Biology, Chapter 3, Long Answer Type Questions, Q1. The gametophyte is the dominant phase in a bryophyte. Explain.

Answer: The plant body that a person sees in a bryophyte is the gametophyte, and it is haploid. In a moss it begins as the protonema, a green branched filament that grows from a spore, and then produces the leafy stage with upright axes and spirally arranged leaves. This leafy gametophyte carries the sex organs at the tip of its shoots: antheridia that make biflagellate antherozoids, and flask-shaped archegonia that hold an egg each. Water carries the antherozoids to the archegonia, and fertilisation produces a zygote. A wet surface is therefore not a small detail but the condition for the whole sexual cycle. The zygote grows into the sporophyte, which has a foot, a seta and a capsule. The sporophyte never becomes independent: it stays attached to the gametophyte and takes its food from it. Some cells of the capsule then undergo meiosis and make haploid spores, and the spores grow into new gametophytes. The gametophyte is therefore the plant that grows, feeds itself, makes the gametes and supports the sporophyte, which is what makes it the dominant phase. Liverworts show the same dominance of the haploid body, though their body stays thalloid and dorsiventral instead of becoming leafy.