NCERT Chapter Exercises
1. What is the basis of classification of algae?
Algae are classified into three main classes (Chlorophyceae, Phaeophyceae, and Rhodophyceae) based on:
- Pigments: Type of photosynthetic pigments present (e.g., Chlorophyll a, b, c, d, fucoxanthin, phycoerythrin).
- Stored Food: The form in which food is stored (e.g., starch, mannitol, floridean starch).
- Cell Wall: Chemical composition of the cell wall.
- Flagella: Number and position of flagellar insertions.
2. When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?
- Liverwort & Moss: In the capsule of the sporophyte (spore mother cells) to form haploid spores.
- Fern: In the sporangia borne on sporophylls (spore mother cells) to form spores.
- Gymnosperm & Angiosperm: In the microsporangia and megasporangia inside the cones/flowers (microspore mother cells and megaspore mother cells) to form pollen and megaspores.
3. Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
Groups: Bryophytes, Pteridophytes, and Gymnosperms.
Life Cycle of Bryophytes: The dominant phase is the haploid gametophyte. It bears sex organs, Antheridia (male) and Archegonia (female). Fusion of gametes forms a diploid zygote, which develops into a multicellular sporophyte attached to the gametophyte. The sporophyte undergoes meiosis to produce haploid spores, which germinate to produce the gametophyte again.
Life Cycle of Bryophytes: The dominant phase is the haploid gametophyte. It bears sex organs, Antheridia (male) and Archegonia (female). Fusion of gametes forms a diploid zygote, which develops into a multicellular sporophyte attached to the gametophyte. The sporophyte undergoes meiosis to produce haploid spores, which germinate to produce the gametophyte again.
4. Mention the ploidy of the following:
- Protonemal cell of a moss: Haploid (n)
- Primary endosperm nucleus in dicot: Triploid (3n)
- Leaf cell of a moss: Haploid (n)
- Prothallus cell of a fern: Haploid (n)
- Gemma cell in Marchantia: Haploid (n)
- Meristem cell of monocot: Diploid (2n)
- Ovum of a liverwort: Haploid (n)
- Zygote of a fern: Diploid (2n)
5. Write a note on economic importance of algae and gymnosperms.
Algae:
Gymnosperms:
- Carry out 50% of earth's CO2 fixation.
- Used as food (e.g., Porphyra, Sargassum).
- Production of Hydrocolloids (Algin, Carrageen) and Agar.
Gymnosperms:
- Provide timber and paper pulp (e.g., Pinus).
- Medicinal uses (e.g., Taxol).
- Edible seeds (e.g., Chilgoza pine).
- Ornamental plants.
6. Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
They are classified separately because in Gymnosperms, the ovules are not enclosed by any ovary wall and remain exposed (naked seeds). In Angiosperms, the seeds are enclosed within fruits (ovules inside ovary).
7. What is heterospory? Briefly comment on its significance. Give two examples.
Heterospory is the production of two kinds of spores: macro (large) and micro (small) spores.
Significance: The development of the zygote into young embryos takes place within the female gametophytes which are retained on the parent sporophyte. This is a precursor to the seed habit, an important step in evolution.
Examples: Selaginella and Salvinia.
Significance: The development of the zygote into young embryos takes place within the female gametophytes which are retained on the parent sporophyte. This is a precursor to the seed habit, an important step in evolution.
Examples: Selaginella and Salvinia.
8. Explain briefly the following terms with suitable examples:
- (i) Protonema: A creeping, green, filamentous juvenile stage in mosses developing from a spore (e.g., Funaria).
- (ii) Antheridium: The male sex organ producing antherozoids (e.g., in Bryophytes).
- (iii) Archegonium: The flask-shaped female sex organ producing an egg (e.g., in Bryophytes).
- (v) Sporophyll: Leaf-like appendages subtending sporangia (e.g., in Ferns).
- (vi) Isogamy: Fusion of gametes that are similar in size (e.g., Spirogyra).
9. Differentiate between the following:
(i) Red Algae vs Brown Algae: Red algae contain r-phycoerythrin and store floridean starch (non-motile). Brown algae contain fucoxanthin and store mannitol/laminarin (motile zoospores).
(ii) Liverworts vs Mosses: Liverworts have a thalloid body (e.g., Marchantia). Mosses have a leafy stage and protonema stage (e.g., Funaria).
(iii) Homosporous vs Heterosporous Pteridophyte: Homosporous produce one type of spore (most ferns). Heterosporous produce two types (Selaginella).
(ii) Liverworts vs Mosses: Liverworts have a thalloid body (e.g., Marchantia). Mosses have a leafy stage and protonema stage (e.g., Funaria).
(iii) Homosporous vs Heterosporous Pteridophyte: Homosporous produce one type of spore (most ferns). Heterosporous produce two types (Selaginella).
10. Match the following (Column I with Column II):
(a) Chlamydomonas — (iii) Algae
(b) Cycas — (iv) Gymnosperm
(c) Selaginella — (ii) Pteridophyte
(d) Sphagnum — (i) Moss
(b) Cycas — (iv) Gymnosperm
(c) Selaginella — (ii) Pteridophyte
(d) Sphagnum — (i) Moss
11. Describe the important characteristics of gymnosperms.
- Ovules are not enclosed by an ovary wall (naked seeds).
- Heterosporous (produce microspores and megaspores).
- Leaves are well-adapted to extreme climates (needle-like, sunken stomata).
- Gametophytes are reduced and not free-living; they remain within the sporangia on the sporophyte.
- Roots often have fungal associations (Mycorrhiza) or Cyanobacteria (Coralloid roots).