EXERCISES

Q1. What is the basis of classification of algae?
Answer: The algae are divided into three main classes — Chlorophyceae (Green algae), Phaeophyceae (Brown algae), and Rhodophyceae (Red algae). The classification is based on four factors:

1. Major Pigments Present: Chlorophyceae – chlorophyll a, b; Phaeophyceae – chlorophyll a, c, fucoxanthin; Rhodophyceae – r-phycoerythrin.
2. Type of Stored Food: Green algae – starch; brown algae – mannitol or laminarin; red algae – floridean starch.
3. Cell Wall Composition: Green algae – cellulose, pectose; brown – cellulose, algin; red – cellulose, pectin, polysulphate esters.
4. Flagella: Green algae – 2–8 equal flagella; brown – 2 unequal, lateral flagella; red algae – no flagella.

Q2. When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?
Answer: Reduction division (meiosis) occurs in the sporophyte generation to form haploid spores.

1. Liverwort & Moss: In the capsule of the sporophyte, before spore release.
2. Fern: In spore mother cells inside sporangia, before spore release.
3. Gymnosperm: In microspore and megaspore mother cells during spore formation.
4. Angiosperm: In pollen (microspore) and embryo sac (megaspore) mother cells during gamete formation.

Q3. Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
Answer: The three groups of plants that possess archegonia are Bryophytes, Pteridophytes, and Gymnosperms.

In Bryophytes such as moss, the main plant body is haploid and is called the gametophyte. It bears the sex organs antheridium (male) and archegonium (female). During fertilisation, the male gametes swim through water to reach the egg inside the archegonium, where they fuse to form a diploid zygote. The zygote develops into a sporophyte consisting of a foot, seta, and capsule, which remains attached to the gametophyte for nourishment. Inside the capsule, meiosis takes place to produce haploid spores. These spores are released and germinate to form new gametophytes, completing the life cycle.

Q4. Mention the ploidy of the following: protonemal cell of a moss; primary endosperm nucleus in dicot, leaf cell of a moss; prothallus cell of a fern; gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.
Answer:

Q5. Write a note on economic importance of algae and gymnosperms.
Answer:

Algae:
Algae are economically important as they are used as food (e.g., Porphyra, Laminaria, Sargassum), and Chlorella serves as a protein-rich food supplement. They provide valuable products like algin (from brown algae), carrageen (from red algae), and agar (from Gelidium and Gracilaria) used in industries, laboratories, and food processing.

Gymnosperms:
Gymnosperms provide timber (from Pinus, Cedrus), resins, and turpentine used in paints and medicines. Some species like Cycas and Ginkgo are ornamental, and edible seeds (e.g., Chilgoza) are also obtained from certain species.

Q6. Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
Answer: They are classified separately due to seed enclosure and reproduction differences:

Q7. What is heterospory? Briefly comment on its significance. Give two examples.
Answer: Heterospory is the phenomenon of producing two different types of spores, namely microspores which develop into male gametophytes and megaspores which develop into female gametophytes. It is found in plants like Selaginella and Salvinia.

The significance of heterospory lies in its evolutionary importance, as it marks a crucial step towards the development of the seed habit. In heterosporous plants, the female gametophyte develops within the parent sporophyte, providing protection and nourishment to the developing embryo. This adaptation eventually led to the formation of seeds in higher plants.

Q8. Explain briefly the following terms with suitable examples:- (i) protonema (ii) antheridium (iii) archegonium (iv) diplontic (v) sporophyll (vi) isogamy
Answer:
(i) Protonema: It is the first stage in the life cycle of mosses, formed from the germination of spores. It is a green, branched, filamentous structure that gives rise to the leafy gametophytic plant. Example: Funaria.

(ii) Antheridium: It is the male reproductive organ that produces male gametes called antherozoids. It is found in plants like Marchantia and ferns.

(iii) Archegonium: It is the female reproductive organ that produces a single egg cell and is typically flask-shaped. It occurs in plants such as Marchantia and Cycas.

(iv) Diplontic: It refers to a type of life cycle in which the diploid sporophyte is the dominant and independent phase, while the gametes represent the only haploid stage. Example: Gymnosperms and Angiosperms.

(v) Sporophyll: It is a leaf-like structure that bears sporangia and is often arranged to form cones or strobili. Example: Selaginella and Cycas.

(vi) Isogamy: It is a type of sexual reproduction involving the fusion of gametes that are morphologically similar but physiologically different. Example: Ulothrix and Spirogyra.

Q9. Differentiate between the following:
(i) red algae and brown algae
(ii) liverworts and moss
(iii) homosporous and heterosporous pteridophyte
Answer:

(i) Red algae and Brown algae: Red algae contain pigments such as chlorophyll a, d, and r-phycoerythrin, and their stored food is floridean starch. They do not possess flagella and are generally found in deep marine waters.
Whereas brown algae contain pigments like chlorophyll a, c, and fucoxanthin, and they store food in the form of mannitol or laminarin. They have two unequal lateral flagella and mostly occur in shallow, cold marine areas.

(ii) Liverworts and Moss: In liverworts, the gametophyte is thalloid and flat, and they possess unicellular rhizoids. Asexual reproduction takes place by gemmae, and their sporophyte is simple in structure.
Whereas in mosses, the gametophyte has two stages, the protonema and the leafy stage, and the rhizoids are multicellular and branched. Asexual reproduction occurs by fragmentation or budding, and their sporophyte is more complex.

(iii) Homosporous and Heterosporous Pteridophyte: Homosporous pteridophytes produce only one type of spore, and their gametophyte is bisexual. They are considered primitive in evolution and do not show the seed habit.
Whereas heterosporous pteridophytes produce two types of spores, microspores and megaspores, and their gametophyte is unisexual. They are more advanced and represent the beginning of the seed habit. Examples include Dryopteris as a homosporous type and Selaginella and Salvinia as heterosporous types.

Q10. Match the following (column I with column II)
Answer:
(a) Chlamydomonas → Algae
(b) Cycas → Gymnosperm
(c) Selaginella → Pteridophyte
(d) Sphagnum → Moss

Q11. Describe the important characteristics of gymnosperms.
Answer: Gymnosperms are “naked-seeded” plants with the following features:

1. Seeds: Ovules are not enclosed by ovary walls; seeds are naked.
2. Plant Body: Dominant diploid sporophyte; tall trees or shrubs (e.g., Sequoia). Roots are tap roots, sometimes mycorrhizal (Pinus) or coralloid (Cycas).
3. Leaves: Adapted to dry conditions; needle-like in conifers with thick cuticle and sunken stomata.
4. Reproduction: Heterosporous; male and female cones bear microspores and megaspores. Gametophytes remain within sporangia on the parent plant.
5. Fertilisation: Air-borne pollen reaches ovule; pollen tube releases male gametes near archegonium. After fertilisation, ovules develop into naked seeds.