1. What is the basis of classification of a lgae? 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? 3. Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them. 4. 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 ferm; gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern. Write a note on economic importance of algae and gymnosperms. 6. Both gymnosperms and angiosperms bear seeds, then why are they classified separately? 5. 7. What is heterospory? Briefly comment on its significance. Give two examples.
Answers
Answer:
1. Algae are classified based on their size, shape, pigmentation, storage products, type of habitat, and the presence of flagella.
2. Reduction division takes place in the life cycle of a liverwort during the meiotic division of its gametes, in a moss during the meiotic division of its spores, in a fern during the meiotic division of its gametes, in a gymnosperm during the meiotic division of its microspores, and in an angiosperm during the meiotic division of its megaspores.
3. Three groups of plants that bear archegonia are liverworts, mosses, and ferns. In the life cycle of a liverwort, the haploid gametophyte phase is dominant and the sporophyte phase is reduced. The antheridia and archegonia are produced on the gametophyte, and the zygote formed from the fusion of gametes gives rise to a new gametophyte.
4. Protonemal cell of a moss: haploid; Primary endosperm nucleus in dicot: diploid; Leaf cell of a moss: haploid; Prothallus cell of a fern: haploid; Gemma cell in Marchantia: haploid; Meristem cell of monocot: diploid; Ovum of a liverwort: haploid; Zygote of a fern: diploid.
5. Algae have many economic uses. They are used for food such as seaweeds, for medicines and for the production of biochemicals. They are also used to produce biofuels and biodegradable plastics. Gymnosperms are commercially important for timber, fuel, resins, dyes, and medicines.
6. Gymnosperms and angiosperms are classified separately because they differ in their reproductive structures. Gymnosperms produce naked seeds, while angiosperms produce seeds enclosed in a fruit or ovary.
7. Heterospory is the production of two types of spores, megaspores and microspores, in the same plant. It is an evolutionary adaptation that increases the efficiency of fertilization and increases the rate of sporophyte generation. Examples of heterosporous plants include ferns, lycophytes, and some seed plants.