Biology Class 11 NCERT Solutions: Chapter 3 Plant Kingdom Part 2

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Q: 3. Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.

Answer:

Archegonium is the female sex organ that produces the female gamete or egg. It is present in the life cycles of bryophytes, pteridophytes, and gymnosperms.

Image showing the groups of plants

Image Showing the Groups of Plants

Image showing the groups of plants

Life cycle of a fern (Dryopteris)

Dryopteris is a common fern with pinnately compound leaves. The main plant-body is sporophytic. Many sporangia are borne on the lower surfaces of its mature leaves. Each sporangium has spore mother cells, which undergo meiosis to produce haploid spores. On maturing, these spores dehisce and germinate to give rise to a heart- shaped gametophyte called prothallus.

The prothallus bears the male and female sex organs called antheridia and archegonia respectively. The antheridia produce sperms that swim in water to reach the archegonia. The egg is produced by the archegonia. As a result of fertilisation, a zygote is formed. The zygote forms an embryo, which in turn develops into a new sporophyte. The young plant comes out of the Archegonium of the parent gametophyte.

Q 3 Image of Life Cycle of a Fern

Q 3 Image of Life Cycle of a Fern

Q 3 Image of Life Cycle of a Fern

Q: 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 fern; Gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.

Answer:

(A) Protonemal cell of a moss - Haploid

(B) Primary endosperm nucleus in a dicot - Triploid

(C) Leaf cell of a moss - Haploid

(D) Prothallus of a fern - Haploid

(E) Gemma cell in Marchantia - Haploid

(F) Meristem cell of a monocot - Diploid

(G) Ovum of a liverwort - Haploid

(H) Zygote of a fern – Diploid

Q: 5. Write a note on economic importance of algae and gymnosperms.

Answer:

Economic importance of algae

Algae have diverse economic uses. They perform half of the total carbon dioxide- fixation on earth by photosynthesis, acting as the primary producers in aquatic habitats.

Economic importance of algae

Economic Importance of Algae

Economic importance of algae

(A) Food source: Many species of marine algae such as Porphyra, Sargassum, and Laminaria are edible. Chlorella and Spirulina are rich in proteins. Thus, they are used as food supplements.

(B) Commercial importance: Agar is used in the preparation of jellies and ice- cream. It is obtained from Gelidium and Gracilaria. Carrageenin is used as an emulsifier in chocolates, paints, and toothpastes. It is obtained from the red algae.

(C) Medicines: Many red algae such as Corallina are used in treating worm infections.

Economic importance of gymnosperms

Economic importance of gymnosperms

Economic Importance of Gymnosperms

Economic importance of gymnosperms

(A) Construction purposes: Many conifers such as pine, cedar, etc., are sources of the soft wood used in construction and packing.

(B) Medicinal uses: An anticancer drug Taxol is obtained from Taxus. Many species of Ephedra produce ephedrine, which can be used in the treatment of asthma and bronchitis.

(C) Food source: The seeds of Pinus gerardiana (known as chilgoza) are edible.

(D) Source of resins: Resins are used commercially for manufacturing sealing waxes and waterproof paints. A type of resin known as turpentine is obtained from various species of Pinus.

Q: 6. Both gymnosperms and angiosperms bear seeds, then why are they classified separately?

Answer:

Image of the Gymnosperms and Angiosperms

Image of the Gymnosperms and Angiosperms

Image of the Gymnosperms and Angiosperms

Gymnosperms and angiosperms are seed-producing plants with diplontic life cycles. In gymnosperms, the sporophylls are aggregated to form compact cones. The microsporophylls are broad and are not distinguished into filaments and anthers. The megasporophylls are woody and lack the ovary, style, and stigma, because of which the ovules lie exposed. The female gametophyte consists of archegonia. The fertilisation process involves the fusion of a male gamete with the female gamete. Their endosperm is haploid. The produced seeds are naked as there is no fruit formation.

Angiosperms are also known as flowering plants. They have sporophylls that aggregate to form flowers with the perianth. The microsporophylls consist of stamens containing pollen sacs. These sacs bear the male gametes called pollen grains. The megasporophylls are delicate and rolled, forming carpels that contain the ovary, style, and stigma. The ovules are present inside the ovary. The Archegonium is replaced by an egg apparatus. Two male gametes enter the egg apparatus at the time of fertilisation. One male gamete fertilises the egg and the other fuses with the diploid secondary nucleus to form an endosperm. The resulting endosperm is thus triploid. In addition, in angiosperms, the development of seeds takes place inside the fruits.

Gymnosperms and angiosperms bear seeds

Gymnosperms and Angiosperms Bear Seeds

Gymnosperms and angiosperms bear seeds

Q: 7. What is heterospory? Briefly comment on its significance. Give two examples.

Answer:

Image showing the heterospory

Image Showing the Heterospory

Image showing the heterospory

Heterospory is a phenomenon in which two kinds of spores are borne by the same plant. These spores differ in size. The smaller one is known as microspore and the larger one is known as megaspore. The microspore germinates to form the male gametophyte and the megaspore germinates to form the female gametophyte. The male gametophyte releases the male gametes and these reach the female gametophyte to fuse with the egg. The development of the zygote takes place inside the female gametophyte.

This retention and germination of the megaspore within the megasporangium ensures proper development of the zygote. The zygote develops into the future sporophyte. The evolution of the seed habit is related to the retention of the megaspore.

Heterospory is thus considered an important step in evolution as it is a precursor to the seed habit.

Heterospory evolved first in pteridophytes such as Selaginella and Salvinia.