NCERT Solutions for Class 11 Biology Chapter 3 - Plant Kingdom

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:

In the life cycle of a liverwort reduction division takes place in the capsule for the formation of haploid spores that will grow into gametophytic thallus after germination. In mosses, the gametes fertilise and a zygote is formed. The zygote develops into the sporophyte. In the capsule of the sporophyte, reduction division takes place and haploid spores are formed which on germination give rise to gametophytic thallus. In ferns, reduction division takes place in the sporangia present on leaves for the production of spores. Gymnosperms, which have sporophytic plant bodies show reduction division in their microsporangia and megasporangia for the formation of microspores and megaspores. In the case of angiosperms, the main plant body is diploid and reduction division occurs for the formation of gametes. Therefore, in the life cycle of an angiosperm, reduction division takes place in the anther and ovary at the time of microspore and megaspore formation respectively.

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 ferm; gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.

Answer:

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

Answer:

Economic importance of algae

1. Green algae such as Ulva, Caulerpa, Enteromorpha, Chlorella etc are used as food rich in lipid, protein, vitamins, minerals etc.
2.  Chlorella and Caulerpa are used to obtain antibiotics also.
3. A number of green algae such as Chlamydomonas, Chlorella, Scenedesmus etc are used in sewage oxidation tanks.

Economic importance of Gymnosperms

1. The seeds of Pinus gerardiana are roasted and eaten.
2. The softwood of gymnosperms is used in the construction of furniture, plywood, packing cases, match sticks, railway sleepers etc.
3.  The wood from Picea, Pinus, Larix and Abies is used in the manufacture of paper.
4.  Pine needles are used to make fibre boards.
5. Resins containing terpenes, resin acids and esters can be obtained from gymnosperms. Resins are used in waterproofing, sealing joints etc.
6. A drug called ephedrine is extracted from Ephedra which is a gymnosperm. This drug is useful in respiratory ailments such as asthma.

Q6. Both gymnosperms and angiosperms bear seeds, then why are they classified separately?

Answer:

Both gymnosperms and angiosperms come under the group spermatophyta or seed- bearing plants. However, angiosperms and gymnosperms are classified separately in spermatophyta because gymnosperms possess naked seeds i.e. their seeds are not enclosed in the ovary whereas angiosperms possess seeds that are enclosed in the ovary.

Q7. What is heterospory? Briefly comment on its significance. Give two examples.

Answer:

Heterospory- It refers to the existence of two types of meiospores i.e. microspores and megaspores in a single plant. These microspores and megaspores are formed respectively within microsporangia and megasporangia which in turn are borne on two distinct sporophylls called microsporophylls and megasporophylls respectively. The microspores and megaspores upon germination give rise to male and female gametophyte respectively. The megaspore is retained in megasporangia and it ensures proper development of the zygote. which is formed after the fusion of microgametes with the megagametes. The zygote is retained on the plant and it is considered to be a precursor of seed habit.

Significance of heterospory- Heterospory is considered to be an important step in evolution as it is a precursor of seed habit which is seen in higher plants. Heterospory was first observed in pteridophyte Selaginella and Salvinia .
 

Q8. Explain briefly the following terms with suitable examples:-

1. protonema

Answer:

Protonema- It refers to the creeping, green, branched, often filamentous structure which is formed directly after the germination of moss spore. It represents the first stage in the life cycle of moss. Protonema is short-lived and it grows prostrate on the surface. Protonema bears rhizoids for the absorption of materials.

2. antheridium

Answer:

Antheridium- It is the male sex organ found in bryophytes, pteridophytes and some algae. Antheridium encloses a mass of cells that give rise to male gametes. Generally, antheridium remains enclosed by a jacket of sterile cells.

3. archegonium

Answer:

Archegonium- It is female sex organ found in bryophytes, pteridophytes and gymnosperms. Based on the presence of archegonium, these three groups are referred to as archegoniate. It generally possesses a swollen venter and a tubular neck. The venter possesses ventral canal cells and neck contains neck canal cells. Archegonium also contains the female gamete which is called egg.

4. diplontic

Answer:

Diplontic- This is a term utilized for depicting the life cycle of angiosperms and gymnosperms. In this type of life cycle, the plant body is represented by a diploid plant, i.e. sporophyte. It bears sex organs that produce male and female gamete. The gametophyte is of reduced type and it is dependent on the sporophyte. The male and female gametes fuse and form zygote which develops on the diploid plant.

5. sporophyll

Answer:

Sporophylls- These refer to leaf-like appendages bearing sporangia in pteridophytes, gymnosperms etc. Sporophylls can be either microsporophylls or megasporophylls and respectively they can form either microsporangia or megasporangia.

 

6. isogamy

Answer:

Isogamy- It refers to the process of fertilisation of two gametes which are exactly similar to each other in morphology, physiology, anatomy etc. Such gametes are called isogametes.

Q9. Differentiate between the following:-
 

(i) red algae and brown algae
 

Answer:

Differences between red algae and brown algae are as follows:

(ii) liverworts and moss
 

Answer:

Differences between liverworts and mosses are as follows

(iii) homosporous and heterosporous pteridophyte

Answer:

(iv) syngamy and triple fusion

Answer:

The differences between syngamy and triple fusion are as follows:

Q10. How would you distinguish monocots from dicots?

Answer:

Differences between monocots and dicots are as follows:

Q11. Match the following (column I with column II)

Column I Column II

1. Chlamydomonas (i) Moss
2. Cycas (ii) Pteridophyte
3. Selaginella (iii) Algae
4. Sphagnum (iv) Gymnosperm

Answer:

Correct matching is (a)-(iii), (b)-(iv), (c)-(ii), (d)-(i)

Column I Column II

1. Chlamydomonas (iii) Algae
2. Cycas (iv) Gymnosperm
3. Selaginella (ii) Pteridophyte
4. Sphagnum (i) Moss

Q12. Describe the important characteristics of gymnosperms

Answer:

Important characteristics of gymnosperms

1. Gymnosperms are seed plants in which the seeds remain exposed over the surface of megasporophylls.
2. Gymnosperms are represented by 900 living species.
3. Gymnosperms are perennial and woody plants (either trees or bushes). The xylem of gymnosperms does not possess vessels except in Gnetum. Phloem is without companion cells and sieve tubes.
4. Two types of sporophylls occur in gymnosperms. These are microsporophylls and megasporophylls. The microsporophylls aggregate to form male strobili or cone while megasporophylls aggregate to form female strobili or cone. Microsporangia and megasporangia are borne on microsporophylls and megasporophylls respectively.
5. Microsporangia give rise to microspores of pollen grains whereas megasporangia forms megaspores. The male and female gametophytes are formed within microspores and megaspores.
6. Female gametophyte contains archegonia. The male gametophyte produces only two male gametes or sperms.
7. The pollination is direct and is accomplished by wind i.e. anemophily. A pollen tube is formed in gymnosperms. It is called siphonogamy.
8. Seeds contain endosperm.