NCERT Solutions for Class 11 Biology Chapter 3 Plant Kingdom

Q1. What is the basis of the classification of algae?

Answer:

Algae are chlorophyll-containing thallus-bearing plants characterised by the absence of the embryo stage. A variety of algae are found in a variety of habitats. The various types of algae are classified based on their pigments, flagellation and the reserve food material. Based on these criteria, algae are of three types, i.e. red algae, brown algae and green algae.

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 a 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 a 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.

Q3. Name the three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.

Answer:

Three groups of plants that have archegonia are given below:

• Bryophytes
• Pteridophytes
• Gymnosperms.

The life cycle of a pteridophyte then consists of two morphologically distinct phases:

(i) The gametophytic phase

(ii) The sporophytic phase.

These two phases come one after another in the life cycle of a pteridophyte, and this phenomenon is called alternation of generation. The gametophyte is a haploid with a single set of chromosomes. It produces male sex organs, antheridia and female sex organs, archegonia.

(i) The antheridia may be embedded or projecting types. Each antheridium has a single-layered sterile jacket enclosing a mass of astrocytes.

(ii) The astrocytes are flask-shaped, sessile or shortly stalked and differentiated into globular venters and tubular necks.

(iii) The diploid zygote is the first cell of the sporophytic generation. It is retained inside the archegonium and forms the embryo.

(iv) The antherozoids, after liberation from antheridium, reach up to the archegonium fuse with the egg and form a diploid structure known as zygotes.

(v) The archegonium contains a large egg, which is non-motile.

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 lipids, protein, vitamins, minerals, etc.

2. Chlorella and Caulerpa are also used to obtain antibiotics.

3. Several 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, so 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 gametophytes 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.

Q8. Explain briefly the following terms with suitable examples

(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.

Q8. Explain briefly the following terms with suitable examples

(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 the neck contains neck canal cells. Archegonium also contains the female gamete which is called egg.

Q8. Explain briefly the following terms with suitable examples

(4) diplontic

Answer:

Diplontic- This is a term utilised 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.

Q8. Explain briefly the following terms with suitable examples

(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.

Q8. Explain briefly the following terms with suitable examples

(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:

Q9. Differentiate between the following:- (ii) liverworts and moss

Answer:

Differences between liverworts and mosses are as follows

Q9. Differentiate between the following:- (iii) homosporous and heterosporous pteridophyte

Answer:

Q10. Match the following (column I with column II)
Column I Column II
(a) Chlamydomonas (i) Moss
(b) Cycas (ii) Pteridophyte
(c) Selaginella (iii) Algae
(d) Sphagnum (iv) Gymnosperm

Answer:

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

Column I Column II
(a) Chlamydomonas (iii) Algae
(b) Cycas (iv) Gymnosperm
(c) Selaginella (ii) Pteridophyte
(d) Sphagnum (i) Moss

Q11. 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.

4. Microsporangia give rise to microspores or pollen grains whereas megasporangia form megaspores. The male and female gametophytes are formed within micropores and megaspores.

5. Female gametophyte contains archegonia. The male gametophyte produces only two male gametes or sperms.

6. The pollination is direct and is accomplished by wind i.e. anemophily. A pollen tube is formed in gymnosperms. I tt is called siphonogamy.

7. Seeds contain endosperm.