NCERT Solutions for Class 11 Biology Chapter 3: Plant Kingdom

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1. What is the basis of classification of algae?

Ans. The presence or absence of pigments is the main basis of classification of algae. Based on this feature, algae can be classified as:

(a) Chlorophyceae: Chlorophyll a and b are present in them and impart green colour. This group includes ‘blue-green algae’.

(b) Phaeophyceae: Chlorophyll a and c and fucoxanthin are present. Fucoxanthin imparts brown colour. Phaeophyceae are also called ‘brown algae’.

(c) Rhodophyceae: Chlorophyll a and d and phycoerythrin are present. Phycoerythrin imparts red colour. Rhodophyceae are also called ‘red algae’.

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?

Ans. Time and location of reduction division in the life cycle of:

(a) Liver wort: It takes place inside the capsule at the time of spore production.

(b) Moss: Reduction division takes place inside the capsule at the time of spore formation.

(c) Ferns: It takes place in the sporangium in the leaves at the time of spore formation.

(d) Gymnosperm: Reduction division takes place in the sporangium born on sporophyte of cone.

(e) Angiosperm: Reduction division takes place at the time of gamete formation in male and female gametophyte during sexual reproduction.

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

Ans. Archegonia are the female sex organs that produce the female gamete or egg. It is present in the life cycles of Bryophytes, Pteridophytes and Gymnosperms.

Life cycle of a Pteridophyte: The life cycle of a pteridophyte consists of two morphologically distinct phases: These are gametophytic phase and sporophytic phase. These two phases come one after another in the life cycle of a pteridophyte. This phenomenon is called alternation of generation. The gametophyte is haploid with single set of chromosomes. It produces male sex organs antheridia and female sex organs archegonia.

(a) The antheridia may be embedded or projecting type. Each antheridium has single layered sterile jacket enclosing a mass of androcytes.

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

(c) The antherozoids, after liberation from antheridium, reaches up to the archegonium, fuses with the egg and forms a diploid structure known as zygote.

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

(e) The embryo grows and develops to form sporophyte which is differentiated into roots, stem and leaves.

(f) At maturity the plant bears sporangia, which encloses spore mother cells.

(g) Each spore mother cell gives rise to four haploid spores which are usually arranged in tetrads.

(h) The sporophytic generation ends with the production of spores and each spore is the first cell of gametophytic generation because it germinates to produce gametophyte and completes its life cycle.

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.

Ans. Ploidy of the following is given below:

(a) Protonemal cell of a moss – Haploid

(b) Primary endosperm nucleus in a dicot – Triploid

(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

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

Ans. Economic importance of algae and gymnosperms:

Importance of Algae:

(a) Algae use photosynthesis to fix carbon dioxide.

(b) Food is made from marine algae. For example, Laminaria and Sargassum.

(d) Chlorella, an alga, is eaten by the space explorers as a dietary source.

(e) They increase the amount of dissolved oxygen in their immediate environment.

(f ) They produce rich chemicals that serve as food for aquatic creatures.

Importance of Gymnosperms:

(a) Gymnosperms are utilised as decorative plants. Some are bonsai trees that can be found in formal gardens.

(b) Conifers produce turpentine and resins.

(d) Fibres from these plants are used to make paper pulp.

(e) Gymnosperm seeds are utilised in bakery items and other foods.

(f ) Used to make silk and other fabrics.

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

Ans. The seeds of gymnosperms are naked, while those of angiosperms are covered. Hence, they are kept in different groups.

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

Ans. Heterospory refers to the production of two different types of spores in the same plant. Its significance is following:

(a) In gymnosperms and angiosperms, heterospory stimulates seed development.

(b) It is necessary for male and female gametophyte differentiation. Salvinia and Selaginella are two examples.

8. Explain briefly the following terms with suitable examples:

(a) protonema

(b) antheridium

(d) diplontic

(e) sporophyll

(f) isogamy

Ans. (a) Protonema: It forms the first stage in the life cycle of a moss which develops directly from the spore. It consists of creeping, green, branched, and often filamentous structures.

(b) Antheridium: It is the male sex organ present in bryophytes and pteridophytes and is surrounded by a jacket of sterile cells. It encloses the sperm mother cells, which give rise to the male gametes.

(c) Archegonium: It is the female sex organ present in bryophytes, pteridophytes, and gymnosperms. In bryophytes and pteridophytes, it is multicellular and generally has a swollen venter and a tubular neck, where neck consists of neck canal cells and venter contains venter canal cells and egg.

(d) Diplontic: It is the term used for life cycles of seed-bearing plants (gymnosperms and angiosperms). In these plants, the diploid sporophyte is dominant, photosynthetic, and independent. The gametophyte is represented by a single-celled (or a few-celled) structure.

(e) Sporophyll: It bears sporangia in pteridophytes. These sporangia are subtended by leaf-like appendages known as Sporophyll. In gymnosperms, microsporophyll and megasporophylls are found. These bear microspores and megaspores respectively.

(f) Isogamy: It is a type of sexual reproduction involving the fusion of morphologically similar gametes. This means that the gametes are of the same size, but perform different functions. This type of reproduction is commonly observed in Spirogyra.

9. Differentiate between the following:

(a) Red algae and brown algae

(b) Liverworts and mosses

(d) Syngamy and triple fusion

Ans. (a) Differences between Red Algae and Brown Algae.

Red Algae	Brown Algae
Red algae are grouped under the class Rhodophyceae.	Brown algae are grouped under the class Phaeophyceae.
They contain floridean starch as reserve food.	They contain mannitol or laminarin as reserve food.
They contain the photosynthetic pigments chlorophyll (a) and (d), and phycoerythrin.	They contain the photosynthetic pigments chlorophyll (a) and (c), and fucoxanthin.
E.g.: Polysiphonia, Gelidium, etc.	E.g.: Sargassum, Laminaria, etc.

(b) Differences between Liverworts and Mosses:

Liverworts	Mosses
They have unicellular rhizoids.	They have multicellular rhizoids.
They are generally thalloid, with dichotomous branching.	They are foliage, with lateral branching.
Gemma cups are present.	Gemma cups are absent.
Sporophyte has very little photosynthetic tissue.	Sporophyte has abundant photosynthetic tissue.
E.g.: Marchantia, Riccia, etc.	E.g.:, Bartramia pomiformis (Apple moss), Sphagnum.

Homosporous Pteridophytes	Heterosporous Pteridophytes
They bear spores that are of the same type.	They bear two kinds of spores – microspores and megaspores.
They produce bisexual gametophytes.	They produce unisexual gametophytes.
E.g.: Lycopodium	E.g.: Selaginella

(d) Differences between Syngamy and Triple Fusion:

Syngamy	Triple Fusion
It is the process of fusion of the male gamete with the egg in an angiosperm.	It is the process of fusion of the male gamete with the diploid secondary nucleus in an angiosperm.
A diploid zygote is formed as a result of syngamy.	A triploid primary endosperm is formed as a result of triple fusion.

10. How would you distinguish monocots from dicots?

Ans. Differences between Monocots and Dicots:

Monocots	Dicots
Embryo with single cotyledon.	Embryo with two cotyledons.
Flower parts in multiples of three.	Flower parts in multiples of four or five.
Major leaf veins parallel.	Major leaf veins reticulated.
Stem vascular bundles are scattered.	Stem vascular bundles present in a ring.
Roots are adventitious type.	Roots develop from radicle.
Secondary growth absent.	Secondary growth often present.