NCERT Solutions for Class 11 Biology Chapter 3 Plant Kingdom

NCERT
SOLUTIONS
CLASS - 11TH

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Class : 11th
Subject : Biology
Chapter : 3
Chapter Name : Plant Kingdom

Q1 What is the basis of classi cation of algae?

Answer. Algae are classi ed into three main classes — Chlorophyceae, Phaeophyceae, and
Rhodophyceae. These divisions are based on the following factors:
(a) Major photosynthetic pigments present
(b) Form of stored food
(c) Cell wall composition
(d) Number of agella and position of insertion Class I — Chlorophyceae
Common name — Green algae
Major pigments — Chlorophylls a and b Stored food — Starch
Cell wall composition — Cellulose
Flagella number and position — 28; equal and apical Class II — Phaeophyceae
Common name— Brown algae
Major pigments — Chlorophylls a and c, and fucoxanthin Stored food — Mannitol and laminarin
Cell wall composition — Cellulose and algin
Flagella number and position — 2; unequal and lateral Class Ill — Rhodophyceae
Common name — Red algae
Major pigments — Chlorophylls a and b, and phycoerythrin Stored food — Floridean starch
Cell wall — Cellulose, pectin, and polysulphate esters Flagella number — Absent

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. Liverwort — In liverworts, the main plant-body is haploid (gametophytic). It bears the
male and female sex organs which produce gametes. These gametes fuse to form a zygote. The
zygote develops on the gametophytic plant-body to form a sporophyte. The sporophyte is
differentiated into the foot, seta, and capsule. Many haploid spores are produced as a result of the
reduction division taking place inside the capsule.
Moss — In mosses, the primary protonema (developed in the rst stage) develops into the
secondary protonema. Both these stages are haploid or gametophytic. The secondary protonema
bears the sex organs which produce gametes. These gametes fuse to form a zygote. The zygote
develops into a sporophyte. Many spores are formed as a result of the reduction division taking
place in the capsule of this sporophyte.
Fern — In ferns, the main plant-body is sporophytic. Its leaves are known as sporophylls and these
bear the sporangia. Reduction division takes place in these sporangia, thereby producing many
spores.

Gymnosperm — In gymnosperms, the main plant-body is sporophytic. They bear two types of
leaves — microsporophylls and megasporophylls. Reduction division takes place in the
microsporangia present on the microsporophylls (producing pollen grains) and on the
megasporangia present on the megasporophylls (producing megaspores).
Angiosperm — In angiosperms, the main plant-body is sporophytic and bears owers. The male
sex organ in the ower is the stamen, while the female sex organ is the pistil. Reduction division
takes place in the anthers of the stamen (producing haploid pollen grains) and in the ovary of the
pistil (producing eggs).

Q3 Name three groups of plants that bear archegonia. Brie y 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.
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.

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. (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

Q5 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- xation on earth by photosynthesis, acting as the primary producers in
aquatic habitats.
(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. Carrageenan is used as an emulsi er in chocolates, paints, and
toothpastes. It is obtained from the red algae.
(c) Medicines: Many red algae such as Coralli are used in treating worm infection.
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 water-
proof paints. A type of resin known as turpentine is obtained from various species of Pinus.

Q6 Both gymnosperms and angiosperms bear seeds, then why are they classi ed separately?

Answer. 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 laments 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. 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 laments 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 owering plants. They have sporophylls that aggregate to form
owers 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.

Q7 What is heterospory? Brie y comment on its signi cance. Give two examples.

Answer. 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 rst in pteridophytes such as Selaginella and Salvinia.

Q8 Explain brie y the following terms with suitable examples:-
(i) protonema
(ii) antheridium
(iii) archegonium
(iv) diplontic
(v) sporophyll
(vi) isogamy

Answer. (i) Protonema — It is the rst stage in the life cycle of a moss, developing directly from
the spore. It consists of creeping, green, branched, and often lamentous structures.
(ii) 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.
(iii) Archegonium — It is the female sex organ present in bryophytes, pteridophytes, and
gymnosperms. In bryophytes and pteridophytes, it generally has a swollen venter and a tubular
neck, and contains the female gamete called the egg.
(iv) Diplontic — It is the term used for the 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.

(v) Sporophyll — In pteridophytes, the sporophytic plant body bears sporangia. These sporangia
are subtended by leaf-like appendages known as sporophylls. In gymnosperms, microsporophylls
and megasporophylls are found. These bear microspores and megaspores respectively.
(vi) 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.

Q9 Differentiate between the following:-
(i) red algae and brown algae
(ii) liverworts and moss
(iii) homosporous and heterosporous pteridophyte
(iv) syngamy and triple fusion

Answer.
(i) red algae and brown algae

(ii) liverworts and moss

(iii) homosporous and heterosporous pteridophyte

(iv) syngamy and triple fusion

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Q10 How would you distinguish monocots from dicots?

Answer.

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

Answer.

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Q12 Describe the important characteristics of gymnosperms.

Answer. Important features of gymnosperms:
1. The term gymnosperm refers to plants with naked seeds (gymnos — naked, sperma — seeds),
i.e., the seeds of these plants are not enclosed in fruits.
2. The plant-body ranges from medium to tall trees and shrubs. The giant redwood tree Sequoia is
one of the tallest trees in the world.
3. The root system consists of tap roots. The coralloid roots present in Cycas are associated with
nitrogen- xing cyanobacteria.

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