by NCERT Solved Exercise Questions – Class 11 Biology Chapter 3 Plant Kingdom
3.1 What is the basis of classification of algae?
Ans – Algae are categorised into three major groups called Chlorophyceae, Phaeophyceae, and Rhodophyceae.
Chlorophyceae: Green algae is the popular name for the family’s members.
Brown algae, also known as members of the Phaeophyceae family, are most frequently seen in maritime environments.
Red algae is the popular name for rhodophyta.
3.2 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 – Liverwort – The primary plant body in liverworts is haploid (gametophytic). It contains the sex organs that create gametes for both sexes. To create a zygote, these gametes must unite. The zygote grows into a sporophyte on the gametophytic plant body. The foot, seta, and capsule of the sporophyte are distinct. The reduced division that occurs inside the capsule results in the production of many haploid spores.
Moss: The main protonema, which was created in the first stage, transforms into the secondary protonema in mosses. These two stages are both gametophytic or haploid. The sex organs that create gametes are carried by the secondary protonema. To create a zygote, these gametes must unite. A sporophyte emerges from the zygote. The reduction division that takes place in spores results in the formation of many spores.
Fern – The primary plant structure of ferns is sporophytic. Sporophylls, which are its leaves, are where the sporangia are found. These sporangia undergo reduction division, which results in the production of many spores.
Gymnosperm – The primary plant structure in gymnosperms is sporophytic. They produce microsporophylls and megasporophylls, two different types of leaves. Both the microsporangia on the microsporophylls, which produce pollen grains, and the megasporangia on the megasporophylls undergo reduction division (producing megaspores).
Angiosperm – The primary plant body of angiosperms is sporophytic and produces flowers. The stamen and pistil are the male and female sex organs, respectively, in flowers. Both the ovary of the pistil and the anthers of the stamen undergo reduction division to produce haploid pollen grains (producing eggs).
3.3 Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
Ans – The female reproductive organ of the is called archegonia.
1.Bryophytes 2. Plant groupings Pteridophytes and 3. Gymnosperms.
The gymnosperm life cycle: Gymnosperms produce haploid microspores and megaspores; they are heterosporous. The two types of spores are created within oil-sporophyll-borne sporangia that are spirally organised along an axis to form loose or compact strobili or cones.
Microsporangia, or male strobili, are the strobili that contain microsporophylls and microsporangia. The male gametophytic generation produced by the microspores is severely constrained to a small number of cells. Pollen-grain is the name given to this reduced gametophyte. Within the microsporangia, pollen-grain formation occurs.
Those cones Microsporangia, also known as female strobili, are megasporophylls that produce megasporangia or ovules. On the same tree or on other trees, the male or female cones or strobili may be produced. One of the nucellus’ cells differentiates into the megaspore mother cell. The combined form, which has the nucellus shielded by envelopes, is known as an ovule.
Megasporophylls, on which the ovules are carried, may group together to produce female cones. The sporophyte’s primary plant body is where the female cones are carried. Four megaspores are produced by the meiotic division of the megaspore mother cell. A female gametophyte with two or more archegonia, or female sex organs, arises from one of the megaspores contained within the megasporangium (nucleus).
Life cycle of gymnosperm:
1.Gymnosperms produce haploid microspores and megaspores; they are heterosporous.
2. The two types of spores are created in sporangia that are carried by sporophyll and are spirally organised along an axis to form strobili or cones.
3. Microsporangiate or male strobili are the strobili that contain microsporophylls and microsporongia.
4. The male gametophytic generation produced by the microspores is extremely diminished and limited to a small number of cells.
5. The pollen grain is the reduced gametophyte. Within microsporangia, pollen grain formation occurs.
6. Male or macrosporangiate strobili are the cones that produce megasporophylls containing ovules or megasporangia.
7. the same tree or other trees may bear the male or female cones or strobili.
3.4 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
Protonemal cell of a moss – haploid.
Primary endosperm nucleus in dicot – triploid.
Leaf cell of a moss – haploid.
Prothallus cell of a fern – haploid.
Gemma cell in Marchantia – haploid.
Meristem cell of monocot – diploid.
Ovum of a liverwort – haploid.
Zygote of a fern – diploid.
3.5 Write a note on economic importance of algae and gymnosperms.
Ans – Algae’s economic value
Numerous commercial applications exist for algae. They serve as the principal producers in aquatic ecosystems and fix half of the planet’s carbon dioxide through photosynthesis.
(a) Food source: A variety of marine algae species, including Porphyra, Sargassum, and Laminaria, can be consumed. Spirulina and chlorella are both high in proteins. They are utilised as food supplements as a result.
(b) commercial importance : Agar is used to make ice cream, jellies, and other foods that are of commercial relevance. It comes from the plants Gelidium and Gracilaria. Carrageenin is a natural emulsifier that is used in toothpaste, paint, and chocolate. Red algae is used to produce it.
(c) Medicines: Worm infections are treated with a variety of red algae, including Corallina.
Gymnosperms are significant economically for the following reasons:
(a) Construction: Soft wood used in construction and packaging is sourced from a variety of conifers, including pine, cedar, and others.
(b) Medical applications: Taxus is used to produce the anticancer medication Taxol. Ephedrine, which is produced by a variety of Ephedra species, is effective in treating bronchitis and asthma.
(c) Food source: Chilgoza, or Pinus gerardiana, seeds can be eaten.
(d) Resins’ source: Resins are produced commercially and utilised to create paints that are waterproof and sealing waxes. Many Pinus species are used to produce turpentine, a form of resin.
3.6 Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
Ans – Gymnosperms are “naked seeded” plants because the ovary wall does not enclose the seeds of angiosperms, which are “enclosed seeds” because the ovary wall does.
3.7 What is heterospory? Briefly comment on its significance. Give two examples.
Ans – Heterospory refers to the co-occurrence of two distinct spore types within a single plant. The size of these spores varies. The smaller of these spores is known as a microspore, and the larger one as a megaspore.
Effects of heterospory
(1) Heterospory is related to gametophyte sexual differentiation; a microspore grows into a male gametophyte, whilst a megaspore develops into a female gametophyte.
(2) Because spores in homosporous pteridophytes must germinate in soil, they are more susceptible to environmental issues. The spores of heterosporous pteridophytes germinate inside the sporangium, where the gametophytes are kept for varying lengths of time. Therefore, a gametophyte that is germination has a higher probability of survival. This establishes the framework for angiosperms and gymnosperms’ complete retention of gametophytes within sporophytes.
(3) This incident is regarded as a crucial milestone in the evolution of the seed habit. The first stage of seed habit is thought to be heterospory. Marsilea and Selaginella exhibit a seed habit.
3.8 .Explain briefly the following terms with suitable examples:-
(i) protonema (ii) antheridium (iii) archegonium (iv) diplontic (v) sporophyll (vi) isogamy
Ans – (i) Protonema: A moss or fern spore’s earliest, typically branched, green, and filamentous structure is known as a prototonema. Moss protonema produce buds that eventually become gametophyte plants. The protonema turns into the prothallus in ferns.
(ii) Antheridium: In cryptogams (algae, fungi, bryophytes, etc
The term “antheridium” refers to pteridophytes. It creates male gametes, also known as antherozooids. It could be made up of a single cell or have a wall made up of one or more layers that surrounds the growing gametes in a sterile jacket.
(iii) Archegonium: This multicellular flask-shaped female sex organ is found in many gymnosperms, pteridophytes, and bryophytes. The female gamete, egg, or oosphere is located inside the venter, a dialated base of the organism. Male gametes can swim toward the ozone by liquifying the cells in the archegonium’s small neck.
(iv) Diplontic: This type of life cycle is characterised by the dominance of the photosynthetic diploid sporophyte. A greatly reduced, few-celled gametophyte or just gametes that have undergone meiosis represent the gametophytic phase. such as all plants that produce seeds (gymnosperms and angiosperms).
(v) Sporophyll: This form of sporangia bears leaves. The sporophylls are the typical foliage leaves in ferns, but in other plants, they are changed and form specialised structures like the club-moss strobili, gymnosperms, and angiosperm flowers. Microsporophylls and megasporophylls are the two main forms of sporophylls found in most plants.
(vi) Isogamy: is a form of sexual reproduction in which two identical gametes fuse together. When sexual reproduction occurs, the gametes exhibit equivalent motility and are identical in size and shape (algae).
3.9. Differentiate between the following:-
(i) red algae and brown algae (ii) liverworts and moss (iii) homosporous and heterosporous pteridophyte
(iv) syngamy and triple fusion
Ans – The differences between red algae and brown algae are as :
| Syngamy | Triple fusion | ||
| 1. | It is the process of fusion of the male gamete with the egg in an angiosperm. | 1. | It is the process of fusion of the male gamete with the diploid secondary nucleus in an angiosperm. |
| 2. | A diploid zygote is formed as a result of syngamy. | 2. | A triploid primary endosperm is formed as a result of triple fusion. |
3.10 How would you distinguish monocots from dicots?
Ans – Dicots differ from monocotyledons by having two cotyledons in their seeds instead of just one.
| Characteristic | Monocot | Dicot |
| Morphology | ||
| Roots | Fibrous roots | Tap roots |
| Venation | Generally parallel venation | Generally reticulate venation |
| Flowers | Trimerous flowers | Pentamerous flowers |
| Cotyledons in seeds | One | Two |
| Anatomy | ||
| No. of vascular bundles in stem | Numerous | Generally 2 – 6 |
| Cambium | Absent | Present |
| Leaves | Isobilateral | Dorsiventral |
3.11 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
Ans – column1 column II
(a) Chlamydomonas (iii) Algae
(b) Cycas (iv) Gymnosperm
(c) Selaginella (ii) Pteridophyta
(d) Sphagnum (i) Moss
3.12 Describe the important characteristics of gymnosperms.
Ans – Gymnosperm characteristics of importance:
1.Plants with naked seeds are referred to as gymnosperms (gymnos = naked, sperma = seeds); that is, the seeds of these plants are not protected by fruits.
2. Medium to tall trees and bushes make up the plant body. One of the tallest trees in the world is the enormous redwood tree Sequoia.
3. Tap roots make up the root system. Cycas’ coralloid roots are connected to cyanobacteria that fix nitrogen.
4. The stem might be unbranched or branched (as in Pinus and Cedrus) (as in Cycas).
5. Simple (as in Pinus) or compound leaves are both possible (pinnate in Cycas). The leaves have a thick cuticle, needle-like shape, and depressed stomata. These assist in stopping water loss. Gymnosperms have heterosporous spores,
6. They produce microspores and megaspores, two different types of spores.
7. There are no flowers. Compact male and female cones are created by the arrangement of the microsporophylls and megasporophylls.
8. Pollen grains enter the pollen chamber of the ovule through the micropyle, and wind is the primary method of pollination.
9. The sporophyte is the only source of food for the male and female gametophytes.
10. The haploid endosperms of the seeds are still exposed.
