Gujarat Board GSEB Textbook Solutions Class 11 Biology Chapter 3 Plant Kingdom Textbook Questions and Answers.

Gujarat Board Textbook Solutions Class 11 Biology Chapter 3 Plant Kingdom

GSEB Class 11 Biology Plant Kingdom Text Book Questions and Answers

Question 1.
What is the basis of the classification of algae?
Answer:
Algae are classified based on the colour of algae that is based on the presence or absence of the certain type of pigment that gives algae its colour.

• Chlorophyceae → green algae or blue-green algae due to the presence of pigments chlorophyll a and b
• Phaeophyceae → brown algae due to the presence of pigments chlorophyll a and c and fucoxanthin.
• Rhodophyceae → Red algae due to the presence of phycoerythrin (red colour) and chlorophyll a and d.

Question 2.
When and where does reproduction take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm, and an angiosperm?
Answer:
The plant body of a liverwort is thalloid such as Marchantia. Asexual reproduction in liverworts takes place by fragmentation of thalli, or by the formation of specialized structures called gemmae. The predominant stage of the life cycle of a moss is the gametophyte which consists of two stages:

• protonema
• leafy stage.

Vegetative reproduction in mosses is by fragmentation and budding in the secondary protonema. In sexual reproduction, the sex organs antheridia and archegonia are produced at the apex of the leafy shoots. After fertilization, the zygote develops into a sporophyte, consisting of a foot, seta and capsule. The capsule contains spores. Spores are formed after reductions! division or meiosis. The mosses have an elaborate mechanism of spore dispersal. Common examples of mosses are Funaria, Polytrichum, and Sphagnum.

The Pteridophyta includes the horsetails and the ferns. In the majority of the pteridophytes, all the spores are of similar kinds; such plants are called homosporous. The female gametophytes in these plants are retained on the parent sporophyte for variable periods. The development of the zygotes into young embryos takes place within the female gametophytes. This event is considered an important step in evolution leading to the seed habit. The Pteridophyta is further classified into four classes: psilopsida, lycopsida, sphenopsida, and pteropsida.

The gymnosperms are heterosporous, they produce haploid microspores and megaspores. The two kinds of spores are produced within sporangia that are borne on sporophylls which are arranged spirally along an axis to form lax or compact strobili or cones. The strobili bearing microsporophylls and microsporangia are called microsporangia or male strobili. The microspores develop into a male gametophytic generation which is highly reduced and is confined to only a limited number of cells. This reduced gametophyte is called a pollen-grain. The development of pollen-grains takes place within the microsporangia. The cones bearing megasporophylls with ovules or megasporangia are called microsporangia or female strobili. The male or female cones or strobili may be borne on the same tree (Pinus) or on different trees (Cycas)

Angiosperms are the flowering plants in which the seeds are enclosed by fruits. The male sex organ in a flower is the stamen. Each stamen consists of a slender filament with an anther at the tip. The anthers produce pollen grains following meiosis. The female sex organ in a flower is the pistil or the carpel. The pistil consists of an ovary enclosing one to many ovules. Within ovules are present highly reduced female gametophytes termed embryo-sacs.

The embryo-sacs are haploid. Each embryosac has a 3-celled egg apparatus- one egg cell and two synergids, 3 antipodal cells, and two polar-nuclei. The polar nuclei eventually fuse to produce a diploid secondary – nucleus. Pollen grains after dispersal from the anthers are carried by wind or various other agencies of the stigma of a pistil. This is termed pollination.

Question 3.
Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
Answer:
Bryophytes, pteridophytes, and gymnosperms bear district archegonia.
The life cycle of gymnosperms:
The gymnosperms are heterosporous. They produce haploid microspores and megaspores. The two kinds of spores are produced within sporangia that are borne on sporophylls. Which are arranged spirally along an axis to form lax or compact strobili or cones? The strobili bearing microsporophylls and microsporangia are called microsporangia or male strobili. The microspores develop into a male gametophyte generation which is highly reduced and is comprised of only a limited number of cells. This reduced gametophyte is called a pollen grain. The development of pollen grain take place within the microsporangia.

The cones bearing megasporophylls with ovules or megasporangia are called microsporangia or female strobili. The male or female cones or strobili may be borne on the same tree (pistil) however in cycas male cones and megasporophylls are borne on different trees. The megaspore mother cell is differentiated from one of the cells of the nucellus. The nucellus is protected by envelopes and the composite structure is called an ovule.

The Ovules are borne on megasporophylls which may be discharged to form the female cones. The megaspore mother cell divides mitotically to form four megaspores. One of the megaspores enclosed within the megasporangium (nucellus) develops into a multicellular female gametophyte that bears two or more archegonia or female sex organs. The multicellular female gametophyte is also retained within megasporangium.

Question 4.
Mention the ploidy of the following: protonemal cell of a moss, primary endosperm nucleus in dicot; leaf ceil of a moss; prothallus cell of a fern; gemma cell in Marchantia; meristem ceil of monocot; ovum of a liverwort, and zygote of a fern.
Answer:
(1) Protonemal cell of a moss: The first stage is the protonema stage, which develops directly from a spore. It is a creeping, green, branched, and frequently filamentous stage.

(2) Primary endosperm nucleus in dicot: The pollen tubes enter the embryo-sac where the two male gametes are discharged. One of the male gametes fuses with the egg cell to form a zygote (syngamy). The other male gamete fuses with the diploid secondary nucleus or two haploid polar nuclei (triple fusion) to produce the triploid primary endosperm nucleus (PEN) The zygote develops into an embryo (with one or two cotyledons) and the PEN develops into endosperm which provides nourishment to developing embryo.

(3) Leaf cell of a moss: The second stage is the leafy stage, which develops from the secondary protonema as a lateral bud. They consist of upright, slender axes bearing spirally arranged leaves. They are attached to the soil through multicellular and branched rhizoids. This stage bears the sex organs.

(4) Prothallus cell of a fern: The sporangia produce spores by meiosis in spore mother cells. The spores germinate to give rise to inconspicuous, small but multicellular, free-living, mostly photosynthetic thalloid gametophytes also called prothallus. These gametophytes require cool damp, shady places to grow. The gametophyte bears male and female sex organs called antheridia and archegonia respectively.

(5) Gemma cell in Marchantia: Gemmae are green, multicellular asexual buds, which develop in small receptacles located on the tallies called gemma cups. The gemmae become detached from the parent body and germinate to form new individuals. During sexual reproduction, male and female sex organs are produced either on the same or on different thalli. The sporophyte is differentiated into a foot, seta, and capsule (e.g. Marchantid). After meiosis spores are produced within the capsule. These spores germinate to form-living gametophytes.

(6) Meristem cell of monocot :

1. It is a simple tissue, made up of immature (undifferentiated) cells.
2. The cells are small and isodiametric.
3. The cell wall is thin.
4. Intercellular spaces are very small or absent.
5. Crystals and other cell inclusions are absent
6. The metabolic activities are very high.
7. The cell has the ability to undergo repeated divisions.

(7) Ovum of a liverwort: Asexual reproduction in liverworts takes place by fragmentation of this, or by the formation of specialized structures called gemmae. Gemmae are green, multicellular asexual buds, which develop in small re ‘pentacles located on the thallus called gemma cups. The game become detached from the parent body and germinate to form new individuals. During sexual reproduction, male and female sex organs are produced either on the same or on different thalis. The sporophyte is differentiated into a foot, seta, and capsule. After meiosis sposes are produced within the capsule. These spores germinate to form free-living gametophytes.

(8) Zygote of a fern: Fusion of male gamete with the egg present in the archegonium result in the formation of zygote. Zygote thereafter produces a multicellular well-differentiated sporophyte which is the dominant phase of the pteridophytes. In the majority of the pteridophytes, all the spores are of similar kinds; such plants are called homosporous. The megaspores and microspores germinate and give rise to female and male gametophytes, respectively. The female gametophytes in these plants are retained on the parent sporophyte for a variable period.
The development of the zygotes into young embryos takes place within the female gametophytes. This event is considered an important step in -evolution leading to the seed habit.

Question 5.
Write a note on the economic importance of algae and gymnosperms.
Answer:
Economic importance of Algae:
Algae are useful to man in a variety of ways. At least half of the total carbon dioxide fixation on earth is carried out by algae through photosynthesis. Being photosynthetic they increase the level of dissolved oxygen in their immediate environment. They are of paramount importance as primary producers of energy-rich compounds which form the basis of the food cycles of all aquatic animals.

Many species of Porphyra, Laminaria and Sargassum are among the 70 species of marine algae used as food. Certain marine brown and red algae produce large amounts of hydrocolloids (water-holding substances), e.g., algin (brown algae) and carrageen (red algae) are used commercially. Agar, one of the commercial products obtained from Gelidium and Gracilaria are used to grow microbes and in preparations of ice-creams and jellies. Chlorella and Spirulina are unicellular algae, rich in proteins and are used as food supplements even by space travellers.

Economic Importance of Gymnosperms:
Gymnosperm plants are widely used as ornamental. Conifers are often featured informal gardens and are used for bonsai. Yews and junipers are often low-growing plants cultivated for ground cover. Conifers are effective windbreaks, especially those that are evergreen. Turpentine and resin are derived from conifer resins. Copal, a hardened form of resin from a kauri is used to manufacture paints and Varnishes. Balsam and dammer resin are used in the preparation of mounting media for microscope slides. Resines have medicinal uses.

The fossilized resin of conifers are used to manufacture amber. Commercially useful oils are derived from such conifers as junipers, pines, hemlock, fir, spruces and arborvitae. These oils serve as air freshness, disinfectants, and smell in soaps and cosmetics. Seeds are often food sources. Pine seeds are a delicacy eaten plain or used as a garnish on bakery produces Seeds of Ginkgo and cycads may be poisonous unless detoxified. “Berries” of juniper are used as flavouring. Most plywood is gymnosperms.

Question 6.
Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
Answer:
Because, Gymnosperms sporophylls are aggregated to form cones, whereas in Angiosperms sporophylls are aggregated to form a flower. In gymnosperms, a seed develops exposed to megasporophyll. The fruit is never formed, while in angiosperms seeds develop inside the ovary which matures into a fruit. In gymnosperms ovules lie exposed on the megasporophylls, while in ovules are borne inside the ovary, hence are covered. In gym¬nosperms an ovule is covered by 3 layered integuments with a wide microphone, while in angiosperms an ovule is covered by one or two thin integuments with a narrow microphone. In gymnosperms pollen grains directly enter into the ovule and come to lie over the nucleus, while in angiosperms pollen grains reach the respective organ called stigma.

Question 7.
What is heterospory? Briefly comment on its significance. Give two examples.
Answer:
Pteridophytes produce two kinds of spores. This phenomenon is called heterospory. The microspore is reduced/small male gametophytes produced whereas megaspores are bigger female gametophytes produced. The development of the zygotes into embryos takes place within the female gametophytes. This event is a precursor to the seed habit considered as an important step in evolution.

Question 8.
Explain briefly the following terms with a suitable example:

1. Protoneuia
2. Antheridium
3. Archegonium
4. Diplontic
5. Sporophyll
6. Isogamy

Answer:
(1) Protonema: The predominant stage of the life cycle of a moss is the gametophyte which consists of two stages. The first stage is the protonema stage, which develops directly from a spore. It is a creeping, green, branched, and frequently filamentous stage.

(2) Antheridium: The sex organs in bryophytes are multicellular. The male sex organ is called antheridium.

(3) Archegonium: The female sex organ is called archegonium.

(4) Diplontic: On the other extreme, is the type wherein the diploid sporophyte is the dominant, photosynthetic, independent phase of the plant. The gametophytic phase is represented by the single to few celled haploid gametophytes. This kind of life-cycle is termed diplontic. All seed-bearing plants i.e., gymnosperms and angiosperms, follow this pattern.

(5) Sporophyll: The sporophyte bear sporangia that are subtended by leaf-like appendages called sporophylls.

(6) Isogamy: Sexual reproduction takes place through the fusion of two gametes. These gametes can be flagellated and similar in size (as in (Chlamydomonas) or non-flagellated (non-motile) but similar in size (as in Spirogyra). Such reproduction is called isogamous.

Question 9.
Differentiate between the following:

1. Red algae and Brown algae
2. Liverworts and Moss
3. Homosporous and Heterosporous pteridophyte
4. Syngamy and Triple fusion.

Red Algae:

1. They are mostly marine and include several seaweeds. A few are, however, freshwater (e.g Batrachospermum).
2. They range from microscopic form to about half a meter in length. Their plant body may be Unicellular (e.g. Porphyridium), filamentous (e.g. Steriocystis), a sheet of cells (e.g. Porphyra Chondrus).
3. The cell wall contains sulfated mucopolysaccharides called Phycocolloids, besides cellulose and pectic substances. The important hydrocolloids of red algae are agar, carrageenin, and porphyrin
4. Some red algae accumulate calcium carbonate from seawater and deposit it over their walls. They appear coral-like and are called coralline algae (e.g. Corallina).
5. The stored food in red algae is Floridian starch, somewhat similar to glycogen.
6. Flagellated or motile cells are absent in red algae.
7. Some red algae involve the alter¬nation of haploid and diploid generations during the life cycle.
8. Sexual reproduction occurs by different types of non-motile spores called neutral spores, monospores, carpospores, tetraspores, etc

Brown Algae:

1. They are all marine occurring mainly in cooler seas. Sargassum is an exception occurring in warm seas.
2. Unlike red or green algae unicellular form is not known in brown algae. Some of them are the largest sea plants reaching 40 -60 meters in length e.g. Macrocystis. They may be branched, filamentous (e.g Ectocapus) or flat ribbon-shaped (e.g., Sargassum, Laminaria, Fucus, etc.)
3. The plant body of large forms is often differentiated into holdfast, stipe, and lamina. Some of the larger.
4. Brown algae are commonly found attached by means of their holdfast. A few, such as Sargassum and Fucus are free-floating.
5. The reserve food is in the form of carbohydrates laminarin and lipid.
6. Vegetative reproduction occurs through fragmentation and specialized propagules called nests of cells.
7. Alternation of haploid and diploid generation occurs in some algae during their life cycles. In; some forms, the two generations I am similar in structure.
8. Sexual reproduction varies from isogamy, anisogamy to oogamy, In isogamy and anisogamy both the gametes are motile with heterokont flagellation.

(2) Differences between liverworts and mosses:
Liverworts:

1. They have dorsiventral symmetry.
2. They are generally thalloid, rarely foliage, with dichotomous branching.
3. Rhizoids are unicellular
4. Scales are often present.
5. A filamentous stage is absent.
6. Sporophyte has very little phot­osynthetic tissue
7. Central columella does not occur inside the capsule.
8. Elaters are present in the capsule to assist the dispersal of spores but peristome teeth are absent.

Mosses:

1. They possess radial symmetry.
2. They are usually foliage, with lateral branching.
3. Rhizoids are multicellular.
4. Scales are absent.
5. A filamentous protonema stage is always present.
6. Sporophyte has abundant phot
7. A central columella is present, inside the capsule.
8. Elaterf are absent but peris I tome teeth are present in the capsule to assist the dispersal of spores.

(3) Differences between homosporous and heterosporous pteridophyte:
Homosporous:
Zygote thereafter produces a multicellular well-differentiated sporophyte which is the dominant phase of the pteridophytes. In the majority of the pteridophytes, all the spores are of similar kinds, such plants are called homosporous.

Heterosporous:
Genera like Selaginella and Salvinia which produce two kinds of spores, macro (large) and micro (small) spores, are known as heterosporous

(4) Differences between Syngamy and Triple fusion
Syngamy:
The pollen tubes enter the embryo-sac where the two male gametes are discharged. One of the male gametes fuses with egg cells to form a zygote (Syngamy).

Triple fusion:
The other male gamete fuses with the diploid secondary nucleus or two haploid polar nuclei (triple fusion) to produce the triploid Primary endosperm: nucleus (PEN).

Question 10.
How would you distinguish monocots from dicots?
Answer:
Differences between Monocots and Dicots:

Question 11.
Match the following Column I with Column II

Answer:
a. iii, b. iv, c. ii, d. i.

Question 12.
Describe the important characteristics of gymnosperms.
Answer:
Important characteristics of gymnosperms are

• The gymnosperms are plants in which the ovules are not enclosed by any ovary wall and remain exposed, both before and after fertilization.
• Gymnosperms include medium-sized/tall trees and shrubs.
• Roots are generally tapped roots, some genera have a fungal association in the form of mycorrhiza (Pinus), in their roots, while in some other (Cycas) N₂ fixing cyanobacteria are present.
• Stems are unbranched (Cycad) or branched {Pinus, Cedrus).
• Leaves may be simple or compound. In Cycas, the pinnate leaves persist for a few years.
• Leaves in gymnosperms are well-adapted to withstand extremes of temperature, humidity, and wind.
• In conifers, needle-like leaves reduce surface area. Their thick cuticle and sunken stomata also help to reduce water loss.