Chapter 3 : Plant Kingdom

Class 11 Biology Chapter 3 Plant Kingdom Exercise Questions and Answers :

1. What is the basis of classification of algae?

Answer :  Algae classification is based on various criteria: their habitat (aquatic, terrestrial, or symbiotic), wide variability in form and size, diverse reproductive methods (vegetative, asexual, sexual), and pigmentation (green, brown, red). These criteria help organize algae into different classes, such as Chlorophyceae (green algae), Phaeophyceae (brown algae), and Rhodophyceae (red algae), providing a comprehensive understanding of their characteristics and diversity.

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 ?

Answer :  Reduction division, also known as meiosis, takes place at specific stages in the life cycles of various plants:

Liverwort :Reduction division (meiosis) occurs in the sporophyte phase, within the sporangium located on top of the sporophyte.

Moss : Similar to liverworts, meiosis takes place in the sporangium of the sporophyte generation.

Fern : Reduction division (meiosis) occurs in specialized structures called sporangia, which are typically found on the undersides of fern fronds.

Gymnosperm : In gymnosperms, meiosis takes place in the sporangia, which are located on the sporophylls. These sporangia are typically organized into structures like cones.

Angiosperm: In angiosperms, meiosis occurs in the anthers of the stamen, where microsporangia produce microspores (pollen), and in the ovules contained within the ovary, where megasporangia produce megaspores. Meiosis also takes place during the formation of gametes (pollen and egg cells) within the flower

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

Answer : Three groups of plants that bear archegonia are:

Bryophytes: This group includes mosses, liverworts, and hornworts. Bryophytes are non-vascular plants and represent one of the earliest land plants.

Moss Life Cycle:

(a) Mosses exhibit alternation of generations, with both gametophyte and sporophyte stages.

(b) The gametophyte, which is the dominant phase, consists of leafy structures that bear male (antheridia) and female (archegonia) reproductive organs.

(c) Sperm produced in the antheridia swim to the archegonia, where they fertilize eggs, forming diploid zygotes.

(d) The zygotes develop into sporophytes, which are elongated structures with a foot, seta, and capsule at the tip.

(e) Within the capsule, reduction division (meiosis) occurs, leading to the formation of haploid spores.

(f) When mature, the sporophyte capsule releases spores, which disperse into the environment.

(g) Spores germinate and grow into protonemal filaments, which give rise to new gametophytes.

(h) This cycle continues as gametophytes produce gametes, leading to the formation of new sporophytes, completing the 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.

Answer : The ploidy of the mentioned cell types are :

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 .

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

Answer :  Importance of algae :

(a) Algae contribute to fixing a significant portion of Earth's carbon dioxide through photosynthesis, helping reduce greenhouse gases.

(b) Algae photosynthesis increases dissolved oxygen levels in aquatic environments, benefiting aquatic life.

(c) Algae are fundamental as primary producers, forming the base of aquatic food chains for animals.

(d) Several species of marine algae, like Porphyra, Laminaria, and Sargassum, serve as direct food sources for humans.

(e) Certain marine brown (algin) and red (carrageenan) algae produce water-holding substances, used in various commercial applications.

(f) Agar, derived from Gelidium and Gracilaria algae, is used in microbiology for growing microbes and in food preparations like ice-creams and jellies.

(g) Chlorella, a unicellular alga rich in proteins, is used as a dietary supplement, even by astronauts and space travelers.

Importance of  gymnosperms :

(a) Gymnosperms, such as pines and firs, provide high-quality wood used in construction, furniture, and paper production.

(b) Conifers are a source of resin, which yields turpentine used in adhesives, varnishes, and paint production.

(c) Some gymnosperms are used in landscaping and horticulture for their attractive appearance.

(d) Ginkgo biloba, a gymnosperm, is known for its medicinal properties, used in traditional medicine to improve circulation and cognitive function.

(e) Pine nuts, obtained from certain pine species, are used in culinary dishes and as a source of nutrition.

(f) Certain cycads are popular ornamental plants in gardens and landscapes, contributing to the horticulture industry

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

Answer : Gymnosperms and angiosperms, while both producing seeds, are classified separately based on several fundamental differences in their reproductive structures and life cycles.

Gymnosperms :

(i) Gymnosperms have "naked" seeds, which means their seeds are not enclosed within a fruit.

(ii) They produce seeds on the surface of cone scales or similar structures.

(iii) Gymnosperms often have needle-like or scale-like leaves.

(iv) The male gametophyte (pollen) is typically carried by the wind for pollination.

(v) Gymnosperms have a less complex flower structure compared to angiosperms.

Angiosperms (Flowering Plants) :

(i) Angiosperms have seeds that are enclosed within a fruit, providing protection and facilitating seed dispersal.

(ii) They produce a wide variety of flowers, often with specialized structures for pollination.

(iii) Angiosperms have a more complex vascular system, including vessel elements in their xylem.

(iv) The male gametophyte (pollen) often relies on animals, such as insects or birds, for pollination.

(v) Angiosperms are the most diverse and abundant group of plants, with a wide range of species and adaptations.

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

Answer :  Heterospory is a reproductive strategy observed in certain plants, such as Selaginella and Salvinia, where two distinct types of spores, macrospores (large) and microspores (small), are produced. These spores give rise to female and male gametophytes, respectively. In heterosporous plants, female gametophytes are retained on the parent sporophytes for variable periods, and zygotes develop into young embryos within these female gametophytes. Heterospory is a significant evolutionary step because it is a precursor to the development of the seed habit, which offers numerous advantages for plant reproduction and survival.

Two examples of heterospory are  Selaginella and Salvinia .

8. Explain briefly the following terms with suitable examples:-

(i) protonema

(ii) antheridium

(iii) archegonium

(iv) diplontic

(v) sporophyll

(vi) isogamy

Answer :  (i) Protonema:

(a) Protonema is the first stage in the life cycle of mosses and some liverworts.

(b) It is a filamentous or thalloid structure that develops from a spore and serves as the initial form of the gametophyte.

Example: In mosses, protonema is the early, thread-like structure that later gives rise to the leafy moss plant.

(ii) Antheridium:

(a) An antheridium is the male reproductive structure found in bryophytes, such as mosses and liverworts.

(b) It produces sperm cells, also known as antherozoids.

Example: In mosses, antheridia are flask-shaped structures that release antherozoids into water for fertilization.

(iii) Archegonium:

(a) An archegonium is the female reproductive structure in bryophytes and other non-vascular plants.

(b) It contains the egg cell and serves as the site for fertilization.

Example: In mosses, archegonia are vase-shaped structures with a long neck canal that leads to the egg cell.

(iv) Diplontic:

(a) Diplontic is a life cycle characteristic where the diploid (2n) phase dominates the life cycle, and the haploid (n) phase is reduced.

(b) In a diplontic life cycle, the multicellular diploid sporophyte is the prominent stage.

Example: Seed plants, like conifers and flowering plants (angiosperms), exhibit a diplontic life cycle.

(v) Sporophyll:

(a) A sporophyll is a leaf or leaf-like structure in some plants that bears sporangia, which produce spores.

(b) Sporophylls are commonly found in seedless vascular plants and gymnosperms.

Example: In ferns, sporophylls are modified leaves that carry sporangia on their undersides.

(vi) Isogamy:

(a) Isogamy is a type of sexual reproduction in which gametes (sperm and egg) are similar in size and structure.

(b) It is often found in some algae and lower plants.

Example: In the green alga Chlamydomonas, isogamy occurs when both the "+" and "-" gametes are flagellated and nearly identical in size and shape, allowing them to fuse during fertilization.

9. Differentiate between the following:-

(i) red algae and brown algae

(ii) liverworts and moss

(iii) homosporous and heterosporous pteridophyte

Answer :  (i) Red Algae and Brown Algae:

Characteristic	Red Algae	Brown Algae
Color	Typically red due to pigments like phycoerythrin and phycocyanin.	Typically brown due to pigments like fucoxanthin.
Habitat	Mostly marine, found in deeper waters, can also be found in freshwater.	Mostly marine, found in shallower coastal regions.
Cell Wall Composition	Cell walls contain agar and/or carrageenan, which are used in the food industry.	Cell walls contain cellulose and alginates.
Reproduction	They can be both sexual and asexual, with complex life cycles.	Typically reproduce sexually throughalternation of generations.

(ii) Liverworts and Moss:

Characteristic	Liverworts	Moss
Habitat	Liverworts can be found in a variety of environments, including damp soil, rocks, and tree trunks.	Mosses are commonly found in moist, shaded areas such as forests, and also in wetlands and tundra.
Leaf Structure	Liverworts have simple, lobed, or thalloid leaf structures without a midrib.	Mosses typically have a more complex leaf structure with a midrib.
Reproduction	They reproduce through spores and can also exhibit asexual reproduction.	Mosses reproduce through spores in capsules located on stalks.
Size	Liverworts are generally smaller and simpler in structure.	Mosses tend to be larger, with more diversity in size and structure.

(iii) Homosporous and Heterosporous Pteridophyte :

Characteristic	Homosporous Pteridophyte	Heterosporous Pteridophyte
Spore Types	Produces a single type of spore, which is usually similar in size and shape.	Produces two different types of spores: microspores (small) and megaspores (larger).
Gametophyte	The gametophyte that develops from the spore is bisexual, containing both male and female reproductive structures.	Heterosporous pteridophytes have separate male and female gametophytes. The male gametophyte develops from microspores, and the female gametophyte develops from megaspores.
Examples	Examples include most ferns, which are homosporous.	Examples include plants like Selaginella and Isoetes, which are heterosporous

10. 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 :

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

11. Describe the important characteristics of gymnosperms .

Answer : The important characteristics of gymnosperms are :

(i) Gymnosperms are known as "naked-seeded" plants because their seeds are not enclosed in fruit or ovaries.

(ii) They produce microspores and megaspores in specialized structures.

(iii) These spores are produced on sporophylls, which are modified leaves.

(iv) Sporophylls arrange spirally to form male and female cones on the same plant.

(v) Pollen grains develop into pollen tubes, releasing male gametes in the ovules.

(vi) Male gametes fuse with egg cells in the ovules.

(vii) Zygotes develop into embryos within the ovules.

(viii) Ovules mature into seeds after fertilization.