Question 1

What is the basis of classification of algae?

Accepted Answer

The presence or absence of pigments is the main basis of classification of algae.Chlorophyceae: Chlorophyll a and b are present in them and impart the green colour. Chlorophyceae are also called as ‘blue-green algae’.Phaeophyceae: Chlorophyll a and c and fucoxanthin are present. Fucoxanthin imparts the brown colour. Phaeophyceae are also called as ‘brown algae’.Rhodophyceae: Chlorophyll a and d and phycoerythrin are present. Phycoerythrin imparts red colour. Rhodophyceae are also called as ‘red algae’.

Question 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?

Accepted 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 first 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 flowers. The male sex organ in the flower 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).

Question 3

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

Accepted 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 as 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.

Question 4

Mention the ploidy of the following:1. Protonemal cell of a moss2. Primary endosperm nucleus in dicot 3. Leaf cell of a moss4. Prothallus cell of a fern5. Gemma cell in Marchantia6. Meristem cell of a monocot 7. Ovum of a liverwort 8. Zygote of a fern

Accepted 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

Question 5

Write a note on economic importance of algae and gymnosperms.

Accepted Answer

Algae have diverse economic uses. They perform half of the total carbon dioxide-fixation 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. Carrageenin is used as an emulsifier in chocolates, paints, and toothpaste. It is obtained from the red algae.(c) Medicines: Many red algae such as Corallina are used in treating worm infections.

Question 6

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

Accepted 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 filaments 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 flowering plants. They have sporophylls that aggregate to form flowers with the perianth. The microsporophylls consist of stamens containing pollen sacs. These sacs bear the male gametes called as 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.

Question 7

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

Accepted 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 first in pteridophytes such as Selaginella and Salvinia.

Question 8

Explain briefly the following terms with suitable examples :(i) Protonema(ii) Antheridium(iii) Archegonium(iv) Diplontic(v) Sporophyll(vi) Isogamy

Accepted Answer

(i) Protonema – It is the first stage in the life cycle of a moss, developing directly from the spore. It consists of creeping, green, branched, and often filamentous 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.

Question 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

Accepted Answer

(i) Red Algae Brown algaeRed algae are grouped under the class Rhodophyceae.Brown algae are grouped under the class Phaeophyceae.They contain floridean starch as stored food. They contain mannitol or laminarin as stored food.They contain the photosynthetic pigments chlorophylls a and d, and phycoerythrin.They contain the photosynthetic pigments chlorophylls a and c, and fucoxanthin.Their cell walls are composed of cellulose, pectin, and phycocolloids.Their cell walls are composed of cellulose and algin.Flagella are absent. Two flagella are present.(ii) Liverworts MossThey have unicellular rhizoids.They have multicellular rhizoids.Scales are present very often.Scales are absent.They are generally thalloid, with dichotomous branching.They are foliage, with lateral branching.Gemma cups are present.Gemma cups are absent.Sporophyte has a very little photosynthetic tissue.Sporophyte has an abundant photosynthetic tissue. (iii) Homosporous HeterosporousThey bear spores that are of the same type.They bear two kinds of spores – microspores and megaspores, differing in size.They produce bisexual gametophytes.They produce unisexual gametophytes. (iv) Syngamy  Triple fusionIt 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.

Question 10

How would you distinguish monocots from dicots?

Accepted Answer

Monocots                                                       Dicots1. Embryo with single cotyledon	           1. Embryo with two cotyledons2. Pollen with single furrow or pore	     2. Pollen with three furrows or pores3. Flower parts in multiples of three	     3. Flower parts in multiples of four or five4. Major leaf veins parallel	                     4. Major leaf veins reticulated5. Stem vascular bundles scattered	      5. Stem vascular bundles in a ring6. Roots are adventitious	                       6. Roots develop from radicle7. Secondary growth absent	                  7. Secondary growth often present

Question 11

Match the following (column I with column II).

Accepted Answer

The correct match is as follows:Column I                                                  Column II(a) Chlamydomonas                             (iii) Algae(b) Cycas                                               (iv) Gymnosperm(c) Selaginella                                       (ii) Pteridophyte(d) Sphagnum                                       (i) Moss

Question 12

Describe the important characteristics of gymnosperms.

Accepted 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-fixing cyanobacteria.4. The stem can be branched (as in Pinus and Cedrus) or unbranched (as in Cycas).5. The leaves can be simple (as in Pinus) or compound (pinnate in Cycas). The leaves are needle-like, with a thick cuticle and sunken stomata. These help in preventing water loss.6. Gymnosperms are heterosporous. They bear two kinds of spores – microspores and megaspores.7. Flowers are absent. The microsporophylls and megasporophylls are arranged to form compact male and female cones.8. Pollination occurs mostly through wind and pollen grains reach the pollen chamber of the ovule through the micropyle.9. The male and female gametophytes are dependent on the sporophyte.10. The seeds contain haploid endosperms and remain uncovered.

Chapter 3 : Plant Kingdom