Class 11th BIOLOGY Solution Chapter 3




NCERT Solutions for Class 12th Maths

Chapter 3 PLANT KINGDOM  


Question 1: What is the basis of classification of algae?
Answer Algae are classified 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 flagella 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 III – 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

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?
soln.All of these plants show life cycle with one gametophytic (n) generation and one sporophytic (2n) generation. Reduction division or meiosis that produces haploid (n) cells from diploid cells (2n) is necessary in their life cycles to restore gametophyte generation after sporophytic generation. It occurs in different body structures according to the basic body design of these groups. Reduction division in a liverwort and moss takes place at the end of the sporophytic generation, where haploid spores are formed by reduction division of spore mother cell inside capsule. Spores germinate to produce dominant gametophytic generation. Reduction division in fern takes place at the end of the dominant sporophytic generation inside the sporangium from spore mother cell by reduction division. Spores may be of one type (homospory) or of two types (heterospory).
Reduction division in gymnosperms takes place at the end of dominant sporophytic generation. Megaspore and microspores are produced by the reduction division of diploid megaspore mother cell and diploid microspore mother cell respectively, inside megasporangium and microsporangium. Reduction division in angiosperms takes place at the end of dominant sporophytic generation. The haploid pollen grain or microspore and the haploid egg cell are produced by the reduction division of diploid (microspore) mother cell and diploid megaspore mother cell respectively. Microsporic division occurs inside anther and megasporic division occurs inside gynoecium (ovary).
Question 3: Name three groups of plants that bear archegonia. Briefly 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.
NCERT Solutions Class 11th Biology Chapter 3 Plant Kingdom
4.Mentiontheploidyofthefollowingrprotonemal cell of a moss; primary endosperm nucleus in dicot, leaf cell of a moss; prothallus cell of a fern; gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.
soln. 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.

Question 5: 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-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 toothpastes. It is obtained from the red algae.
(c) Medicines: Many red algae such as Corallina are used in treating worm infections.
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.
6.Both gymnosperms and angiosperms bear seeds, then why are they classified separately?
soln.’Gymnosperms and angiosperms both bear seeds but they are classified separately because gymnosperms are a group of plants in which the ovules are freely exposed on open megasporophylls, whereas in angiosperms the seeds or ovules are enclosed within ovary which later forms the fruit.
Question 7: What is heterospory? Briefly comment on its significance. 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 first in pteridophytes such as Selaginella and Salvinia


8.Explain briefly thefollowing terms with suitable examples.
(i) Protonema (ii) Antheridium
(iii)Archegonium (iv) Diplontic (v) Sporophyll (vi) Isogamy
soln. (i) Protonema : It is the first, usually branched, green and filamentous structure produced by a germinating moss or fern spore. The protonema of mosses bears buds that develop into the gametophyte plant. In fern the protonema becomes the prothallus.
(ii)Antheridium : The male sex organ of cryptogams (algae, fungi, bryophytes and
pteridophytes) is known as antheridium. It produces the male gametes or anthero- zoids. It may consist of a single cell or it may have a wall that is made up of one or several layers forming a sterile jacket around the developing gametes.
(iii)Archegonium : The multicellular flask shaped female sex organ of bryophytes, pteridophytes and many gymnosperms is known as archegonium. Its dialated base called the venter contains the female gamete or egg or oosphere. The cells of the narrow neck of archegonium liquify to allow the male gametes to swim towards the oosphere.
(iv)Diplontic : It is the kind of life cycle in which the diploid sporophyte is dominant and this diploid phase is photosynthetic. The gametophytic phase is represented either by gametes only, that are formed through meiosis or by a highly reduced few celled gametophyte. E.g., all seed-bearing plants (gymnosperms and angiosperms).
(v) Sporophyll : It is a type of leaf bearing sporangia. In ferns, the sporophylls are the normal foliage leaves, but in other plants the sporophylls are modified and arise in specialised structure such as the strobili of club-moss, gymnosperms and the flower of angiosperms. In most plants sporophylls are of two types – microsporophylls and megasporophylls.
(vi)Isogamy: It is a type of sexual reproduction where fusion takes place between two identical gametes. The gametes are similar in size and structure and they show equal motility during sexual reproduction, e.g., Spirogyra (algae).
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
Answer
Sr. No.Red algaeBrown algae
1.Red algae are grouped under theclass Rhodophyceae.Brown algae are grouped underthe class Phaeophyceae.
2.They contain floridean starch asstored food.They contain mannitol or laminarin as stored food.
3.They contain the photosyntheticpigments  chlorophylls  a  and  d, and phycoerythrin.They contain the photosyntheticpigments  chlorophylls  a  and  c, and fucoxanthin.
4.Their cell walls are composed ofcellulose, pectin, and phycocolloids.Their cell walls are composed ofcellulose and algin.
5.Flagella are absentTwo flagella are present

LiverwortsMoss
1.They have unicellular rhizoids.1.They have multicellular rhizoids.
2.Scales are present very often2.Scales are absent
3.They  are  generally  thalloid,With dichotomous branching.3.They are  foliage, with  lateralbranching.
4.Gemma cups are present4.Gemma cups are absent
5.Sporophyte has very little photosynthetic tissue5.Sporophyte has abundant photosynthetic tissue

  Homosporous pteridophytes  Heterosporous pteridophytes
1.They bear spores that are of the same type.1. They bear two kinds of spores – microspores and megaspores.
2. They produce bisexual gametophytes.2. They produce unisexual gametophytes.
SyngamyTriple 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.
10.How would you distinguish monocots from dicots?
Soln. Differences between monocots and dicots are as follows :
ncert-solutions-for-class-11-biology-plant-kingdom-5
11.Match the following (Column I with Column II).
Column I                                                             Column II
(a)Chlamydomonas                                       (i)Moss
(b)Cycas                                                             (ii)Pteridophyte
(c) Selagmella                                                 (iii)Algae
(d) Sphagnum                                                 (iv)Gymnosperm
Soln.
Chlamydomonas     –   Algae
Cycas                         –    Gymnosperm
Selayinella                –    Pteridophyte
Sphagnum                –    Moss

Question 12: 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-fixing cyanobacteria.



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