Class-XI-Biology Plant Kingdom

Class-XI-BiologyPlant KingdomCBSE NCERT Solutions for Class 11 Biology Chapter 03Back of Chapter Questions1. What is the basis of classification of algae?Solution:Algae are classified into three main classes – Chlorophyceae, Phaeophyceae, andRhodophyceae based on the following factors:(a) Major photosynthetic pigment present(b) Cell wall composition(c) Form of stored food(d) Number of flagella and position of the eCommon nameGreen algaeBrown algaeRed algaeMajor pigmentsChlorophyll a and bChlorophylls a and c, and Chlorophylls a and b,Stored foodCellStarchwall Cellulosefucoxanthinand phycoerythrinMannitol and laminarinFloridean starchCellulose and alginCellulose, pectin, andpolysulphate esterscompositionFlagella number 28; equal and apical2; unequal and lateralAbsentand position(Note: Cyanophyceae - Blue Algae, is another class of algae which containsPhycocyanin pigments.)1Practice more on Plant Kingdomwww.embibe.com

Class-XI-BiologyPlant Kingdom2. When and where does reduction division take place in the life cycle of a liverwort, amoss, a fern, a gymnosperm and an angiosperm?Solution:(Note: Illustrations are not required, but they are put here for better understandingof the concepts)Liverwort – Their main plant-body is haploid (gametophytic). It has female and male sex organswhich produce gametes. These gametes fuse to form a zygote. The zygote develops on themother spores to form a sporophyte. The sporophyte is differentiated into the foot, seta, andcapsule. Many haploid spores are formed as a result of the reduction division (meiosis) takingplace in the capsule of this sporophyte.Lifecycle of Liverwort2Practice more on Plant Kingdomwww.embibe.com

Class-XI-BiologyPlant KingdomMoss – In mosses, the primary protonema that developed in the first stage develops into thesecondary protonema. Both the stages are haploid or gametophytic. The secondary protonemahas sex organs and produces gametes. The gametes fuse to form a zygote. The zygote developsinto a sporophyte. Many haploid spores are formed as a result of the reduction division (meiosis)taking place in the capsule of this sporophyte.Lifecycle of MossFern – Their main plant-body is sporophytic. Their leaves are known as sporophylls, and theybear the sporangia. Reduction division takes place in these sporangia present in the ventralsurface of the leaf, thereby producing many spores.3Practice more on Plant Kingdomwww.embibe.com

Class-XI-BiologyPlant KingdomLifecycle of FernGymnosperm – Their main plant-body is sporophytic. They have two types of leaves –megasporophylls and microsporophylls. Reduction division takes place in the megasporangiapresent on the megasporophylls (producing megaspores) and the microsporangia present on themicrosporophylls (producing pollen grains). Hence, meiosis takes place in antheridium andovary for the formation of pollen grains and ovules, respectively.4Practice more on Plant Kingdomwww.embibe.com

Class-XI-BiologyPlant KingdomLifecycle of GymnospermAngiosperm – Their main plant-body is sporophytic and they bear flowers. Their male sexorgan in flower is the stamen, and the female sex organ is the pistil in flower. Reduction divisiontakes place in the anthers of the stamen (producing haploid pollen grains) and in the ovaryof the pistil (producing eggs).5Practice more on Plant Kingdomwww.embibe.com

Class-XI-BiologyPlant KingdomLifecycle of Angiosperm3. Name three groups of plants that bear archegonia. Briefly describe the life cycle ofany one of them.Solution:Archegonium are the female sex organs which produce the female gametes or eggs. Theyare present in the life cycles of bryophytes, pteridophytes, and gymnosperms.The life cycle of a fern (Dryopteris)-Dryopteris are common ferns with pinnate-compound leaves.6Practice more on Plant Kingdomwww.embibe.com

Class-XI-BiologyPlant Kingdom-Their main plant-body is sporophytic.-The sporangia are borne on the ventral surfaces of mature leaves.-Each sporangium has spore mother cells, and they undergo meiosis to producehaploid spores.-Upon maturation, these spores dehisce and germinate to give rise to a heart-shapedgametophyte called prothallus.-The prothallus has both male and female sex organs called antheridia andarchegonia, respectively.-The antheridia produce sperms which swim in the water to reach to the archegonia.The archegonia produce the egg.-A zygote is formed as a result of fertilisation. The zygote matures into an embryo,which in turn develops into a new sporophyte. The young plant comes out of thearchegonium of the parent gametophyte.Figure: The life cycle of a fern7Practice more on Plant Kingdomwww.embibe.com

Class-XI-BiologyPlant Kingdom4. Mention the ploidy of the following: protonemal cell of a moss; primary endospermnucleus in dicot, leaf cell of a moss; prothallus cell of a fern; gemma cell inMarchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.Solution:-protonema 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: Diploid5. Write a note on economic importance of algae and gymnosperms.Solution:Economic importance of Algae:a. Agar is obtained commercially from Gelidium and Gracilaria, which is widely used inthe preparation of jellies, puddings, cream, etc. Also, agarose, which is obtained fromagar, is widely used in biotechnology labs for making gels to run DNA samples.b. Carrageenin is used as an emulsifier in chocolates, paints, and toothpaste. It is obtainedfrom the red algae.c. Some of the marine algae such as Porphyra, Sargassum, and Laminaria are edible.Chlorella and Spirulina are rich in proteins. Hence, they are used as food supplements.8Practice more on Plant Kingdomwww.embibe.com

Class-XI-BiologyPlant Kingdomd. Antibiotic chlorellin is extracted out from Chlorella. Red algae - Corallina is used intreating worm infections.Economic importance of Gymnosperm:a. Conifers provide an enormous amount of softwood for construction, plywood, paperindustry etc.b. Seeds of Pinus (Chilgoza) are edible.c. Ephedrine drug is obtained from Ephredra used in asthma and bronchitis. An anticancerdrug Taxol is obtained from Taxus.d. 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. Sawdust ofconifers is used in making linoleum and plastics.6. Both gymnosperms and angiosperms bear seeds, then why are they classifiedseparately?-Solution:- The seeds of the gymnosperm are naked, whereas a membrane covers the seeds ofthe angiosperm. Hence, both gymnosperms and angiosperms are classifiedseparately.-The other difference between angiosperms and gymnosperms is that the diversityof angiosperm is greater than the gymnosperm. The higher diversity indicated theangiosperms are adaptive to terrestrial ecosystems.9Practice more on Plant Kingdomwww.embibe.com

Class-XI-BiologyPlant Kingdom7. What is heterospory? Briefly comment on its significance. Give two examples.Solution:-Heterospory is the presence of two kinds of spores on the same plant.-These spores differ in size. The smaller one is known as microspore (germinates toform the male gametophyte-pollen grain), and the larger one is known as megaspore(germinates to form the female gametophyte-egg). The male gametophyte releasesthe pollens, and these reach the female gametophyte to fuse with the egg. Inside thefemale gametophyte, fertilisation results in the development of the zygote.-This retention and germination of the megaspore within the megasporangiumensure proper development of the zygote into a young embryo. The evolution ofthe seed habit is related to the retention of the megaspore. Heterospory is thusconsidered an important step in evolution as it is a precursor to the seed habit. Theheterospory is the first step of evolution of seed development in gymnosperms andangiosperms.-Heterospory evolved first in pteridophytes such as Selaginella and Salvinia.8. Explain briefly the following terms with suitable examples:(i) protonema, (ii) antheridium, (iii) archegonium, (iv) diplontic, (v) sporophyll, (vi)isogamySolution:(i)Protonema: The predominant-first stage of the life cycle of a moss is theprotonema stage, which develops directly from a spore. It is a creeping, green,branched and frequently filamentous stage.Example: Sphagnum.10Practice more on Plant Kingdomwww.embibe.com

Class-XI-Biology(ii)Plant KingdomAntheridium: It is the male sex organ of bryophytes and pteridophytes, whichis surrounded by a jacket of sterile cells. They produce biflagellateantherozoids.Example: Selaginella.(iii)Archegonium: It is the female sex organ of bryophytes, pteridophytes, andgymnosperms. They produce biflagellate antherozoids.Example: Cycas.(iv)Diplontic: It represents the gametophytic phase during the lifecycle ofangiosperm and gymnosperm (seed-bearing plants). In this, the diploidsporophyte is dominant. If the gametophytic phase is represented by the singleto the few-celled haploid gametophyte, such kind of lifecycle is termed asdiplontic.Example: Pinus.(v)Sporophyll: The main plant body of the pteridophytes is sporophytic. Thesporophytes bear sporangia that are subtended by leaf-like appendages calledsporophylls.Example: Nephrolepis.(vi)Isogamy: It is a mode of reproduction in which there is a union or fusion ofgametes of the same size and structure.Example: Spirogyra.9. Differentiate between the following:(i) red algae and brown algae(ii) liverworts and moss(iii) homosporous and heterosporous pteridophyte11Practice more on Plant Kingdomwww.embibe.com

Class-XI-BiologyPlant Kingdom(iv) syngamy and triple fusionSolution:(i) red algae and brown algaeCommon nameBrown algaeRed algaeClassPhaeophyceaeRhodophyceaeMajor pigmentsChlorophylls a and c, and Chlorophylls a and b,Stored foodCellfucoxanthinand phycoerythrinMannitol and laminarinFloridean starchwall Cellulose and alginCellulose, pectin, andcompositionpolysulphate estersFlagella number 2; unequal and lateralAbsentand position(ii) liverworts and mossLiverwortsThey have unicellular rhizoids.Scales are present very often.They are generally thalloid, with dichotomousbranching.Gemma cups are present.Sporophyte has very little photosynthetic tissue.Thallus is dorsoventrally flattened and lobedliver like.MossThey have multicellular rhizoids.Scales are absent.They are foliage, with lateral branching.Gemma cups are absent.Sporophyte has abundant photosynthetic tissue.Thallus is leafy and radially symmetrical.(iii) homosporous and heterosporous pteridophyteHomosporous pteridophyteThey bear spores that are of the same type.They produce bisexual gametophytes.Heterosporous pteridophyteThey bear two kinds of spores – smallmicrospores and large megaspores.They produce unisexual gametophytes.12Practice more on Plant Kingdomwww.embibe.com