12th new syllabus Reproduction in plants Notes HSC & CBSC board
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July 30, 2020
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12th new syllabus Reproduction in plants Notes HSC & CBSC board
1. The ability of living organisms to give rise to young ones of their own kind is called
2. . In angiosperms , there are two major modes of reproduction , viz.asexual IN A NUTSHELL reproduction and sexual
. Asexual reproduction :
Production of offspring without involving the fusion of gametes is called asexual reproduction . Its also called apomixis as it occurs without the mixing of the genetic material .
• Asexual reproduction is more common than sexual reproduction in lower organisms .
• Asexual reproduction in lower organisms is of four types , viz . binary fission , budding sporulation and fragmentation .
• In binary fission , the parent cell divides into two equal cells which give rise to two new individuals . Binary fission is seen in bacteria and Amoeba .
• In budding a small and unequal cell grows out from the parent cell ( bud ) which on separation matures into a new individual , e.g. yeast . Algae and fungi reproduce by spores
. • Algae produce motile spores called zoospores , e.g. Chlamydomonas while fungi produce nonmotile spores , called conidia , e.g. Penicillium . Some filamentous algae reproduce fragmentation , e.g. Spirogyra .
• Asexual reproduction is uniparental as it involves only one parent .
4. Vegetative reproduction: The reproduction which occurs with the help of vegetative organs like root , stem , leaf or bud is called vegetative reproduction or vegetative propagation .
5. Natural methods of vegetative reproduction : In natural methods of vegetative propagation a part of plant acts as a propagule which under favourable conditions grows and develops into new plant . -
by stem tubers: The stem tuber is an undergroand mudification of stenn. In thi the teminal part of the underground stem swells dae to the storae t starchy rve food to form a tubent A stem tuber bears a number of notches on its surface called eyes Thr eye la actunly a nie bearing one or more amall axillary buds and reduced scaly lenves. Cne of the xillary bada frum an eye sprouts and gives rise to a new pslant. The pirces of tuber with at lest one ye are yrown for commercial production, e.AT. potato
By runner : The runner is a slender and prostrate sub-aerial tranch which ereeps bortecetally on the ground and becomes rooted at the ndes. Shoots which are prodticed from the upper side of the nodes, get detached from the parent plant and grow as independent plants Plants such a Cynodon, Fraguria and Oxalis produce runners for vegetative propapation.
By leaf buds : In plants such as Bryuphyllum. Kalanchoe tanid Bgonio, vertative reproduction occurs with the help of leaf buds In Bryophyllum, the leaf bears buds in its notchnd, mArgiTs. These buds sprout on the leaf to form leafy shoots and adventitions roots which on separatiun fall on the wet soil and develop into new plants. In Eegonta, the leaf buds are pproduoed on the surface of the leaves
6. Artificial methods of vegetative propagation :Cutting, grafting and budding are artificial methods of vegetative propagation developed by ugriculturists and hortieuiturists
(1) Cuttings : Cuttings are small pieces of plant parts like roots, stems or leaves which when placed in moist soil develop into new plants. All types of ornamental plants and Hotne types of fruit plants are propagated from cuttings.
(2) Grafting : Grafting is an artificial method of vegetative propagation in which the parts of two different plants are joined in such a way, that they unite with each other and continue their growth as one plant. In grafting, the rooted plant is called the stock while the other which is grafted on the stock is
(3) Budding : Budding is a type of grafting in, which a single bud with a small portion of living tissue with bark is grafted on the stock called scion.
7. Micropropagation : To produce large number of genetically identical plants mieropropagules are used. This mode of reproduction is called micropropagation.
Sexual reproduction : Production of offspring which involves the fusion of gametes is called sexual Flower Flower is a highly specialized organ meant for sexual reproduction. Sexual roproduction in flowering plants involve the events like development of male gametophyte, development of female gametophyte,
Anther: The stamen which is the male reproductive oruan of a flower consists of two anther The anther s connected to the filament. 11
. Pollen itrain : The poilen rain is a spherical haploid structure. It is a unicellular and tuniniele structure consisting of a double-layered wall-the outer exine and the inner intine. The esxite ay smooth or stpiny.
12. Male gametophyte : Male gametophyte is formed by the pollon grain. It is highly rduced The pollen tube with two nale gametes represents the male gametophyte. The male uametophyte highly reduced strueture.
13. Anatropous ovule : The ovule which has a bent axis and downwardly directed micropyle in call zthatropous ovule. It is the most common type of ovule in angiosEMH t
14. Female gametophyte: The embryo sar which develops within the ovule is called fe gametophyte. The female gametophyte is monosporic, endosporic, seven celled and eight noele structure.
15. Pollination : The transfer of polle grains from the anther to the stigma of a flower is C pollination. Pollination is of two types: viz, self pllination and erosS pollination.
16. Self pollination : Transfer of pollen grains from the anther to the stigma of the same flowet w dterent llower possessing the same genetic make-up is called self pollination. It occurs following three ways: D
Autogamy : The pollen grains from the anther of a flower are translerred to the stigma of same flower, e.g., bisexual flowers.
(2) Geitonogamy : Geltonogamy is the transfer of pollen grains from the anther of a flower to stigma of another flower borne by the same plant.
(3) Pollen grains are transferred from the anther of a flower produced on one plant to the stigmad flower produced on another plant possessirg the same genetic make up.
17. Cross pollination (Allogamy) : The transfer of pollen grains from the ather of a flower to stigma of another flower produced on a different plant possessing dissimilar genetie make-up h the following two types :
(1) Xenogamy: When pollen grains are transferred from the anther of a flower to the stigna another flower borne by a different plant, belonging to the same species, it is callerd xenogan e.g. papaya.
(2) Hybridization : When pollen grains are transferred from the anther of a flower to the stigmad another flower produced on a different plant belonging to a different species, it is til hybridization e.g., pollination between two species of cotton.
18. Agencies of pollination: Plants depend upon certain external carriers for pollination. Ther external carriers are called agencies of pollination or pollinating agents. The following are the main pollinating agents :
(1) Abiotic agents : Physical factors such as wind or water which help in the transfer of pal grains from the anther to the stigma are abiotic pollinating agents.
(i) Anemophily : Pollination with the help of wind is called anemophily, and the wind pollinated plants are called anemophilous plants, e.g., grasses, maize, sugar cane, etc
(ii) Hydropihily Pollination effected through the agency of water is called hydrophily. Water pollinated plants are called hydrophilous plants, eg. Hydrilla, Vallisneria, Ceratophyllum, etc.
(ii) Entomophily: Pollination effected through the agency of insects is called entomophily. The insect pollinated flowers are called entomophilous flowers e.g., rose, Cestrum, Saluta, Bougainvillea, etc.
(iv) Ornithophily : Pollination effected through the agency of birds is called ornithophily. Bird pollinated flowers are called ornithophilous. e.g., Butea, Bombax, Callistemon, Bignonia, etc.
(v) Chiropterophily Pollination effected through the agency of bats is called chiropterophily. 19. Outbreeding devices : Most of the angiosperms prefer cross pollination. To achieve cross pollination and avoid self pollination they develop outbreeding devices. Some of these devices are as follows :
(1) Dichogamy Maturation of anthers (stamens) and stigma (carpel) at different tìmes is called dichogamy. Dichogamy stands as a barrier to self pollination. It is of two types, viz. protandry and protogyny.
(i) Protandry : In some plants, for example, sunflower, the pollen grains are released much before the stigma is ready to receive the pollen grains. This condition is known as protandry.
(ii) Protogyny : In plants like Michelia, stigma matures first. As a result of this, fertilization takes place first before the pollen grains are matured.
(2) Self sterility or self incompatibility : In plants like orchids, the germination of pollen grains on the stigma of the same flower is inhibited. This is a genetic mechanism to avoid self pollination. This mechanism is known as self sterility or self incompatibility.
(3) Unisexuality : Plants in which the flowers are unisexual, the self pollination is out of question.
20. Fertilization : The union of male gamete with the female gamete is called fertilization.
21. Double fertilization : In angiosperms out of the two male gametes one unites with the female gamete and the other with the secondary nucleus. Since both the male gametes take part in fertilization and fertilization occurs twice, it is called double fertilization. nf a male gamete with the secondary
23. Parthenocarpy: • Production of fruits without fertilization is called parthenocarpy. • Parthenocarpic fruits are seedless fruits. • In banana, the fruits are parthenocarpic.
24. Apomixis: • Production of seeds without fertilization is called apomixis. • Apomixis is a form of asexual reproduction which mimics sexual reproduction. • Apomixis is seen in grasses, sunflowers and roses. • Seeds produced by apomixis are called apomictic seeds.
25. Polyembryony: In some plants, for example, Citrus species, the ovule contains many embryos This is called polyembryony.
26. Formation of fruits and seeds : • After fertilization, the ovule develops into the seed and the ovary develops into the fruit. Therefore the seed is a mature or ripened ovule while the fruit is a mature or ripened ovary. • The seeds are the most efficient propagules that are produced by the plants. • The dominance of angiosperms on the earth is due to the seeds.
27. Dormancy : The temporary suspension of growth is called dormancy. During dormancy period, the seeds do not germinate.
28. Viability : The ability of seeds to germinate after dormancy period, is called viability.
29. Dispersal : Dispersal refers to the movement of seeds or fruits to the distant places from the parent plants.
