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NCERT Solutions for class 12 Biology Chapter 2
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Chapter 2: Sexual Reproduction in Flowering Plants
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Important Terms on Chapter 2
- Autogamy: When pollen grains of a flower are transferred from anther to stigma of the same flower.
- Coleorhiza: A protective sheath of radicle in monocot seed.
- Coleoptile: A protective sheath of plumule in monocot seed.
- Nucellus: Multicellular tissue in the centre of ovule in which embryo sac is present.
- Viability of Seed: Ability of seed to retain the power of germination.
Sporopollenin is one of the most resistant organic substance. It is not affected by high temperature, strong acids or alkali. No enzyme can degrade it.
- Pollen Products: Pollen grains are rich in carbohydrates, proteins and unsaturated fats. Their consumption is believed to increase performance of athlete and horses. They are used in the form of tablets and syrups.
- Pollen Viability: Pollens of wheat and rice remain viable for 30 minutes. Pollens of same other plants may remain viable for several months. Pollens can be cryopreserved in liquid nitrogen (-196°C) in pollen banks.
- Dicot Embryo: A typical dicot embryo consist of an embryonal axis and two cotyledons. The portion of embryonal axis above the level of cotyledons is the epicotyl and the portion below the level of cotyledons is hypocotyl.
- Monocot Embryo: Monocot (Rice, Maize etc.) has one cotyledon called Scutellum. The embryonal axis has the radicle and root cap enclosed by a sheath called Coleorrhiza. The upper end (epicotyle) has plumule which is covered by hollow foliar structure called the coleoptile.
- Apomixis: Apomixis is a form of asexual repduction that mimics sexual reproduction where seeds are formed without fertilisation.
- Give the scientific name of a plant with came to India as a contaminant with imported wheat and causes pollen allergy.
- Why are pollen grains produced in enormous quantity in maize?
- In some species of Asteraceae and grasses, seed are formed without fusion of gametes. Mention the scientific term for such of reproduction.
- If the diploid number of chromosomes in an angiospermic plant is 16. Mention number of chromosomes in the endosperm and antipodal cell.
- Parthenium hysterophorus (carrot grass)
- To ensure pollination because Maize is pollinated by wind.
- Chromosomes in endosperm and 8 chromosomes in antipodal cells.
Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
Arrange the following terms in the correct developmental sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
Sporogenous tissue – pollen mother cell – microspore tetrad – Pollen grain – male gamete
During the development of microsporangium, each cell of the sporogenous tissue acts as a pollen mother cell and gives rise to a microspore tetrad, containing four haploid microspores by the process of meiosis (microsporogenesis). As the anther matures, these microspores dissociate and develop into pollen grains. The pollen grains mature and give rise to male gametes.
What is meant by monosporic development of female gametophyte?
What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Chasmogamous flowers have exposed anthers and stigmata similar to the flowers of other species.
Cross-pollination cannot occur in cleistogamous flowers. This is because cleistogamous flowers never open at all. Also, the anther and the stigma lie close to each other in these flowers. Hence, only self-pollination is possible in these flowers.
Mention two strategies evolved to prevent self-pollination in flowers.
In certain plants, the stigma of the flower has the capability to prevent the germination of pollen grains and hence, prevent the growth of the pollen tube. It is a genetic mechanism to prevent self-pollination called self- incompatibility. Incompatibility may be between individuals of the same species or between individuals of different species. Thus, incompatibility prevents breeding.
In some plants, the gynoecium matures before the androecium or vice-versa. This phenomenon is known as protogyny or protandry respectively. This prevents the pollen from coming in contact with the stigma of the same flower.
What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
The plants which exhibit this phenomenon have the ability to prevent germination of pollen grains and thus, prevent the growth of the pollen tube on the stigma of the flower. This prevents the fusion of the gametes along with the development of the embryo. As a result, no seed formation takes place.
What is bagging technique? How is it useful in a plant breeding programme?
This technique is an important part of the plant breeding programme as it ensures that pollen grains of only desirable plants are used for fertilization of the stigma to develop the desired plant variety.