Importance of day length in flowering of plants was first shown in 

  • Lemna

  • tobacco

  • Cotton 

  • Cotton 


B.

tobacco

The phenomenon of photoperiodism was first discovered by Garner and Allard (1920, a mammoth variety of tobacco could be made to flower only by reducing the light hours with artificial darkening. On the basis of photoperiodic response to flowering, plants (tobacco), long day plant (eg, wheat, hanbane), short - long day plant (eg Campanula), long short day plants, (eg, wild kidney bean) and day neutral plants (eg, cotton).

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Unisexuality of flowers prevents

  • autogamy, but not geitonogamy

  • Both geitonogamy and xenogamy

  • geitonogamy, but not xenogamy

  • geitonogamy, but not xenogamy


A.

autogamy, but not geitonogamy

The transfer of pollen from the anther to stigma is called pollination. Autogamy also called self-pollination involves the transfer of pollen grains on one flower to the stigma of the same flower. Self-pollination occurs only in bisexual or hermaphrodite flowers.

Geitonogamy involves the transfer of pollen grains from a male flower to the stigma of the female flower of the same plant. Thus, geitonogamy operates only in monoecious plants ie, the plants having male and female flowers on different places. 

Allogamy or xenogamy knew as cross-pollination involves the transfer of pollen grains of the male flower to the stigma of the gentically different female flower. It takes place via, various agencies like wind, water, insects etc.

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Which one of the flowing pairs of plants structures has haploid number of chromosomes?

  • Megaspore mother cell and antipodal cells

  • Egg cell and antipodal cells

  • Nucellus and antipodal cells

  • Nucellus and antipodal cells


B.

Egg cell and antipodal cells

In angiosperms, a single diploid megaspore mother cell matures within the ovule. Through meiosis, it gives rise to four megaspores (haploid). In most plant, only one of these megaspore divides three times by mitosis and produces eight haploid nuclei enclosed with a 7 celled embryo sac. One nucleus is located near the opening of embryo space in the middle of embryo sac and is called polar nuclei, two nuclei are contained in cells called antipodals, located at the end of the embryo sac, opposite the egg cell.

Nucellus is centrally located mass of thin-walled parenchymatous cells covered by integuments in ovule.

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What does the filiform apparatus do at the entrance into ovule?

  • It helps in the entry of pollen tube into a synergid

  • It prevents entry of more than one pollen tube into the embryo sac

  • It brings about opening of the pollen tube

  • It brings about opening of the pollen tube


A.

It helps in the entry of pollen tube into a synergid

In most cases, the mature embryo sac contains 7-cells and nuclei. The cells are arranged egg apparatus (two synergid cell and one egg cell,) a central cell with two nuclei and antipodal cells ( 3 in number). The synergid cells occur laterally to the egg cell. These cells are characterised by finger- like projections called filiform apparatus towards the micropylar end. Fill form apparatus is formed due to invaginations of cell wall into the protoplasm and is made up of pectocellulosic fibres evolved in the non-cellulosic sheath. Secretion of chemotactic substances for the attraction of pollen tube during fertilisation is the function of synergies. One synergid becomes degenerate during pollen entry into the embryo sac and thus, provides a way for the entry of pollen tube into the embryo sac.

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Male gametes in angiosperms are formed by the division of

  • microspore

  • generative cell

  • vegetative cell

  • vegetative cell


B.

generative cell

Before pollination the pollen grain cytoplasm divides in generative cell and vegetative cell. The generative cell divides to form two male gametes.

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