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Sexual Reproduction in Flowering Plants — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYSexual Reproduction in Flowering Plants4 Marks
Question
  1. State one difference and one similarity between geitonogamy and xenogamy.
  2. Explain any three devices developed in flowering plants to discourage self pollination and encourage cross-pollination.
✓

Answer

  1. Difference between geitonogamy and xenogamy:
S. No.
Geitonogamy
Xenogamy
1.
Transfer of pollen grains from the anther to the stigma of another flower of the same plant. 
Transfer of pollen grains from the anther to the stigma of the different plant.
2.
Does not provide an opportunity for gametic recombination. 
Provides an opportunity for gametic recombination.

Similarity : Both help in pollination by transfer of pollen grains to the stigma.

 

  1. Continued self-pollination leads to interbreeding depression so in order to discourage self-pollination and to encourage cross-pollination, many flowering plants have developed many devices.

Outbreeding devices in plants:

  • In some species, the pollen release and stigma receptivity are not synchronised. Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much more before the release of pollen.
  • In some other species, the anther and the stigma are placed at different positions so that the pollen can’t come in contact with the stigma of the same flower.
  • Some species have self-incompatibility which is a genetic mechanism. When the pollen from the same flower or the other flowers of the same plant falls on the stigma, this mechanism inhibits pollen germination or pollen tube growth in the pistil.

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