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Sexual Reproduction In Flowering Plants

Question
CBSEENBI12001274
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What are the various adaptations in angiospermic flowers which favour cross-pollination ? 
Or
Explain adaptations by which autogamy is prevented in flowering plants.

Solution
In many plants there are adaptations which completely or partially prevent self-pollination or autogamy and encourage cross-pollination.

1. Unisexuality. The flowers are unisexual i.e. stamens and carpels occur in different flowers. They may be present on same plant e.g., in maize or on different plants e.g. in Papaya. The first condition called monoecious and second is called dioecious. 

2. Dichogamy. When stamens and carpels of bisexual flowers mature at different times, it is called as dichogamy. If stamens mature first it is called protandrous condition, or if carpels mature first it is called protogynous condition. Dichogamy prevents self-pollination and ensure cross-pollination.

3. Self sterility. In orchids, pollen grains of one flower do not geminate on stigma of the same flower. This is called self-sterility. The pollen grains germinates on the stigma of some other plant and thus ensure cross-pollination.

4. In some species the anther and stigma are placed at different levels so that the pollen does not come in contact with the stigma of the same flower.

5. Plants bears flowers which have characteristics to favour cross pollination  like attractive color, smell, may produce nectar. be very light and feathery pollen grains, sticky stigma etc .

Some More Questions From Sexual Reproduction in flowering Plants Chapter

The female gametophyte of a typical dicot at the time of fertilization is:

Development of embryo  from any cell of nucellus is called :

Parthenocarpic fruit is :

The entry of pollen tube into embryo sac through the integuments is termed as :

512 microspores will be formed following meiosis of how many microspore mother cells.

Pollination by water occurs in :

In ................... flowers, the thalamus grows upwards completely enclosing the ovary, and the stamens, petals and sepals are borne above the ovary.

In Calotropis, all the microspores of anther lobe remain united to form

Albuminous seeds store reserve food materials in ....................

Transfer of pollen grains from the anther to the stigma of another flower of same plant is called..............................

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