What is the function of the two male gametes produced by each pollen grain in angiosperms.
One male gamete unites with egg forming embryo. This process is called fertilisation or syngamy.
Another male gamete unite with two polar nuclei resulting in the formation of endosperm triple fusion.
List three strategies that a bisexual chasmogamous flower can evolve to prevent self-pollination (autogamy).
A bisexual chasmogamous flower can evolve the following (three) strategies to prevent self-pollination (autogamy).
(a) Dichogamy In this mechanism, pollen release and stigma receptivity are not synchronised. In sunflower, the pollen is released before the stigma becomes receptive (protandry). In Datura, Solanum, the stigma becomes receptive much before the release of pollen (protogyny) leads to cross-pollination.
(b) Herkogamy The male and female sex organs are placed at different positions or in different directions is called Herkogamy. In these plants, the pollen cannot came in contact with the stigma of the same flower. It has undergone cross pollination, e.g., Hibiscus, Gloriosa.
(c) Self-sterility It is a genetic mechanism which prevents the self-pollen from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil, e.g., Abotilon.
Given below are the events that are observed in an artificial hybridisation programme. Arrange them in the correct sequential order in which they are followed in the hybridisation programme (a) Re-bagging (b) Selection of parents (c) Bagging (d) Dusting the pollen on stigma (e) Emasculation (f) Collection of pollen from male parent.
The correct sequential order of artificial hybridisatian is as following
(a) Selection of parents.
(b) Emasculation (removal of anthers from the flower bud before the anther dehisces).
(c) Bagging (process to cover the emasculated flower with a bag made up of butter paper).
(d) Collection of pollen from other male plant.
(e) Dusting of pollen on stigma.
(f) Re-bagging
$$ \text { Vivipary automatically limits the number of offsprings in a litter. How? } $$
Vivipary is defined as the seed germination, while the fruit is still attached to the mother plant. Plants which grow in marshy places are called Mangroves. In these plants when seeds fall on marshy places, they cannot germinate, because of high salinity and more water conditions.
So, in those plants, seeds germinate when they are still attached to the mother plant. Litter is the off spring at one birth of animal usually 3-8 in number.
Vivipary automatically limits the number of offspring in litter due to the reason that limited number of egg or ovum are produced and fertilised during reproductive cycle of female.
Does self-incompatibility impose any restrictions on autogamy? Give reasons and suggest the method of pollination in such plants.
Self-incompatibility imposes restrictions on autogamy. The season far this may be as Majority of flowering plants produce hermaphrodite flowers and when pollens grains comes in contact with the stigma of the same flower to continue self-pollination.
Such type of continued self-pollination result in inbreeding depression. That's why flowering plants have developed many devices to discourage self-pollination and to encourage cross-pollination. One of the major way to prevent self-pollination is self-sterility.
Self-sterility in some bisexual flowers, if the pollen grains fall on the stigma of the same flower, germination does not occur. But the same pollen grains germinate when they fall on the stigma of other flowers of the same species. It is a genetic mechanism to prevent self pollination.