question_answer

(i) What is an endosperm?

(ii) Endosperm development preceedes embryo development. Explain.

(iii) What is the fate of endosperm in angiosperms?

Or

(i) Geitonogamy is functionally a cross-pollination, but genetically similar to autogamy. Explain.

(ii) Why do flowering plants need to develop outbreeding devices? Explain any there such devices developed by flowering plants.

Answer:

(i) Endosperm is a food laden tissue which is meant for nourishing the embryo in seed plants. In gymnosperms, it represents the female gametophyte. In angiosperms, the endosperm is a special tissue which is formed as a result of triple fusion of a male gamete with diploid secondary nucleus of the central cell.

(ii) The embryo development starts only after a certain amount of endosperm is formed. It is an adaptation for assured nutrition to the developing embryo. Therefore, endosperm development preceedes embryo development.

(iii) Fate of endosperm During its growth, the endosperm crushes the nucellus. It is inturn eaten by growing embryo. The endosperm may persist in the seed and in this case, the latter is called endospermic or albuminous (e.g. castor, cereals, coconut). In others, the endosperm is completely absorbed by the growing embryo and the food reserve gets stored in the cotyledons. Such seeds are called non-endospermic or exalbuminous, e.g. pea, bean, sunflower.

Or

(i) Transfer of pollen grains from the anther to stigma of another flower of the same plant is called geitonogamy. It is functionally cross-pollination as it involves a pollinating agent, but genetically similar to autogamy because, the pollen grains come from the same plant (genetically same parent).

(ii) Continued self-pollination results in inbreeding depression because majority of flowering plants produce hermaphrodite flowers and pollen grains generally came in contact with the stigma of same flower. To discourage this, flowering plants developed many devices. Some of them are as follows

(a) Pollen grains release and stigma receptivity are not synchronised, either the anther matures first or the stigma.

(b) Anther and stigma are placed at different position, so that the pollens cannot come in contact with the stigma of same flower.

(c) A genetic mechanism called self-incompatibility, prevents self-pollen from fertilising the ovules either by inhibiting pollen germination or by retarding the growth of pollen-tube in the pistil.

(d) By producing unisexual flowers.