31.

Give reasons why:
a. Most zygotes in angiosperms divide only after certain amount of endosperm is formed.

b. Groundnut seeds are exalbuminous and castor seeds are albuminous.

c. Micropyle remains as a small pore in the seed coat of a seed.

d. Integuments of an ovule harden and the water content is highly reduced, as the seed matures.

e. Apple and cashew are not called true fruits.

a. Development of embryo depends upon the amount of endosperm present in the nucleus, as the embryo obtain its nutrition from the endosperm only. The cells of the endosperm tissue are filled with reserve food materials and provide nourishment to the developing embryo.

b. Utilization of the endosperm vary among plants, in some plants endosperm, gets exhausted or used up and produce exalbuminous seeds e.g groundnut.
In plants like castor some part of the endosperm persist in the seeds and are used during seed germination, these seeds are termed as albuminous

c. Seeds are covered by a hard covering called as integument, except at the top part of seed called as micropyle. Mycropyle helps in the entry of O₂ and H₂O during seed germination. Pollen tube enters the ovary through the micropyle. 

d. Maturation of seed is preceded by reduction in water content and increase hardening of integuments. Reduced content of water makes the seed metabolically slow and dry. Then embryo enters into dormancy stage. When seeds are subjected to adequate moisture, oxygen and suitable temperature they start to grow.

e. Maturation of ovules into seed and development of ovary into fruit occur simultaneously. When fruit develops from thalamus rather than from ovary are termed as false fruit.