a) Write the structure and functions of placenta.
b) What are the changes that occur in a flower after fertilization.

Explanation

a) Placenta is a disc which is embedded in the uterine wall. It contains villi on the embryo.s side of the tissue. On the mother.s side are blood spacer, which surround the villi. This provides large surface area for glucose and oxygen to pass from mother to the embryo. The waste generated in the embryo is removed by transferring them into the mother.s blood through the placenta.
b) Pollen grain develops pollen tube containing two male gametes, travels from stigma to style to reach the ovule for fertilization to take place. Male and female gametes fuse in the ovule and after fertilization. zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is gradually converted into a seed. The ovary grows rapidly and ripens to form a fruit. Meanwhile, the petals. sepals, stamens, style and stigma may shrivel and fall off. The seed contains a seed coal an embryo with plumule - future shoot. radicle. future root and one or two catyledons which supply food to the germinating seed at a later stage.