question_answer

Draw a labelled diagram of the sectional view of a mature pollen grain in angiosperms. Explain the functions of its different parts.

OR

(i) What is the role of cervix of the human female system in reproduction?

(ii) Distinguish between spermatogenesis and oogenesis.

Answer:

Functions of the parts of Pollen grains: A mature pollen grain has two layered wall-the outer exine and the inner intine. The wall encloses a large vegetative cell containing vegetative nucleus and a lenticular generative cell.
Their functions are as follows:
Exine: The outer thick exine layer is made up of sporopollenin which is resistant to physical and biological decomposition. It provides protection during the hazardous journey of pollen from anther to the stigma. There are one or many germpores on the pollen surface which are directly or indirectly associated with its germination.
Intine: The intine is pecto-cellulosic in nature. It is associated with the formation of pollen tube.
Vegetative cell: The vegetative cell is large and contains abundant food reserve. It has a large vegetative nucleus. The function of vegetative cell is to provide the medium for the movement of male gametes in pollen tube.
Generative cell: The generative cell cytoplasm is highly reduced but it contains the usual cell organelles. It divides mitotically to produce two functional male gametes.
OR
(i) Cervix helps in regulating the passage of sperms into the uterus and forms the birth canal to facilitate parturition.
(ii)
S. No.	Spermatogenesis	Oogenesis
(a)	It is the process of formation of haploid spermatozoa from diploid male germ cells of the testes.	It is the process of formation of haploid ova from the gamete mother cells (oogonia) in the ovary.
(b)	It occeurs in testes.	It occurs in ovaries.
(c)	Spermatogoina chamges to primary	Oogonia changes to primary oocyte.
(d)	A primary spermatocyte divides to from two secondary spermatocytes.	A primary oocyte divides to form one secondary oocyte and a polar body.
(e)	A secondary spermatocyte divides to from two spermatids.	A secondary oocyte divides to from one ovum and a polar body.
(f)	No polar body is formed.	Polar bodies are formed.
(g)	Four spermatozoa are produces.	One ovum/egg is produced.