January 27, 2014

10th Class Biology - Imp Questions for 4 Marks - Reproduction

Q: Describe the menstrual cycle in human beings.

A: The changes in the female reproductive system is known as menstrual cycle. It consists of
(1) Proliferative Phase, (2) Secretory Phase.

During proliferative phase cells present in the follicle, fallopian tube, uterus, vagina increase in number by repeated divisions.
In menstrual cycle first 12 to 14 days the follicle matures and releases the ovum on 14th day.
The second phase is known as secretory phase. During this phase the ruptured follicle is converted into corpus luteum and uterine walls are thickened.

Uterus waits for the embryo to reach uterus. After fertilization the formation of egg stops.
If this does not occur by 26th day the cells of corpus luteum and the walls of uterus are detached and are expelled along with some amount of blood.
Immediately after this, the proliferative phase once again starts.

Q: What is "tissue culture"? What are the advantages of it?

A: A cell or tissue taken from a plant cultured in suitable containers which is called tissue
culture. New plants can be obtained from the single cell or tissue.

Advantages:

(i) Desirable plants can be rapidly multiplied.
(ii) Multiplication can be done in a small space under controlled conditions.
(iii) It is possible to obtain plants that are free from pathogens, particularly viruses.
(iv) Embryos that do not develop in ovaries can be grown in culture media.
(v) Plants can be isolated by creating these conditions in culture medium.
(vi) New hybrid species can be evolved by tissue culture.
(vii) We can select desirable mutants in a relatively small places or in a very short time.
(viii) Useful chemicals can be produced in plant cell culture in liquid media.

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