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12th Biology 2013 Set1 Delhi Board Paper Solution

Question 28

(a) Draw a diagrammatic sectional view of a mature anatropous ovule and label the following parts in it:
(i) that develops into seed coat.
(ii) that develops into an embryo after fertilization.
(iii) that develops into an endosperm in an albuminous seed.
(iv) through which the pollen tube grains entry into the embryo sac.
(v) that attaches the ovule to the placenta.
(b) Describe the characteristic features of wind pollinated flowers.
OR
(a) Draw a diagrammatic sectional view of the female reproductive system of human and label the parts:
(i) where the secondary oocytes develop
(ii) which helps in collection of ovum after ovulation
(iii) where fertilization occurs
(iv) where implantation of embryo occurs.
(b) Explain the role of pituitary and the ovarian hormones in menstrual cycle in human females.

Answer

mature anatropous ovule

 

(b) Characteristics of wind pollinated flowers:
(i) Large number of pollen grains are produced.
(ii) Pollen grains are light and non-sticky.
(iii) Well exposed stamens so that pollen grain are easily dispersed.
(iv) Large and feathery stigma to trap pollen grains.
 
                                     OR
 
Ans. (a)

view of the female reproductive system of human

 

(b) Changes hapenning in ovary and uterus during menstrual cycle are caused by change in the levels of pituitary and ovarian hormones.
 
After menstrual phase gonadotropin i.e., Luteinising hormone (LH) and follicular stimulating hormone (FSH) are released from pituitary. Their level gradually increases during follicular phase and it stimulates development of follicles and secretion of estrogen by growing follicles.
 
Both LH and FSH attain peak on 13th & 14th day.
 
Rapid secretion LH causes ovulation on day 14.
 
During luteal phases Graafian follicle changes to corpus luteum which secretes Progesterone Progesterone maintains endometrium which is necessary for
implantation.