Q21 of 58 Page 1

What is pollination? How does it occur in plants? How does pollination lead to fertilization? Explain.

Pollination: It is a type of asexual reproduction in which the pollen grains are transferred from the anther of a stamen to stigma of a carpel. Pollination is of two types:


(a) Self-pollination: Self-pollination is the process of transfer of pollen grain from anther of a flower to the stigma of same flower or another flower of the same plant.


(b) Cross-pollination: It is defined as the process of transfer of pollen grains from the anther of a flower to the stigma of flower belonging to other similar plant.


Stigma receives the pollen grains from anther of stamen during the process of pollination. When a pollen falls on Stigma, it bursts open and grows a pollen tube downward through style towards female gamete in ovary. A male gamete moves down the pollen tube. The female gamete also known as Ovum combines with the male gamete to form zygote.


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Write the two causes of human population explosion. Explain with the help of suitable example show this explosion can be checked.

 22

(a) To construct a ray diagram we use two light rays which are so chosen that it is easy to know their directions after reflection from the mirror. List these two rays and state the path of these rays after reflection. Use these two rays to locate the image of an object placed between infinity and the center of curvature of a concave mirror.

(b) Draw a ray diagram to show the formation of image of an object placed between the pole and principal focus of a concave mirror. How will the nature and size of the -image formed change, if the mirror is replaced by a converging lens of same focal length?

 23

(a) A student cannot see clearly a chart hanging on a wall placed at a distance of 3 from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this effect . List its two possible causes.

(b) Draw a ray diagram to show how this defect maybe corrected using a lens appropriate focal length.


(c) An eye donation camp is being organized by social workers in your locality. and why would you help in this cause?