CBSE Guess > Papers > Question Papers > Class X > 2008 >Science > Science Theory

Q. 24. Explain the cause of shoots of the plant bending towards light.

Ans. The plant stem responds to light and bends towards it due to the action of auxin hormone.
(i) When sunlight comes from above, the auxin hormone present in the tip of the stem spreads uniformly down the stem. So the stem grows straight up.

(ii) When the sunlight falls on one side, the auxin hormone prefers to stay in shade as shown in the diagram.

(iii) Due to uneven distribution of auxin hormone, the side with more auxin will grow faster than the other side. Thus, the stem bends towards the side in the direction of light.

Q. 25. What is double circulation in human beings? Why is it necessary?

Ans. Double Circulation. See Q. 29 (S.A.T.), Chapter 6. [Page 66

Q.26. What are biodegradable and non-biodegradable substances? Describe two ways in which non-biodegradable substances affect our environment.

Ans. See Qs.1, 2, 3 and 4 (V.S.A.T.), Chapter 15. [Page 167
Effect of non-biodegradable substances on our environment.
See Q. 12 (S.A.T.), Chapter 15. [Page 170

Q. 27. (a) Name the parts labelled A, B, C, D and E.

Science 2008 Question Papers Class X
Delhi		Outside Delhi		Compartment Delhi		Compartment Outside Delhi
	All Sets (PDF)				Set 1		Set 1
					Set 2		Set 2
					Set 3		Set 3