CBSE Guess > Papers > Question Papers > Class X > 2009 > Science > Science

Q. 18. Name the main hormone secreted by thyroid gland and state its one function. 1

Ans. • Thyroxine
• It controls the rate of metabolism of carbohydrates, fats and proteins in the body.

Q. 19. What is meant by renewable natural resources? 1

Ans. The sources of energy which are being produced continuously by nature and are inexhaustible are called renewable sources of energy. For example: Hydel energy, Wind energy, Solar energy, Biomass energy etc.

Q. 20. Write the name and functions of any two parts of the human hind brain. 2

Ans. Pons, Cerebellum and Medulla are the parts of hind brain

• The pons take part in regulating respiration.

• Cerebellum helps to maintain posture and balance of the body.

Q. 21. What is reproduction? What are its two types? Which one of the two confers new characteristics on the offsprings and how? 2.

Ans. The production of new organisms from the existing organisms of the same species is known as reproduction.
There are two main methods of reproduction:
(i) asexual reproduction
(ii) sexual reproduction
The sexual reproduction confers new characteristics on the offsprings because the offspring receives some genes from the mother and some from the father and the mix of genes of mother and father in various different combinations causes genetic variation.

Q. 22. State two problems caused by the non-biodegradable waste that we generate in our daily life. 2

Ans. Problems caused by the non-biodegradable waste:
(i) Non-biodegradable wastes cannot be made less toxic easily and hence they are major pollutants of the environment.
(ii) Non-biodegradable waste can be passed along the food chain from crops to man and other animals and harm them.

Q. 23. Name the hormones secreted by testis and ovary. Write one function each of these hormones. 2

Ans. Testis: hormones–testosterone
• Its function is to control the development of male sex organs and male features.

Ovaries: hormones–oestrogen and progesterone.
• Oestrogen controls the development of female sex organs and female features.
• Progesterone controls the uterus and changes in menstrual cycle.

Q. 24. What is binary fission? Draw a diagram to show binary fission in Amoeba. 2

Ans. Binary fission: See Q.1 (S.A.T.), Chapter 8. [Page 85

Science 2009 Question Papers Class X
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