[2 Mark Questions]

Question 12 Marks

i. State the function of the following plant hormones
a. Abscisic acid
b. Cytokinin
ii. Define chemotropism

Answer

i. a. Abscisic acid
- inhibits growth
- promotes dormancy in seeds and buds.
- Promotes closing of stomata.
b. Cytokinin
- promotes cell division
- delays aging in leaves
- promotes fruit growth.
ii. Chemotropism - It is the directional movement or orientation of the plant part in response to chemical stimulus.

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Question 22 Marks

What is an ecosystem? Give one example each of
i. natural, and
ii. man-made ecosystem.

Answer

The interaction of living organism with the non-living components in an area of the environment is called as ecosystem.
i. Natural: forests / deserts / oceans / ponds / lakes
ii. Man-made: crop field / garden / aquarium / zoo

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Question 32 Marks

a. Explain the role of UV radiation in producing ozone layer.
b. Mention the reaction involved.
c. Why is excessive use of CFCs a cause of concern?

Answer

a. High energy UV radiations split apart some molecular oxygen into free ( O ) atoms, these atoms combine with molecular
b. The reaction involved.
$\mathrm{O}_{2} \xrightarrow{\mathrm{UV}} \mathrm{O}+\mathrm{O} $
$\mathrm{O}+\mathrm{O}_{2} \rightarrow \underset{\text { (Ozone) }}{\mathrm{O}_{3}}$
c. Depletion of the ozone layer.
If these UV radiations reach the earth they may cause skin cancer in human beings.

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Question 42 Marks

Explain the events that take place once a sperm reaches the oviduct till it becomes a foetus. Write the role of placenta in pregnancy.

Answer

i. In the oviduct, sperm encounters the egg and fertilisation takes place.
ii. The fertilized egg (zygote) starts dividing and forms a ball of cells or embryo.
iii. Embryo is implanted in the lining of the uterus, where it continues to grow and develops organs to become a foetus.
iv. Role of Placenta:
- Provides a large surface area for glucose and oxygen to pass from the mother to the embryo.
- Waste generated by the embryo will be removed by transferring them into the mother's blood.

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Science [2 Mark Questions]

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