[2 Mark Questions]

Question 12 Marks

Why is the use of iodised salt advisable?

Answer

Iodine is required by the thyroid gland to make thyroxine hormone. Iodised salt provides iodine needed by thyroid gland to make sufficient thyroxin for our body. The use of iodised salt prevents risk of goitre.

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Question 22 Marks

How do harmful chemicals get accumulated progressively at each trophic level in a food chain?

Answer

Biomagnification is the process by which a harmful chemical enters the food chain and gets get accumulated progressively at each trophic level in a food chain.

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Question 32 Marks

a. Write the percentage of (i) solar energy captured by the autotrophs and (ii) energy transferred from autotrophs to the next level in a food chain.
b. What are trophic levels? Why do different food chains in an ecosystem not have more than four to five trophic levels? Give reason.

Answer

a. In a food chain, autotrophs use around $1 \%$ of sunlight to prepare their own food. After that, all the next levels gain $10 \%$ of the energy that the previous level acquired. For example: Let you have a food chain with 4 levels.
b. Trophic level is defined as the position of an organism in the food chain and ranges from a value of 1 for primary producers to 5 for marine mammals and humans. There is only $10 \%$ flow of energy from one trophic level to the next higher level. The loss of energy at each step is so great that very little usable remains after four or five trophic levels. Hence only 4 to 5 trophic levels are present in each food chain.

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Question 42 Marks

Identify the following diagram and name the parts marked as A, B and C

Answer

Stomata
A. Guard Cell
B. Chloroplast
C. Stoma

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Science [2 Mark Questions]

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