IGCSE Biology Paper-4: Specimen Questions with Answers 7 - 8 of 279

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Question 7

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What do you mean by food web? Write its characteristics and significance.

Explanation

Food chain never occur independently so overlapping of different food chains is called as food web. Food web is important to maintain the balance of ecosystem.

Image Shows a Food Web

Characteristics of food web:

  • Food webs are more real than food chain
  • It consist of number of food chains interconnected
  • Food web is not straight
  • It provide alternate source of food

Significance:

  • They help in maintaining the ecological balance
  • They help in understanding the feeding relations among organism
  • It explains the concept of bio magnification

Question 8

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What do you mean by HIV? How it affects immune system.

Explanation

AIDS (Acquired Immune Deficiency Syndrome) is a disease caused by the human immunodeficiency virus HIV. The human immunodeficiency virus is known for targeting the T-lymphocyte cells of the immune system. HIV attacks and kills crucial immune system cells, known as T-helper cells. Without T-helper cells many other immune system cells cannot not work properly, including B-cells that make antibodies.

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