IGCSE Biology Paper-4: Specimen Questions with Answers 254 - 255 of 279

Passage

The diagram shows an Arctic food web.

Arctic Food Web

Question 254 (3 of 3 Based on Passage)

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The phytoplanktons are the producers in this food web. Name the process by which phytoplankton build up stores of chemical energy.

Explanation

The microscopic organisms that live in the surface waters of the sea or fresh water are called, collectively, plankton. The single-celled algae are the phytoplankton. They are surrounded by water, salts, and dissolved carbon dioxide. Their chloroplasts absorb sunlight and use its energy for making food by photosynthesis. Phytoplankton is eaten by small animals in the zooplankton, mainly crustacea. Small fish will eat the crustacea.

Passage

All mammals have a double circulatory system. Fig. shows part of the human double circulatory system.

Muscular Wall of Heart

Question 255 (1 of 3 Based on Passage)

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Describe what is meant by the term double circulation.

Explanation

Double Circulation System

In such system, for one complete circulation through the body, the blood passes twice through the heart:

  • To the lungs and back: It is called Pulmonary circulation or Lesser circulation (due to Lesser distance of the lungs from the heart) .
  • To the body organs and back: It is called Systemic circulation or Greater circulation (covering greater distance from heart to the body − organs. e. g. Amphibians, Reptiles, Birds and Mammals) . (Because of single ventricle, the amphibians and reptiles have incomplete double circulation) .
Pulmonary Vein and Artery