Circulatory System - Sample Question (1)

During Science examinations, pupils are often required to use comparison skills when answering open-ended questions. Below is a sample question on the circulatory system.

The diagram below shows how blood flows in certain parts of the body.

(a) The blood at D contains a greater amount of a substance than at C. What is this substance? Give a reason for your answer.

Answering Technique:

Comparison is needed as there is a comparative word "greater" in the question stem. 

Focus only on carbon dioxide in your explanation.

Carbon dioxide. The blood at D flows from the legs where the body cells give out carbon dioxide when they carry out cellular respiration. The blood at C flows from the heart which flows from the lungs where carbon dioxide has been expelled from the body 

(b) Why is the amount of oxygen in the blood lower at A than at B?

Answering Technique:

Comparison is needed as there is a comparative word "lower" in the question stem. 

Focus only on oxygen in your explanation.

The blood at A flows from the head and the legs where the body cells take in oxygen when they carry out cellular respiration. The blood at B flows from the heart which flows from the lungs where oxygen from the inhaled air passes through the walls of the air sacs into the blood.