IGCSE Biology Paper-2: Specimen Questions with Answers 136 - 136 of 203

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Question 136



Breathing out combines which of the following two characteristics of living organisms?


Choice (4)


Inspiration and expiration


Excretion and respiration


Excretion and movement


Movement and sensitivity





  • The lungs supply the body with oxygen, but they are also excretory organs because they get rid of carbon dioxide. They are responsible for the excretion of gaseous wastes from the body.
  • The main waste gas excreted by the lungs is carbon dioxide, which is a waste product of cellular respiration in cells throughout the body. Carbon dioxide is diffused from the blood into the air in the tiny air sacs called alveoli in the lungs. By expelling carbon dioxide from the blood, the lungs help maintain acid-base homeostasis.
  • In fact, it is the pH of blood that controls the rate of breathing. Water vapor is also picked up from the lungs and other organs of the respiratory tract as the exhaled air passes over their moist linings, and the water vapor is excreted along with the carbon dioxide.
  • Trace levels of some other waste gases are exhaled, as well. So considering breathing continues with respiration and excretion of carbon dioxide gases.

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