IGCSE Biology Paper-2: Specimen Questions with Answers 152 - 152 of 203

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Question 152



Which two gases are the biggest contributors to the greenhouse effect?


Choice (4)


Carbon dioxide and ozone


Sulfur dioxide and methane


Carbon monoxide and carbon dioxide


Carbon dioxide and methane




  • The green house is a small glass house using for growing plants especially during winter.
  • In a greenhouse the glass panel lets the light (with long wave- infrared – radiation) in, but does not allow heat (with short wave infrared) to escape. Therefore, the greenhouse warms up very much like inside of a car that has been parked in the sun for a few hrs.
  • The term ‘Green House Effect’ is derived from this phenomenon of greenhouse. A naturally occurring phenomenon is responsible for heating of earth surface and atmosphere.
  • Without a greenhouse effect, the average temperature at earth surface would have been around , rather than the present average of .
  • The sunlight or solar energy when enters into atmosphere about of it is reflected back due to clouds and gases in the outermost atmosphere, some of it is absorbed, and about half of solar radiation falls on the earth surface for heating it, though a small proportion of it is reflected back from earth.
  • The earth surface re-emits heat in the form of long wave infra- red radiation, but a major fraction of it is absorbed by atmospheric gases and does not escape into space.
  • The molecules of these gases radiate heat energy. A major part of this comes or falls on to earth surface, thus heating it up once again. This cycle is repeated many a times to warm-up the earth, and continues until the earth-surface does not have longer wave- radiations to emit. The carbon-di-oxide and methane are the main greenhouse gases.
  • The relative contribution of various greenhouse gases to global warming is

Carbon Dioxide and Methane

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