CIE IGCSE Biology: 复习笔记:6.1.7 Investigating Gas Exchange

CIE IGCSE Biology: 复习笔记:6.1.7 Investigating Gas Exchange

Investigating Gas Exchange

  • Plants are respiring all the time and so plant cells are taking in oxygen and releasing carbon dioxide as a result of aerobic respiration
  • Plants also photosynthesise during daylight hours, for which they need to take in carbon dioxide and release the oxygen made in photosynthesis
  • At night, plants do not photosynthesise but they continue to respire, meaning they take in oxygen and give out carbon dioxide

Photosynthesis and respiration in plants

  • During the day, especially when the sun is bright, plants are photosynthesising at a faster rate than they are respiring, so there is a net intake of carbon dioxide and a net output of oxygen
  • We can investigate the effect of light on the net gas exchange in an aquatic plant using a pH indicator such as hydrogencarbonate indicator
  • This is possible because carbon dioxide is an acidic gas when dissolved in water
  • Hydrogencarbonate indicator shows the carbon dioxide concentration in solution
  • The table below shows the colour that the indicator turns at different levels of carbon dioxide concentration

  • Several leaves from the same plant are placed in stoppered boiling tubes containing some hydrogencarbonate indicator
  • The effect of light can then be investigated over a period of a few hours
  • Results from a typical experiment are shown in the table below: