Excretion in Plants (Edexcel IGCSE Science)

The Need for Excretion in Plants

Spec point — 3.20 · understand the origin of carbon dioxide and oxygen as waste products of metabolism and their loss from the stomata of a leaf

• Within plant cells there is a range of metabolic reactions taking place producing waste products

• Some of these waste products can be used up in other processes in the plant while some must exit the plant via the leaf organ

• Waste products or substances in excess within a plant can include:

  • Oxygen
  • Carbon dioxide

Oxygen and carbon dioxide

• Oxygen and carbon dioxide can be both reactants and waste products within a plant

• During the day, when there is sufficient light and a plant is photosynthesising:

  • The rate of photosynthesis is higher than the rate of respiration
  • More oxygen is released than is used in respiration
  • Less carbon dioxide is released than is used in photosynthesis
  • Net effect - more oxygen is produced than used

• During the night, when there is insufficient light:

  • There is no photosynthesis, only respiration
  • Oxygen is used in respiration and carbon dioxide is produced
  • No photosynthesis means that no carbon dioxide is used
  • Net effect - more carbon dioxide is produced than used

• Whichever gas is in excess diffuses out of the plant via the leaf organ

  • The gases exit through the stomata

• As the excretion of gases in plants occurs via diffusion it is technically not an active process