Gas Exchange

Gas exchange in plants takes place in the leaves. Gas exchange in plants is required for two critical processes.

  1. Respiration
  2. Photosynthesis

 

Respiration

Respiration is the release of energy from the breakdown of glucose in living cells. Respiration takes place in every living cell and all cells need to respire to produce the energy they need. Respiration involves the intake of oxygen and giving out of carbon dioxide. Respiration takes place all the time.

The equation for respiration is:

glucose + oxygen
C6H12O6 6O2
carbon dioxide + water + energy
6CO2 6H2O  

 

 



Photosynthesis

Photosynthesis is the process in which green plants produce glucose. It involves the conversion of carbon dioxide gas, water and minerals the plants take in from their surroundings into sugar and gaseous oxygen.

The equation for photosynthesis is given as:

carbon dioxide + water
6CO2 6H2O
light energy

chlorophyll
glucose + oxygen
C6H12O6 6O2

 

Photosynthesis involves the intake of carbon dioxide and the release of oxygen. As it requires radiant energy it only takes place in the light.


The table below summaries the two process involving gas exchange in green plants.

Process Respiration Photosynthesis
Gas In Oxygen Carbon Dioxide
Gas Out Carbon dioxide, water vapour Oxygen
Time At all times – day and night Requires sunlight – daytime only
Equation glucose + oxygen
carbon dioxide + water + energy
carbon dioxide + water
glucose + oxygen

 

Photosynthesis can be considered as the opposite or reverse to respiration in green plants. Thus, if you remember the equation for one of the processes you can easily recall the other.

 

The movement of gases in and out of green plants is via a process called diffusion. The route of the gases in and out of the leaves is regulated by the stomata.