Gas Exchange: Night vs Day (Edexcel IGCSE Biology (Modular)): Revision Note

Gas Exchange: Night vs Day

• Plants can only photosynthesise when they have sufficient light, however, the cells of plants respire all the time

• This means that gas exchange in plants varies throughout a 24 hour period

• During the day plants both respire and photosynthesise

  • The rate of photosynthesis tends to be higher than the rate of respiration (unless light intensity is low)

  • Therefore there is a net diffusion of carbon dioxide into the plant and a net diffusion of oxygen out of the plant during the day

• During the night, plants only respire

  • This means that there is a net movement of oxygen into the plant and a net diffusion of carbon dioxide out of the plant during the nighttime

• At low light intensities, the rate of photosynthesis is equal to the rate of respiration

  • This means that there is no net movement of oxygen or carbon dioxide in either direction

Plants photosynthesise and respire during the day but only respire at night time