2.44B Gas Exchange: Night vs Day (Edexcel IGCSE Biology)

• Plants can only photosynthesise when they have access to light, however, cells respire all the time
• This means that gas exchange in plants varies throughout a 24 hour period
• During the daytime plants both respire and photosynthesise
  • The rate of photosynthesis tends to be higher than the rate of respiration (unless there is a low light intensity)
  • Therefore there is net diffusion of carbon dioxide into the plant and net diffusion of oxygen out of the plant during the day

• During the nighttime, plants only respire
  • This means that there is a net movement of oxygen into the plant and net diffusion of carbon dioxide out of the plant during the night time

• 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