• The processes of?respiration?and?photosynthesis?both rely on the exchange of oxygen and carbon dioxide

Gas exchange during respiration

• All living cells respire
• The process requires the uptake of?oxygen?and the release of?carbon dioxide

The respiration equation

• The oxygen diffuses down the concentration gradient from a?high concentration?(outside the leaf) to a?low concentration?(inside the leaf)
  • The cells use oxygen in respiration so the concentration is always low inside the respiring cells

   

• The carbon dioxide diffuses down the concentration gradient from a?high concentration?(inside the leaf) to a?low concentration?(outside the leaf)

In respiration, carbon dioxide diffuses out of the leaf and oxygen diffuses into the leaf

Gas exchange during photosynthesis

• Plant cells photosynthesize when there is enough?sunlight
• The process requires the uptake of?carbon dioxide?and the release of?oxygen

The photosynthesis equation

• The carbon dioxide diffuses down the concentration gradient from a region of?high concentration?(outside the leaf) to a region of?low concentration?(inside the leaf)
  • The cells use carbon dioxide in photosynthesis so the concentration is always low inside the photosynthesizing cells

   

• The oxygen diffuses down the concentration gradient from a?high concentration?(inside the leaf) to a?low concentration?(outside the leaf)

In photosynthesis, carbon dioxide diffuses into the leaf and oxygen diffuses out of the leaf

• Plants can only photosynthesize 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 photosynthesize
  • 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 photosynthesize and respire during the day but only respire at night time