Edexcel IGCSE Biology 复习笔记 2.7.3 Plants: Gas Exchange in Photosynthesis & Respiration

Edexcel IGCSE Biology 复习笔记 2.7.3 Plants: Gas Exchange in Photosynthesis & Respiration

Gas Exchange: Photosynthesis & Respiration

 

  • 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

 

 

Word-equation-for-aerobic-respiration

 

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)

 

 

 

Gas-exchange-in-respiration

 

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

 

Photosynthesis-word-equation

 

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)

 

 

 

Gas-exchange-in-photosynthesis

 

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

 

 

Gas Exchange: Day & Night

 

  • 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

     

 

 

Photosynthesis-and-respiration-in-plants

 

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

 

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