Edexcel IGCSE Biology

Revision Notes

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, IGCSE & GCSE Chemistry revision notes

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, downloadable IGCSE & GCSE Biology revision notes 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, IGCSE & GCSE Biology revision notes

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, downloadable IGCSE & GCSE Biology revision notes
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, IGCSE & GCSE Biology revision notes

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

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Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. With 10 years of teaching experience across the 3 key science disciplines, Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.
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