Photosynthesis and respiration in plants

Plant cells respire, just as animal cells do. If they stop respiring, they will die. Remember that respiration is not the same as breathing, so take care - plants do not breathe.

Here is the word equation for aerobic respiration:

curriculum-key-fact
glucose + oxygen → carbon dioxide + water

Here is the word equation for photosynthesis:

curriculum-key-fact
carbon dioxide + water → glucose + oxygen

The word equations show that the reactants and products of aerobic respiration and photosynthesis are opposites:

  • aerobic respiration uses oxygen and produces carbon dioxide
  • photosynthesis uses carbon dioxide and produces oxygen

Plants respire all the time, whether it is dark or light. They photosynthesise only when they are in the light.

ConditionsPhotosynthesis v respirationOverall result
DarkRespiration but no photosynthesisOxygen taken in, carbon dioxide given out
Dim lightPhotosynthesis rate equals respiration rateNeither gas is taken in or given out
Bright lightPhotosynthesis rate greater than respiration rateCarbon dioxide taken in, oxygen given out

Photosynthesis usually results in a gain of glucose once respiration has been accounted for. Plants that lose their leaves in winter store food produced during the summer by photosynthesis. They store enough food to last them over winter, and to provide energy reserves for new growth in the spring. They are called deciduous plants.

Respiration and photosynthesis in plants