Photosynthesis (Cambridge O Level Biology)

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Photosynthesis

  • Photosynthesis can be defined as:

The process by which plants manufacture carbohydrates from raw materials using energy from light

  • Green plants make glucose from the raw materials carbon dioxide and water
  • At the same time, oxygen is made and released as a waste product
  • The green pigment chlorophyll absorbs light energy from the sun, providing the energy needed for the reaction to occur

Examiner Tip

The raw materials required for photosynthesis are carbon dioxide and water. Although required for the reaction to take place, light energy is not a substance and therefore cannot be a raw material.

Photosynthesis Equations

  • The word equation for photosynthesis can be represented as follows:

Photosynthesis word equation diagram

Photosynthesis word equation

The word equation for photosynthesis shows the raw materials and products. Here the additional requirements for light energy and chlorophyll are also indicated

  • The raw materials required by plants are taken up by different plant organs from the plant's environment:

Photosynthesis raw materials diagram

Photosynthesis with additional labels to show the source of raw materials and the fate of products

Plants gain the materials required for photosynthesis from their surroundings

  • Light energy from the sun is converted into chemical energy in the bonds holding the atoms in the glucose molecules together
  • The balanced chemical equation for photosynthesis is:

Photosynthesis balanced chemical equation diagram

Balanced chemical equation for photosynthesis

The chemical symbol for glucose is C6H12O6; to provide enough atoms of carbon, hydrogen and oxygen to produce glucose, 6 molecules of carbon dioxide and 6 molecules of water need to enter the reaction

Examiner Tip

The photosynthesis equation is the exact reverse of the aerobic respiration equation, so if you have learned one you also know the other!

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Naomi H

Author: Naomi H

Expertise: Biology

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.