Revision Notes

6.1 Photosynthesis

Photosynthesis Theory: Basics

  • Green plants make the carbohydrate glucose from the raw materials carbon dioxide and water
  • At the same time oxygen is made and released as a waste product
  • The reaction requires energy which is obtained by the pigment chlorophyll trapping light from the Sun
  • So photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light
  • It can be summed up in the following equation:


Photosynthesis word equation, IGCSE & GCSE Biology revision notesPhotosynthesis word equation


How plants get the materials they need, IGCSE & GCSE Biology revision notesHow plants get the materials they need

Exam Tip

If asked for the raw materials required for photosynthesis, the answer is 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.

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Photosynthesis Theory

  • The balanced chemical equation for photosynthesis is:


Balanced chemical equation for photosynthesis, IGCSE & GCSE Biology revision notesBalanced chemical equation for photosynthesis


  • The light energy is converted into chemical energy in the bonds holding the atoms in the glucose molecules together

Exam Tip

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

You will usually get more marks for providing the balanced chemical equation than the word equation.

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The Products of Photosynthesis

  • Plants use the glucose they make as a source of energy in respiration
  • They can also convert it into starch for storage, into lipids for an energy source in seeds, into cellulose to make cell walls or into amino acids (used to make proteins) when combined with nitrogen and other mineral ions absorbed by roots


The fate of glucose, IGCSE & GCSE Biology revision notesThe fate of glucose

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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