MathsGradeUp logoMathsGradeUp
BiologyGCSE, IGCSE & A Level

What is photosynthesis?

Photosynthesis is the process by which plants use light energy to convert carbon dioxide and water into glucose and oxygen.

Photosynthesis explained

It happens in chloroplasts, where chlorophyll absorbs light. The light-dependent stage produces ATP and reduced NADP; the light-independent stage fixes carbon dioxide into sugars.
Light intensity, carbon dioxide concentration and temperature can each limit the rate — whichever is furthest from its optimum is the limiting factor.

Key formula

6CO2+6H2O→lightC6H12O6+6O26\mathrm{CO_2} + 6\mathrm{H_2O} \xrightarrow{\text{light}} \mathrm{C_6H_{12}O_6} + 6\mathrm{O_2}

Worked example

On a bright but cold day, temperature limits photosynthesis even though light is plentiful.

Examiner tip

On a rate graph, identify the limiting factor from the plateau: the flat section shows another factor has taken over.

Photosynthesis: common questions

What is a limiting factor?
The factor in shortest supply that caps the rate; increasing any other factor has no effect until it is raised.
Do plants respire as well as photosynthesise?
Yes, continuously. During the day photosynthesis usually exceeds respiration, so there is a net release of oxygen.

Related terms

Respiration

Respiration is the enzyme-controlled release of energy from glucose in every living cell, transferring it to ATP.

Enzyme

An enzyme is a biological catalyst — a protein that speeds up a specific reaction by lowering its activation energy.

Practise biology on MathsGradeUp

Take photosynthesis from a definition to full marks with exam-board question banks, revision notes and instant step-by-step feedback from Study Coach.

Biology revision notesPractice questionsCreate a free account

Related on MathsGradeUp

Keep studying

Practise it