Photosynthesis

Nature of science:

Experimental design—controlling relevant variables in photosynthesis experiments is essential. (3.1)

• Photosynthesis is the production of carbon compounds in cells using light energy.
• Visible light has a range of wavelengths with violet the shortest wavelength and red the longest.
• Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.
• Oxygen is produced in photosynthesis from the photolysis of water.
• Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
• Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.

Applications and skills:

• Application: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis.
• Skill: Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis.
• Skill: Design of experiments to investigate the effect of limiting factors on photosynthesis.
• Skill: Separation of photosynthetic pigments by chromatograph. (Practical 4)

• Syllabus and cross-curricular links:
• Biology
• Topic 2.5 Enzymes

• Students should know that visible light has wavelengths between 400 and 700 nanometres, but they are not expected to recall the wavelengths of specific colours of light.
• Water free of dissolved carbon dioxide for photosynthesis experiments can be produced by boiling and cooling water.
• Paper chromatography can be used to separate photosynthetic pigments but thin layer chromatography gives better results.