1. Higher Biology
Unit 3
3.1 - Photosynthesis

2. Photosynthesis Revision:
Answer these questions on photosynthesis from N5?
What is the photosynthesis word equation?
How many stages are there to photosynthesis?
Give 2 examples of the uses of the product of photosynthesis?
What is the name of the chemical that traps light during photosyntheis?

3. Light
Photosynthesis is the process by which green plants trap light energy and use it to produce carbohydrates
Light is a form of electromagnetic energy that travels in waves

4. The distance between two crests on a wave is called the wavelength and is measured in nanometres (nm). (1 nm = 10-9 m)
Wavelength

5. Visible Light
The spectrum of visible light is a band of light with wavelengths between 380nm and 750nm

6. Absorption, transmission and reflection
When light comes into contact with a substance it can be absorbed, transmitted or reflected

7. Light absorption by leaves
Leaves contain several pigments that absorb light
The different pigments in a leaf cell absorb different wavelengths of light

8. Leaf Pigments The main pigments in leaves are: Chlorophyll a
Chlorophyll b
Carotene
Xanthophyll

9. Absorption Spectrum
This shows the wavelengths of light absorbed by each pigment found in leaves
Action Spectrum
This shows the effectiveness of different wavelength of light at bringing about photosynthesis

10. When the absorption and action spectra are compared a close correlation is found to exist
Chlorophyll a and b absorb light mainly from the blue and red regions of the spectrum
The other pigments absorb light from other regions and pass the energy onto chlorophyll (these are known as accessory pigments)

11. Having pigments that are able to absorb light at different wavelengths means that the plant is able to photosynthesis more effectively

12. Chloroplast Structure

13. Photosynthetic pigments are contained within the grana of the chloroplasts
This is therefore where absorption of light energy and photosynthesis take place
Carbon fixation takes place in the stroma of the chloroplast