Higher Biology Unit 3 3 1 Photosynthesis Photosynthesis

Higher Biology Unit 3 3. 1 - Photosynthesis

Photosynthesis • Revision: • Answer these questions on photosynthesis from N 5? • 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?

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

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

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

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

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

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

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

• 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 regions of the spectrum • The other pigments absorb light from other regions and pass the energy onto chlorophyll (these are known as accessory pigments)

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

Chloroplast Structure

• 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