Photosynthesis

1. Chloroplast = organelle cotaining photosystem (where photosynthesis occurs).
2. A photosystem consists of:
• chlorophyll molecules (primary pigment)
• accessory pigments (chrolophyll b and carotenoids)
• proteins
• associated electron acceptors.
3. PS I (photosystem I) absorbs light of wavelength 700nm
4. PS II (photosystem II) adsorbs light of wavelength 680nm
5. Paper chromatography technique = to separate different pigments of a leaf.
6. Each pigment is identified by the characteristic coloured peak formed on the chromatography paper.
7. The amount of absorption of the pigments and the rate of photosynthesis at different wavelength of light can be graphically represented.
8. Absorption spectrum = indicates the amount of absorption at different wavelengths of light.
9. Action spectrum = indicates the rate of photosynthesis at different wavelengths of light.
10. Chlorophyll a and chlorophyll b absorb blue and red light
11. Carotenoids absorb only blue light.
12. The absorption spectrum and action spectrum graphs show peaks and valleys.
13. Engelmann conducted a series of experiments using filamentous algae. He used the motile, oxygen sensitive bacteria call Pseudomonas sp.
14. Chloroplasts were illuminated with different wavelengths of light and the movement of the bacteria was observed.
15. Bacteria were found to group around the region of the chloroplasts illuminated by red and blue wavelengths of light.
16. Engelmann concluded from the experiments that photosynthesis can occur only when the chloroplasts are illuminated by red and blue light