Higher Biology

1. Higher Biology Photosynthesis Mr G Davidson

2. Pigments and Light • White light is a form of radiant energy • it travels in the form of waves. • These waves always travel in straight lines. G Davidson

3. Pigments and Light • White light can be split into its coloured component if it is passed through a glass prism: • Red • Orange • Yellow • Green • Blue • Indigo • Violet. G Davidson

4. Pigments and Light • Each colour of the spectrum has a different wavelength • The wavelength of light is measured in nanometres (nm) • 1 nm = 10-9m (1/1,000,000,000th metre) • red the longest – around 700 nm • violet the shortest – around 400 nm G Davidson

5. Photosynthesis • Visible white light from the sun is the source of energy for photosynthesis. • Pigments in the leaf absorb light G Davidson

6. Photosynthesis • When it strikes a green leaflight is absorbedby these pigments • A small percentage of this is used in photosynthesis. • The remainder of the light is either reflectedfrom the leaf or transmitted through the leaf. G Davidson

7. Photosynthesis • Most leaves are green because they reflect green light and transmit green light. • Each of the pigments present in a leaf absorbs light of certain wavelengths therefore if a plant has different pigments, it can absorb a wider range of wavelengths of light. G Davidson

8. Absorption Spectrum Wavelength (nm) G Davidson

9. Photosynthesis • The pigments found in plants depend largely on where the plant is to be found e.g. shady plants need more pigment than canopy plants • Different sea weeds have a different range of pigments because of the reducing light intensity at greater depths of water. G Davidson

10. 100 % Sunlight 12 % reflected Only a small percentage of absorbed light is used in photosynthesis 83 % absorbed 5 % transmitted Fate of Light Striking a Leaf G Davidson

11. Granum Double unitmembranes Lamella Stroma Chloroplasts G Davidson

12. Chloroplast G Davidson

13. Chloroplasts • The light trapping pigments are to be found in the chloroplasts of plant cells. • Chloroplasts are relatively large organelles found in the cytoplasm, each one surrounded by a double unit membrane. • Inside the chloroplast are large starch grains which act as food stores. G Davidson

14. Chloroplasts • The main components of the chloroplast are grana which are interconnected by lamellae. • The grana are composed of flattened discs containing the pigments, and are the site of the light reaction. • The stroma is the site of carbon fixation and is the fluid part in the chloroplast. G Davidson

15. Carbon dioxide CO2 water H2O glucose C6H12O6 oxygen O2 Light Pigments Chemistry of Photosynthesis • In the process of photosynthesis, raw materials carbon dioxide and water are assembled to make organic food molecules producing oxygen as a waste product. G Davidson

16. Chloroplasts • Photosynthesis occurs in two stages. • The first stage requires light and is called the light reaction or photolysis. • The second stage is a temperature dependent series of enzyme controlled reactions called carbon fixation or the Calvin Cycle. G Davidson

17. Photolysis • This is the trapping of sunlight energy by photosynthetic pigments to release chemical energy. • The light energy splits water into hydrogen and oxygen, the oxygen then being released as a by-product. • The hydrogen then combines with a hydrogen acceptor NAD to produce NADH2. G Davidson

18. Photolysis • At the same time, energy is also made available to convert ADP + Pi into the high energy molecule ATP. • This is a process known as photophosphorylation. • The NADH2 and ATP made by photolysis are passed to the carbon fixation stage. • Photolysis occurs on the grana of the chloroplasts. G Davidson

19. Sunlight CO2 NADH2 Water Photolysis Carbon Fixation Oxygen Photo- phosphorylation ATP Sugar Photolysis G Davidson

20. Calvin Cycle • This is also referred to as carbon fixation. • This stage is a series of enzyme controlled chemical reactions in the form of a cycle. G Davidson

21. Calvin Cycle • As the carbon dioxide enters carbon fixation, it combines with a 5 carbon ribulose biphosphate (RuBP) to form an unstable 6 carbon compound which immediately splits into two molecules of 3 carbon glycerate phosphate. G Davidson

22. 1C 5C 6C Glucose CO2 RuBP ADP + Pi ATP 6 Carbon compound Triose phosphate 6C 3C NAD NADH2 Glycerate phosphate ADP + Pi ATP 3C Calvin Cycle G Davidson

23. Calvin Cycle • Two molecules of glycerate phosphate are then converted via a triose phosphate into 6C sugar, using hydrogen and energy – both provided by photolysis. G Davidson

24. Calvin Cycle • Two molecules of triose phosphate are then used to make one molecule of 6 carbon glucose, which are then built to form starch or cellulose. G Davidson

25. Calvin Cycle • Not all triose phosphate molecules are used to make sugar, some are required to continue the cycle i.e. take it back to RuBP. • In doing this 5 molecules of 3 carbon triose phosphate become 3 molecules of 5 carbon RuBP using energy from ATP and so the Calvin cycle is allowed to continue. G Davidson

26. Limiting Factors • Chemical reactions such as photosynthesis can be speeded up or slowed down depending on certain conditions. • A condition which is able to limit the rate of a reaction is usually called a limiting factor. G Davidson

27. Elodea Bubbler • In the Elodea bubbler experiment we can alter light intensity, CO2 concentration and temperature, one at a time to show that they are all limiting factors. • The rate of photosynthesis is measured by counting the bubbles of oxygen released in a specific time. G Davidson

28. 0.5% solution of sodium bicarbonate to provide a supply of CO2 Constant temperature Elodea Bubbler G Davidson