National 4/5 Biology

1. National 4/5 Biology Section 4: The chemistry of photosynthesis The need for light, chlorophyll and carbon dioxide

2. Problem to solve • What substances are required for photosynthesis? - light - chlorophyll - carbon dioxide • How would you prove chlorophyll and carbon dioxide are necessary for photosynthesis using the apparatus on the desk? (Hint: you have completed a similar practical in S1) • Carry out experiment

3. What are we learning today? • We are learning to: - state that photosynthesis is a two stage process - explain why light and chlorophyll are necessary for photosynthesis - explain why carbon dioxide is necessary for photosynthesis • Success criteria - Two stages photolysis and carbon fixation - Photolysis, light trapped by chlorophyll to split water in to hydrogen and oxygen - Carbon fixation, carbon dioxide source of carbon for glucose

4. The need for light • From S1 Physical science you learned that visible light is split in to the colours you can see here • During photosynthesis plants convert light energy in to chemical energy (glucose)

5. How do plants trap light? reflected absorbed The absorbed light is used for photosynthesis Video clip - Light and starch - Science & Plants for Schools transmitted

6. Structure of a leaf phloem xylem Guard cells

7. Structure of the leaf continued • The palisade mesophyll and spongy mesophyll cells have chloroplasts • Chloroplasts contain the green pigment chlorophyll which is required to trap light

8. Chloroplasts • Chloroplasts are the site of photosynthesis • Video clip - chloroplasts and starch - Science & Plants for Schools Stroma – liquid filling Starch grains – store of glucose Grana membranes containing pigments e.g. chlorophyll

9. Two stages of photosynthesis • Photosynthesis is more than the one line word equation we know so far. • Photosynthesis is a series of enzyme controlled reactions that enable plants to make their own food. • There are two stages of photosynthesis. • The two stages of photosynthesis are: - photolysis - carbon fixation

10. Photolysis – occurs in grana Light energy is used to split water in to hydrogen and oxygen NADP is a hydrogen acceptor that is used to transport the hydrogen to the stroma for carbon fixation Waste product of photosynthesis Light energy is use to make ATP (energy molecule) also used in carbon fixation = photophosphorylation

11. Why is carbon dioxide required for photosynthesis? • Revision!! • Carbon dioxide is required as the source of carbon to make glucose Carbon dioxide + Water Glucose + Oxygen CO2H2OC6H12O6O2

12. Carbon fixation – occurs in stroma • Several enzyme controlled reactions • Requires energy in the form of ATP from photolysis • Carbon (from CO2) becomes ‘fixed’ into carbohydrate • The carbon combines with hydrogen from photolysis to form glucose

13. Carbon fixation NADPH2 NADP ATP Carbon dioxide (CO2) ADP + Pi Glucose

14. What happens to the glucose? • Revision!! • Glucose converted into storage carbohydrate – starch • Glucose also converted into cellulose - a component of cell walls

15. What have I learned today? • Exit ticket • On your exit ticket write down (if you can) the summary of photolysis and carbon fixation