1.7 Photosynthesis

1. 1.7Photosynthesis

2. Energy Fixation • Photosynthesis is the process by which green plants make their own food using light energy • The light energy is captured by the green pigment chlorophyllwhich is found in chloroplasts • Light energy is converted into chemical energy in the form of ATP.

3. Photosynthesis • Carbohydrates such as glucose are formed during photosynthesis from the raw materialscarbon dioxide and water • Light energy and chlorophyll are also required but are not used up therefore are not raw materials • Oxygen is produced as a by-product from the splitting of water (H2O) into hydrogen and oxygen

4. Importance to Animals • Photosynthesis is needed by a plant to manufacture its own food. • Why is it important to animals? • [Think about the products]

5. Carbon Dioxide + WaterLight EnergyChlorophyll Glucose + Oxygen

6. Testing for Starch

7. Testing for Starch • If starch is present in a leave, iodine solution will turn the leaf blue-black. • Plant L was left in sunlight • Plant D was left in the dark • What do you think will happen when a leaf from each plant is tested? L D

8. Animation of method • Watch this clip if you need extra help with the method. • Starch testing animation

9. Photosynthesis • Glucose formed during photosynthesis is used by the plant cells to carry out respiration to provide energy for all the cells reactions • Some glucose is converted to starch for storage • Some glucose is converted to cellulose to build cell walls

10. DARK DIM BRIGHT LIGHT DIM DARK Dry mass of leaf Midnight Noon Midnightt Starch Production on 24h Time of Day

11. Variegated leaf

12. sodium bicarbonate sodium hydroxide Need for Carbon Dioxide

13. Products Raw materials Conditions + + Summary http://www.twigonglow.com/films/photosynthesis-1186/

14. Leaf Structure

15. Leaf Structure

16. Photolysis • http://www.twigonglow.com/films/photosynthesis-1186/ • The first stage of photosynthesis is photolysis - the splitting of water • Light energy is captured by the chlorophyll in chloroplasts and used to split water into oxygen gas and hydrogen • The oxygen diffuses out of the cell.

17. ADP + Pi ATP (energy) O2 passed to second stage released as gas passed to second stage Photolysis The sun Light energy absorbed by chlorophyll Hydrogen acceptor H2 Water (H2O) Reduced hydrogen acceptor

18. Carbon Fixation • The second stage of photosynthesis is carbon fixation • Carbon Dioxide undergoes a series of enzyme controlled reactions and combines with the hydrogen from photolysis to form glucose. This also requires the ATP which was formed in photolysis. • Both stages of photosynthesis occur in the chloroplast

19. Carbon Fixation Energy Hydrogen ATP ADP + Pi Reduced hydrogen acceptor (loaded with H2) Glucose Stored as starch or used to make cellulose CO2

20. Reaction in chloroplast

21. Starch and Cellulose

22. Limiting Factors • A limiting factor is some factor which when in short supply prevents photosynthesis proceeding more quickly • The rate of photosynthesis can be measured by • The production of oxygen • The uptake of carbon dioxide • The production of carbohydrate

23. Limiting Factors • The rate of photosynthesis may be limited by • Light Intensity • Carbon dioxide concentration • Temperature • Removing any limiting factor allows early crops to be produced

24. The Elodea Bubbler • Elodea is a type of pondweed. • It is a good plant to use to study the effects that limiting light has on photosynthesis • Use this link to perform a virtual version of this experiment or look at the demo set up to answer the questions. • Use Multimedia Science to collect data

25. Questions for the Elodea Bubbler experiment • Plot your results on a graph. • How does the distance from the light source relate to the light intensity? • What gas do you think the bubbles contain? • Using your data and your graph, describe the trend that it shows. Why do you think this trend occurs? • Can you think of any other factors, apart from light intensity, which could affect the rate of photosynthesis in Elodea? How do factors affect photosynthesis? • How could you improve this experiment to achieve more precise, accurate and reliable results?

26. Results

27. Light intensity as a Limiting Factor • Look at this graph. What does the graph show us about light intensity as a limiting factor?

28. Light Intensity as a Limiting Factor • Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis to a certain rate where it will then level off. At this point it cannot increase anymore.

29. Results

30. Carbon dioxide concentration as a limiting factor • What does this graph tell us about carbon dioxide concentration on the rate of photosynthesis?

31. Carbon dioxide concentration as a limiting factor • Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is not enough carbon dioxide available.

32. Results

33. Temperature as a limiting factor • What does this graph tell us about temperature as a limiting factor on the rate of photosynthesis?

34. Temperature as a limiting factor • If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot.