Photosynthesis. Intermediate 2 Biology

Transcription

1 Photosynthesis Intermediate 2 Biology

2 Learning Objectives - Energy Fixation State that photosynthesis a series of enzymecontrolled reactions by which green plants make their own food. State that sunlight is the source of energy for this stage (including the role of chloroplasts, chlorophyll and ATP). Give the summary equation for photosynthesis (including raw materials, products and by products).

3 Photosynthesis Photosynthesis is the process in which green plants make their own food It is a series of enzyme controlled reactions

4 Trapping light energy Light energy is trapped ( fixed ) by chlorophyll Chlorophyll is found in chloroplasts

5 Photosynthesis Light energy is converted into chemical energy stored in ATP and then chemical energy of carbohydrates

6 Raw Materials Carbohydrates are compounds that consist of Carbon C Hydrogen H Oxygen O

7 Making carbohydrates Carbon dioxide (CO 2 ) and the hydrogen (H 2 ) from water form carbohydrates such as glucose (C 6 H 12 O 6 ) This occurs in the presence of chlorophyll and light energy Oxygen (O 2 ) is produced as a by-product

8 Photosynthesis Equation Carbon dioxide In the presence of chlorophyll water glucose Light energy oxygen By-product Raw materials Food product

9 The Green Leaf

10 Photosynthesis Practical Activities You are going to set up the two practicals below using a destarched geranium plant Comparing photosynthesis in light and dark conditions (pg84-86) Comparing photosynthesis in the presence and absence of carbon dioxide (pg87-89) After 48 hours you are going to test all four leaves for starch

11 COMPARING PHOTOSYNTHESIS TESTING A LEAF FOR STARCH

12 Testing a leaf for starch You are going to test 6 leaf discs for starch 1. Without light 2. With light 3. Without carbon dioxide 4. With carbon dioxide 5. Without chlorophyll 6. With chlorophyll Before you begin design a results table

13 Testing a leaf for starch 1. Cut out a leaf disc using a cork borer 2. Boil the leaf disc in a beaker of water for 1 minute 3. Turn off the Bunsen burner 4. Boil the leaf disc in ethanol for 5 minutes 5. Remove from ethanol 6. Wash leaf disc in warm water 7. Test leaf disc for starch using iodine and a dimple tray

14 Making Conclusions Write a paragraph on your results for each leaf disc How does this provide evidence for photosynthesis

15 Evaluating method What were the possible sources of error, how were they minimised? When testing a leaf for starch why was it necessary to: Immerse the disc in boiling water for one minute Immerse the disc in boiling alcohol for several minutes Rinse the disc in warm water for a few seconds

16 Practice Question Applying your knowledge Question 5 Draw a diagram of figure 5.16 Answer the questions in full sentences

17 BIOCHEMISTRY OF PHOTOSYNTHESIS

18 Learning Objectives Energy Fixation Explain the importance of diffusion to the photosynthetic process. Describe photosynthesis as a set of two summary equations; photolysis followed by carbon fixation (describe each stage, raw materials and products of each). State that glucose is converted to other carbohydrates (storage and structural) and give an example of each.

19 Biochemistry of Photosynthesis Photosynthesis has two stages Light-dependent stage Photolysis Temperature-dependent stage Carbon fixation

20 Photolysis light energy is used to split water molecules into Hydrogen Combines with a hydrogen acceptor Oxygen Is released as a by-product ATP is regenerated photophosphorylation

21 The reduced hydrogen acceptor and ATP are essential for the second stage in photosynthesis, carbon fixation.

22 Carbon Fixation A cyclic series of enzyme controlled reactions Carbon dioxide is combined with hydrogen to form the carbohydrate glucose.

23 Synthesis of complex carbohydrates Glucose molecules can become linked in long chains, which coil up to form starch grains this is used for storage Glucose molecules can become linked in long chains of cellulose molecules which form fibres this is a structural carbohydrate

24 Learning Objectives Factors limiting the rate of photosynthesis Name factors that can limit the rate of photosynthesis. Describe horticultural methods of producing early crops.

25 Factors affecting photosynthesis Environmental factors which affect the rate of photosynthesis includes Light intensity Carbon dioxide concentration temperature

26 Measuring photosynthesis Rate of photosynthesis can be estimated by measuring Evolution of oxygen per unit time Uptake of carbon dioxide per unit time Production of carbohydrate (as an increase in dry mass) per unit time

27 Investigating the rate of photosynthesis

28 Limiting Factors The factors that is in its shortest supply will be the factor that limits the rate of photosynthesis

29 Limiting Factors

30 Variation in light intensity at one CO 2 concentration

31 Variation in CO 2 concentration at one light intensity

32 Variation in CO 2 concentration at two light intensities

33 Investigating the effect of varying temperature The rate of photosynthesis will increase to an optimum temperature Beyond optimum, photosynthetic rate decreases rapidly The enzymes that control the reactions are denatured by high temperatures

34 Effect of temperature on the rate of photosynthesis

35 Early crops in horticulture If there is a factor limiting the rate of photosynthesis in a greenhouse, the factors that can be controlled include Temperature Light intensity Carbon dioxide concentration