Think about… 21.1 Basic concepts of photosynthesis 21.2 Requirements for photosynthesis

2. Think about… 21.1 Basic concepts of photosynthesis 21.2 Requirements for photosynthesis 21.3 Site of photosynthesis 21.4 The process of photosynthesis 21.5 The fate of photosynthetic products 21.6 Factors affecting the rate of photosynthesis Recall ‘Think about…’ Summary concept map

3. Growing crops in greenhouses A greenhouse (溫室) is a transparent building made for growing plants under controlled conditions.

4. Growing crops in greenhouses The conditions promote photosynthesis to enhance plant growth.

5. Growing crops in greenhouses Crops like green peppers and tomatoes are not suitable to grow in Hong Kong.

6. Growing crops in greenhouses With greenhouses, farmers can grow them all year round.

7. 1 What conditions of a greenhouse promote photosynthesis

8. 2 How do plants make food by photosynthesis

9. 3 What is the significance of photosynthesis to the ecosystem

10. 21.1 Basic concepts of photosynthesis What is photosynthesis?

11. 21.1 Basic concepts of photosynthesis What is photosynthesis? • the process by which organic substances are made from simple inorganic substances using light energy • an anabolic process chemical energy light energy plants / algae

12. 21.1 Basic concepts of photosynthesis What is photosynthesis? • occurs in chloroplasts • overall equation: light absorbed glucose CO2 water O2 by chlorophyll by-product

13. 21.1 Basic concepts of photosynthesis What is photosynthesis? • plants make their own food by photosynthesis light photosynthesis CO2 minerals water inorganic nutrients

14. 21.1 Basic concepts of photosynthesis What is photosynthesis? organic nutrients carbohydrates photosynthesis lipids proteins plant materials

15. 21.1 Basic concepts of photosynthesis What is the significance of photosynthesis?

16. 21.1 Basic concepts of photosynthesis 1 Maintaining energy flow in ecosystem light energy photosynthesis green plants chemical energy in feeding consumers chemical energy in

17. 21.1 Basic concepts of photosynthesis 2 Providing the basic food source • most organisms depend on plants directly or indirectly for food human plant cow producer

18. 21.1 Basic concepts of photosynthesis 3 Maintaining oxygen and carbon dioxide balance burning of fuels respiration release CO2 consume O2

19. 21.1 Basic concepts of photosynthesis 3 Maintaining oxygen and carbon dioxide balance • oxygen consumed is replaced by that released by plantsduring photosynthesis • plantstake in carbon dioxide for photosynthesis

20. 21.1 Basic concepts of photosynthesis 1 Photosynthesis is the process by which substances are made from simple inorganic substances using energy. organic light

21. 21.1 Basic concepts of photosynthesis 1 In plants, is made from carbon dioxide and water during photosynthesis. is released as a by-product. glucose Oxygen

22. 21.1 Basic concepts of photosynthesis 2 Photosynthesis occurs in the . there absorbs light energy to drive the photosynthetic reactions. chloroplasts Chlorophyll

23. 21.1 Basic concepts of photosynthesis 3 During photosynthesis, light energy from the sun is captured by plants, and converted to energy stored in the organic substances produced. Photosynthesis maintains chemical the in the ecosystem. energy flow

24. 21.1 Basic concepts of photosynthesis 3 It provides the basic for most organisms. food source It maintains the balance of atmospheric and carbon dioxide. oxygen

25. 21.2 Requirements for photosynthesis How do we know if photosynthesis has occurred?

26. 21.2 Requirements for photosynthesis Has photosynthesis occurred? glucose formed in photosynthesis starch quick conversion • test for the presence of starch to find out if photosynthesis has occurred

27. 21.2 Requirements for photosynthesis Has photosynthesis occurred? • starch formed before affects the results destarching (脫澱粉) keep in darkness for 24 hrs

28. 21.2 Requirements for photosynthesis 21.1 Video Detection of starch produced from photosynthesis (the iodine test) 1 Boil a leaf in water for a minute. leaf boiling water

29. 21.2 Requirements for photosynthesis 21.1 Detection of starch produced from photosynthesis (the iodine test) 2 Turn off the Bunsen burner. Transfer the leaf to a boiling tube half filled with absolute alcohol. Put the tube into a beaker of hot water. alcohol hot water

30. 21.2 Requirements for photosynthesis 21.1 Detection of starch produced from photosynthesis (the iodine test) 3 When the leaf has lost its green colour, i.e. decolourized, transfer it from the tube to hot water. hot water

31. 21.2 Requirements for photosynthesis 21.1 Detection of starch produced from photosynthesis (the iodine test) iodine 4 Spread the leaf on a white tile. Add a few drops of iodine solution onto its surface. Observe any colour change in the leaf. decolourized leaf white tile

32. 21.2 Requirements for photosynthesis 21.1 Results and discussion The iodine solution turns blue-black all over the leaf. This result indicates that starch is present in the whole leaf.

33. 21.2 Requirements for photosynthesis Has photosynthesis occurred? • oxygen is a by-product of photosynthesis • test for oxygen using a glowing splint test tube if oxygen is present, glowing splint relights

34. 21.2 Requirements for photosynthesis 21.2 Detection of oxygen produced from photosynthesis 1 Put a few Hydrilla plants in a beaker of dilute sodium hydrogencarbonate solution. dilute sodium hydrogen- carbonate solution Hydrilla

35. 21.2 Requirements for photosynthesis 21.2 Detection of oxygen produced from photosynthesis filter funnel 2 Put an inverted filter funnel on three stoppers to cover the plants. Put a test tube completely filled with dilute sodium hydrogencarbonate solution on top of the funnel. stopper

36. 21.2 Requirements for photosynthesis 21.2 Detection of oxygen produced from photosynthesis 3 Leave the set-up in bright light for at least one day.

37. 21.2 Requirements for photosynthesis 21.2 Detection of oxygen produced from photosynthesis 4 Remove the test tube carefully so that the gas cannot escape. Put a glowing splint over the mouth of the test tube to test for oxygen.

38. 21.2 Requirements for photosynthesis 21.2 Results and discussion The glowing splint relights. This result shows that the gas released from Hydrilla is oxygen.

39. 21.2 Requirements for photosynthesis Requirements for photosynthesis • two set-ups in the investigation - experimental set-up: the factor being tested is present - control set-up: the factor is absent

40. 21.2 Requirements for photosynthesis Requirements for photosynthesis 1 Chlorophyll • impossible to remove chlorophyll from a leaf without killing it use plants with variegated leaves (斑葉)

41. 21.2 Requirements for photosynthesis Requirements for photosynthesis 1 Chlorophyll green part (chlorophyll present) Coleus

42. 21.2 Requirements for photosynthesis Requirements for photosynthesis 1 Chlorophyll green part non-green part (chlorophyll present) (chlorophyll absent) Coleus

43. 21.2 Requirements for photosynthesis 21.3 Simulation Video Investigation of the need for chlorophyll in photosynthesis variegated leaf 1 Destarch a variegated plant by putting it the dark for at least 24 hours. Pick a leaf and test it for starch. dark environment

44. 21.2 Requirements for photosynthesis 21.3 Investigation of the need for chlorophyll in photosynthesis 2 Expose the whole plant to bright light for about 5 hours. 3 Pick a leaf. Draw a sketch of it to show the colour pattern. 4 Test the leaf for starch. Draw another sketch of it to show the result of the iodine test.

45. 21.2 Requirements for photosynthesis 21.3 Results and discussion Starch is present only in the green parts which contains chlorophyll. There is no or little starch in the non-green parts where chlorophyll is absent. These results show that chlorophyll is required for photosynthesis. In this practical, the non-green parts of the leaf serve as the control.

46. 21.2 Requirements for photosynthesis Requirements for photosynthesis 2 Carbon dioxide • put a leaf of a destarched plant in a condition without carbon dioxide • put another leaf in normal atmosphere • use potassiumhydroxide to remove carbon dioxide

47. 21.2 Requirements for photosynthesis 21.4 Simulation Investigation of the need for carbon dioxide in photosynthesis 1 Destarch a plant by putting it in the dark for at least 24 hours. Pick a leaf and test it for starch.

48. 21.2 Requirements for photosynthesis 21.4 Investigation of the need for carbon dioxide in photosynthesis 2 Set up the apparatus as shown. split cork or cotton wool conical flask potassium hydroxide pellet leaf A leaf B potted plant

49. 21.2 Requirements for photosynthesis 21.4 Investigation of the need for carbon dioxide in photosynthesis 3 Expose the whole plant to bright light for about 5 hours. 4 Test leaves A and B for starch.

50. 21.2 Requirements for photosynthesis 21.4 Results and discussion Starch is present in leaf A but absent in leaf B. As leaf B is exposed to air without carbon dioxide, the results show that carbon dioxide is required for photosynthesis. In this practical, leaf B serves as the control.