WOW!!! What a pretty flower!!!!!

2. YUMMY!!! Sigh, I wish it’s time for dinner already. I am so hungry! Hmmm, I wonder what we are having tonight!?

3. WOW!!! What a pretty flower!!!!!

4. Hey! I wonder if plants need to eat too!? If they do, then how do they get their food?

5. Of course we eat!!! And we are able to make our own food. That is why we are called AUTOTROPHS! Hmmm, I thought you learned all about this already!!! Do you remember how we can make our own food???

6. Things needed: Light Carbon dioxide Water Chlorophyll Things produced: • Carbohydrates (which can be used to form fats and proteins) • Oxygen

7. Photosynthesis • As one can see, plants need to obtain carbon dioxide in order to carry out photosynthesis • They also release oxygen as a by-product • The process by which plants exchange oxygen and carbon dioxide is called ___________ gas exchange

8. Gas Exchange • Plants exchange gases by diffusion • Where does gas exchange occur in plants?

9. Internal Structure of Leaf

10. Gas Exchange • Gas exchange mainly occurs in the leaves • How do gases diffuse into and out of the leaves?

12. Stomata

13. Stomata

14. Gas Exchange • Gas exchange can also take place in the stems and roots • Herbaceous plants – diffusion through stomata on stem surface • Woody plants - stomata when young - lenticels when matured

15. Lenticels • Gases cannot penetrate the protective cork layer • Lenticels are loosely-packed masses of cells in the bark of a woody plant, visible on the surface of a stem as raised spots, through which gas exchange occurs

16. Lenticels

17. Lenticels

18. Gas Exchange in Roots • The epidermis is usually just one cell thick. Root epidermal cells lack a thick cuticle which would interfere with water uptake. Moreover, there is no stomata present as the cell membrane is very thin and therefore gases can directly diffuse into and out of the cells

19. Adaptation of Leaves to Photosynthesis

20. Adaptation of Leaves The leaf is thin Decreases diffusion distance for gases

21. Adaptation of Leaves Numerous stomata on lower epidermis Allows rapid gaseous exchange with the atmosphere

22. Adaptation of Leaves Guard cells control the size of stomata In presence of light, stomata open widely to allow the diffusion of carbon dioxide and oxygen

23. Guard Cells • When turgor develops within the two guard cells, the outer walls bulge out and force the inner walls into a crescent shape. This opens the stomata. When the guard cells lose turgor, the elastic inner walls regain their original shape and the stomata closes

24. Adaptation of Leaves Spongy mesophyll cells are loosely packed with numerous large air spaces Allows rapid diffusion and free circulation of gases throughout the leaf

25. Adaptation of Leaves Most cells in the leaves are surrounded by a layer of water Allows gases to dissolve and diffuse into and out of the cells

26. Gas Exchange Carbon Dioxide Oxygen Carbon Dioxide Oxygen Respiration Photosynthesis

27. What will be the net gas exchange between the leaf and its surrounding air?

28. Rate of Gas Exchange The rate of gas exchange is different throughout the day due to a change in light intensity

29. What is going on here?

30. Light Intensity • Night – plants carry out RESPIRATION and release CARBON DIOXIDE

31. Light Intensity

32. Light Intensity • Night – plants carry out RESPIRATION and release CARBON DIOXIDE • Early morning – PHOTOSYNTHESIS begins to take place as light intensity increases Rate of photosynthesis < Rate of respiration Net release of CARBON DIOXIDE

33. Light Intensity

34. Light Intensity • Around 6:00 a.m. – light intensity increases even more Rate of photosynthesis = Rate of respiration Release of CO2 = Uptake of CO2 That is, there is NO net gas exchange This is referred to as the COMPENSATION POINT

35. Light Intensity

36. Light Intensity • Afternoon – light intensity further increases Rate of photosynthesis > Rate of respiration Net uptake of CARBON DIOXIDE Net uptake of carbon dioxide reaches a maximum in early afternoon

37. Light Intensity

38. Light Intensity • Evening – light intensity begins to decrease At a certain time period, there will again be a net release of CARBON DIOXIDE when plants only carry out RESPIRATION at night

39. Light Intensity

40. Similarly, we can study the relationship between light intensity and the exchange of OXYGEN

41. Critical Thinking 8.1 (p. 11) Question 1. Does a plant release or absorb oxygen at night? Ans: A plant absorbs oxygen at night

42. Critical Thinking 8.1 (p. 11) Question 2. When the light intensity gradually increases in the morning, will there be any changes in the exchange of oxygen? Why? Ans: The rate of oxygen uptake would gradually decrease and the rate of oxygen release would gradually increase. It is because photosynthesis begins to occur when light intensity gradually increases in the morning

43. Critical Thinking 8.1 (p. 11) Questions 3. Why is there a compensation point? Ans: Compensation point refers to the light intensity at which there is no net gas exchange 4. What will happen to the exchange of oxygen when the light intensity further increases? Ans: The rate of oxygen release would increase as light intensity increases

44. Critical Thinking 8.1 (p. 11) Question 5. Draw a graph to show the relationship between light intensity and the exchange of oxygen of a plant.

45. Critical Thinking 8.1 (p. 11)

46. INVESTIGATION #1 Studying the effect of light intensity on gas exchange in leaves using hydrogencarbonate indicator

47. Introduction to Investigation • In this investigation, you will study the effect of light intensity on gas exchange in leaves • Green leaves will be put into different light intensities, and the level of carbon dioxide will be estimated by using hydrogencarbonate indicator solution • Note: Increase in CO2 – Orange to Yellow Decrease in CO2 – Orange to Purple

48. A B C D Procedure Please refer to pages 7 and 8 in your textbook

49. Results Table

50. INVESTIGATION #2 Studying the effect of light intensity on the gas exchange of a plant using a data logger