1. The Mysterious Tree

2. Jan Baptist van Helmont (1577 – 1644)
Belgian physician

3. During his time, people believed that plants obtain food from the soil.
He conducted an investigation to determine where the plants get their mass.

4. His Investigation 2kg 90kg
2kg
90kg

5. His Findings
2kg
90kg
76kg
90kg

6. His Conclusion
Since the mass of the soil remained the same, the gain in mass of the willow tree had come from water. +

7. Question
What are the independent and dependent variables in this investigation?
Independent
- Time
Dependent
- Mass of soil
- Mass of tree

8. Question
Carbon-rich organic molecules such as carbohydrates are found in plants. These molecules are also energy-rich. However, water does not provide carbon. What are some of the factors Helmont failed to take into account?
Not taken into account:
Carbon dioxide
Sunlight

9. Question
Suggest another hypothesis which could explain why the mass of the tree increased but the mass of the soil remained constant.
Suggested answer: The growth of the tree is dependent on water, carbon dioxide and sunlight.

10. Ask yourself…
If sunlight and carbon dioxide are the sources of energy and carbon for making carbon-rich organic molecules:
1. How is the carbon dioxide converted into these organic molecules?
2. How is the energy in sunlight being transformed into chemical energy stored in carbohydrate molecules?

11. The Mysterious Tree
Since then, scientists have found that plants produce food in a process known as Photosynthesis.
(Greek: photos = light; synthesis = putting together)

12. So, what is Photosynthesis?
So, what is Photosynthesis?

14. Photosynthesis is…
The process by which plants use carbon dioxide, water and light trapped by chlorophyll to make food in the form of glucose, with oxygen being given off during the process. + +

15. Photosynthesis The process in word equation… Glucose Carbon dioxide
Light +
Water +
chlorophyll
Oxygen

16. Where does photosynthesis occur?
Photosynthesis take place in chloroplasts

17. What are chloroplasts?
Disc-like structures found in plant cells

18. Question
In which part of the plant cell are you able to find chloroplasts?
Answer: Cytoplasm

19. Question
Why are plants green?

20. Why are plants green?
Chloroplasts have green pigments called chlorophyll to trap sunlight.
Chlorophyll
Absorb mostly red & blue
Reflect or transmit green

22. What does the absorption spectra graph tell you about the rate of photosynthesis at the blue and red wavelengths?
Answer: blue and red wavelengths indicate the highest rate of photosynthesis

23. What would happen if only green light reached the earth?
Answer:
- Amount of Oxygen gas produced will decrease.
- Amount of glucose produced will decrease, affecting the food chain.

24. Photosynthesis – A Short Summary
During photosynthesis, light energy is absorbed by chlorophyll and transformed into chemical energy.
The chemical energy is used in the synthesis of glucose from carbon dioxide and water.
Oxygen is given off during the process.
Light energy
chemical energy
chlorophyll

25. Photosynthesis – A Short Summary
The process in word equation…
Glucose
Carbon
dioxide
Light +
Water +
chlorophyll
Oxygen

26. Glucose
Glucose is a simple sugar used to provide food for the plant and to make proteins, fats, and cellulose cell walls.
Excess glucose produced is stored in the form of starch in leaves and storage organs such as storage stems.

27. Oxygen Oxygen gas is given off during photosynthesis.

28. Oxygen Oxygen is used by the plant cells for aerobic respiration.
Excess oxygen is removed by the plant to the surroundings.

29. How do plants take in carbon dioxide and remove oxygen?
Carbon dioxide diffuses into the plant through the stomata.
Excess oxygen leaves the plant through the stomata by diffusion.

30. Occurs in pairs on the underside of a leaf
Each pair is shaped so that a tiny opening called stoma (plural: stomata) exists between them
Stomata allows for gaseous exchange between the leaf and the surroundings, and water to escape
The opening and closing of the stomata is caused by the guard cells changing in shape
Guard cell

31. How do we study photosynthesis?
If photosynthesis has taken place, glucose will be formed. Excess glucose produced is stored in the form of starch.
The presence of starch in leaves shows that photosynthesis has taken place.
Test for starch using the iodine test.

32. Iodine Test Iodine solution turns blue-black in the presence of starch
Iodine solution (yellowish brown)

33. Iodine Test - Procedure
Put plant in darkness for a few days
Expose plant to sunlight for a few hours
Remove a green leaf from the plant
Put leaf in boiling water for a few minutes
Put boiled leaf in boiling tube containing ethanol. Place boiling tube in hot water bath.
Remove leaf from boiling tube. Place leaf in hot water to soften it
Remove leaf from water
Add a few drops of iodine solution to the leaf.

34. Questions What is the purpose of putting the leaf in boiling water
– to stop all chemical reactions taking place in the leaf
What is the purpose of ethanol?
– to remove chlorophyll

35. Questions What happened to the leaf after 10 minutes in ethanol?
What is the colour of the ethanol
(a) before the leaf is placed inside
(b) 10 minutes after the leaf is placed inside
Colourless
Green
What happened to the leaf after 10 minutes in ethanol?
– decolourised

36. Is sunlight necessary for starch formation?
Experiment shows that sunlight is essential for starch formation.
a) Plant kept in the dark
b) Plant kept in the light
leaf turns light brown
leaf turns blue-black

37. Is carbon dioxide necessary for starch formation?
How would you test it out?
Grow a potted plant in a bell-jar in the absence of carbon dioxide.
Absorb carbon dioxide from the air in the jar using sodium or potassium hydroxide solution.
Do a comparison with a plant grown in normal air containing carbon dioxide.

38. Is carbon dioxide necessary for starch formation?
Conclusion: starch is formed when plant is supplied with carbon dioxide.
a) Plant grown in air without carbon dioxide
b) Plant grown in air with carbon dioxide
Sodium or potassium hydroxide
Water

39. An alternative…

40. Is chlorophyll necessary for starch formation?
For this investigation, variegated leaves are required. In a variegated leaf, some parts are green and some parts are without chlorophyll.

41. Is chlorophyll necessary for starch formation?
Step 1: Destarch a plant with variegated leaves by placing it in the dark for 2 days.
Step 2: Expose plant to strong sunlight for a few hours.
Step 3: Remove a variegated leaf.
Step 4: Make a drawing of the leaf to show the distribution of chlorophyll.
Step 5: Test the leaf for starch.

42. Is chlorophyll necessary for starch formation?
Conclusion: starch is formed in those parts of the leaf that contain chlorophyll.
a) A variegated leaf
b) A variegated leaf tested for starch

43. Conditions essential for photosynthesis
Sunlight (light energy)
Light energy is converted to chemical energy stored in glucose.
Suitable temperature
Photosynthesis depends on the reactions of enzymes in the chloroplasts. Enzyme reactions are fastest at a suitable temperature.
Chlorophyll
This green pigment absorbs light energy and changes it into chemical energy needed to manufacture glucose.
glucose
Carbon dioxide and water
These are the raw materials needed to form carbohydrates (glucose).
water

44. Testing for gases
When carbon dioxide gas is bubbled through limewater, a white precipitate will be formed in the limewater
Oxygen gas will relight a glowing splint

45. Importance of photosynthesis
Why is photosynthesis important?
- Photosynthesis makes chemical energy available to animals
- Photosynthesis removes carbon dioxide and provides oxygen.

46. Photosynthesis makes chemical energy available to animals
Food Chain

47. Photosynthesis makes chemical energy available to animals
Plants provide organisms with food and energy to live directly or indirectly
Plants are the primary food source because they produce their own food.
Thus, plants are called producers.
Animals are called consumers.

48. Photosynthesis removes carbon dioxide and provides oxygen.
Photosynthesis removes carbon dioxide from the air.
Oxygen produced by plants is used by living organisms in respiration.

49. http://jrscience. wcp. muohio