2. Review Question Which mode of nutrition do the green plants carry out?
A. Autotrophic nutrition
B. Heterotrophic nutrition

3. Sorry! You’re wrong!
Heterotrophic nutrition is the mode of nutrition in which organisms have to depend on other organisms or dead organic matters as their food sources. Green plants, however, can make organic food by themselves using simple inorganic substances.

4. Very Good! Photosynthesis
Autotrophic nutrition is the mode of nutrition in which organisms can make organic food by themselves using simple inorganic substances.
The process by which the green plants obtain nutrients is called :
Photosynthesis

5. Nature of photosynthesis
Occurs in Chloroplast
Necessary factors :
Carbon dioxide
Water
Sunlight
Chlorophyll

6. Experiments on photosynthesis

7. Destarching – removing starch
Reason:
To show that any starch found after the experiment is produced during the period of investigation
Method:
By placing the plant in dark for for 2 days

8. To test a leaf for the presence of Starch
Investigation 8.1
To test a leaf for the presence of Starch

9. Why is the leaf first boiled in water ?
boiling water
turn off Bunsen burner
boiling alcohol
hot water
iodine
white tile
Why is the leaf first boiled in water ?
Ans: Because the process can soften the leaf, break down the cuticle and kill the leaf.

10. Why is the leaf then boiled in alcohol ?
boiling water
turn off Bunsen burner
boiling alcohol
hot water
iodine
white tile
Why is the leaf then boiled in alcohol ?
Ans: To decolourize the leaf (to remove chlorophyll).

11. Ans: Because alcohol catches fire easily.
boiling water
turn off Bunsen burner
boiling alcohol
hot water
iodine
white tile
Why is it important to turn off the Bunsen burner when you are heating the alcohol ?
Ans: Because alcohol catches fire easily.

12. Why is the leaf put in hot water after being boiled in alcohol ?
boiling water
turn off Bunsen burner
boiling alcohol
hot water
iodine
white tile
Why is the leaf put in hot water after being boiled in alcohol ?
Ans: To soften the leaf.
(The leaf becomes brittle after boiling in alcohol.)

13. What colour change can be observed if starch is present ?
boiling water
turn off Bunsen burner
boiling alcohol
hot water
iodine
white tile
What colour change can be observed if starch is present ?
Ans: The leaf becomes blue-black when iodine solution is added.

14. To show that Chlorophyll is necessary for Photosynthesis
Investigation 8.3
To show that Chlorophyll is necessary for Photosynthesis

15. Ans: Only the green part.
purple part
Which part of the leaf turns blue-black when treated with iodine solution ?
Ans: Only the green part.

16. Is chlorophyll necessary for photosynthesis ?
green part
purple part
Is chlorophyll necessary for photosynthesis ?
Ans: Yes.

17. What is the control in this experiment ?
green part
purple part
What is the control in this experiment ?
Ans: The green part of the leaf acts as the control.

18. To show that Carbon Dioxide is necessary for Photosynthesis
Investigation 8.4
To show that Carbon Dioxide is necessary for Photosynthesis

19. Why is potassium hydroxide solution put in one of the flasks ?
sunlight B A
water
potassium hydroxide solution
Why is potassium hydroxide solution put in one of the flasks ?
Ans: To absorb all the carbon dioxide in flask B.

20. sunlight B A
water
potassium hydroxide solution
What happens to each leaf after testing the presence of starch at the end of the experiment ?
Ans: The leaf in flask A changes to blue-black while the leaf in flask B stains brown.

21. Ans: Carbon dioxide is necessary for photosynthesis.
sunlight B A
water
potassium hydroxide solution
What do your results suggest about the relationship between carbon dioxide and photosynthesis ?
Ans: Carbon dioxide is necessary for photosynthesis.

22. Summary of Photosynthesis
sunlight
6 CO2 + 6 H20
C6H12O6 + 6 O2
chlorophyll
Carbon Dioxide + water
Glucose + oxygen
(reactants)
(products)
By photosynthesis, green plants convert solar energy into chemical energy stored in glucose

23. Route of Carbon Dioxide for Photosynthesis

24. Chloroplast
Spongy Mesophyll Cell
H2O
Air Space
Stoma
CO2

25. Palisade Mesophyll Cell
Chloroplast
Palisade Mesophyll Cell
H2O
Air Space
Stoma
CO2

26. Mechanism of photosynthesis
A series of enzyme-controlled reactions
Involved in 2 stages:
Light-dependent stage (Light reaction)
Light-independent stage (Dark reaction)

27. Light reaction (Light-dependent stage)
Light is required
Chlorophyll in chloroplast traps Light energy
Light energy absorbed by chlorophyll splits water molecules into hydrogen and oxygen
(photolysis)

28. Oxygen is formed as a by-product & released as a gas through stoma to outside
Hydrogen enters light-independent stage

29. Dark reaction (Light-independent stage)
Light is not required; can take place either in light or darkness
Hydrogen produced in light reaction combines with CO2 to form carbohydrates
Water is formed as a by-product

30. Summary of Photosynthesis
6 CO2 + 6 H20
C6H12O6 + 6 O2
Light
Water
Carbon Dioxide H
Light Reaction
Dark Reaction
Glucose
(C6H12O6)
Oxygen

31. Fate of carbohydrate products in the plant

32. carbon dioxide and water
photosynthesis
carbohydrates (e.g. glucose)
release energy by respiration

33. carbon dioxide and water
photosynthesis
carbohydrates (e.g. glucose)
convert into other products for growth

34. carbon dioxide and water
photosynthesis
carbohydrates (e.g. glucose)
fatty acids
glycerol
combine to form lipids for use or as a food store

35. join together to become protein molecules
carbon dioxide and water
photosynthesis
mineral salts from soil
(e.g. NO3-, SO42-)
carbohydrates (e.g. glucose)
amino acids
join together to become protein molecules

36. carbon dioxide and water photosynthesis
carbohydrates (e.g. glucose)
convert into starch / lipid for storage
Glucose is not a good storage molecule because
Glucose is a soluble substance
it can diffuse out & lost
it affects water potential

37. carbon dioxide and water
photosynthesis
carbohydrates (e.g. glucose)
change into sucrose and is transported to other parts through phloem

38. Factors affecting the rate of photosynthesis

39.  Rate of Photosynthesis
Light Intensity
 Light intensity
 Rate of Photosynthesis

40. Carbon Dioxide Concentration
 Rate of Photosynthesis

41.  Rate of Photosynthesis
Temperature
 Temperature
 Rate of Photosynthesis
Temperature > 40℃
Rate  & Stop soon

42. If no water, stomata close no gaseous exchange photosynthesis ceases
Water Supply
If no water, stomata close
no gaseous exchange
photosynthesis ceases

43. Why is Photosynthesis important ?
Green plants: the only organisms capable of trapping light to manufacture food from simple inorganic substances

44. Why is Photosynthesis important ?
Green plants are producers
It provides food for other organisms & starts the food chain

45. Why is Photosynthesis important ?
Atmospheric carbon dioxide is absorbed & oxygen is released into the atmosphere which maintains the composition of the atmosphere constant

46. Parts of plant where photosynthesis takes place
Mainly in the leaf because
it contains a lot of chloroplasts
it is well adapted for performing photosynthesis

47. Internal Structure of Leaf

48. cuticle
upper epidermis
palisade mesophyll
chloroplasts
spongy mesophyll
intercellular space (air space)
guard cell
lower epidermis
stoma
cuticle

49. Cross-section of a leaf of dicotyledon

50. upper epidermis
protect internal tissues from mechanical damage and bacterial & fungal invasion

51. Cuticle
a waxy layer
prevent water loss from the leaf surface
protect the leaf

52. mesophyll

53. palisade mesophyll (layer)
columnar cells closely packed together
absorb light more efficiently
contains many chloroplasts

54. spongy mesophyll (layer)
irregular cells loosely packed together to leave numerous large air spaces
allow rapid diffusion of gases throughout the leaf
some (fewer than palisade mesophyll) chloroplasts for photosynthesis
spongy mesophyll (layer)

55. same as upper epidermis except the cuticle is thinner
lower epidermis

56. opening which allows gases to pass through it to go into or out of the leaf
stoma (stomata)

57. guard cells
control the size of stoma

58. Stoma
thinner outer wall
Guard cells
thicker inner wall
stoma

59. vascular bundle (vein)

60. Internal Structure of Leaf
xylem
phloem
The .. after a label = the end of labels.

61. xylem to transport water and mineral salts towards the leaf
for mechanical support

62. phloem
to transport organic substances (food/sugar/ glucose/ sucrose) away from the leaf

63. Adaptation of leaf to photosynthesis

64. The leaf is broad & flattened
The leaf is thin
decrease diffusion distance for gases & light
The leaf is broad & flattened
increase surface area to absorb more sunlight

65. Cuticle in upper epidermis is transparent
Allows most light to pass into photosynthetic mesophyll tissues

66. Palisade mesophyll cells are closely packed and contain many chloroplasts
To carry out photosynthesis more efficiently

67. Spongy mesophyll cells are loosely packed with numerous large air spaces
To allow rapid diffusion of gases throughout the leaf

68. Numerous stomata on lower epidermis
To allow rapid gaseous exchange with the atmosphere

69. Extensive vein system
Allow sufficient water to reach the cells in the leaf
To carry food away to other parts of the plant

70. Mineral requirements in plants
In order to synthesize amino acids, nitrate ions which must be taken into the plant from the soil through the root
Other minerals are also necessary to maintain the life of the plant (N, Mg, P, K, S, etc)

71. The importance of nitrogen
For synthesis of proteins, chlorophyll, etc
Taken in form of nitrate ions
Deficiency symptoms:
Little growth ( - no protein made)
Yellowing of leaves ( - no chlorophyll made)

72. The importance of magnesium
Essential component of chlorophyll
Deficiency symptoms:
Yellowing of leaves (no chlorophyll made)
Poor growth (no food manufactured because of lack of chlorophyll)

73. Use of fertilizers in agriculture
Continuous harvesting crops removes valuable mineral salts from soil
Fertilizers are added to replace such loss
Two kinds of fertilizers:
Natural fertilizers
Chemical fertilizers

74. Natural fertilizers From manure (animal waste)
Organic compounds in it are decomposed by the bacteria in soil to form mineral salts

75. Chemical fertilizers
Mainly nitrogenous and phosphorous compounds manufactured artificially

76. Comparison between natural and chemical fertilizers
Natural fertilizers
Chemical fertilizers
Contain humus which can improve soil texture
No humus so cannot improve soil texture
Less soluble in water so less likely to be washed away
Very soluble in water so more likely to be washed away

77. Comparison between natural and chemical fertilizers
Natural fertilizers
Chemical fertilizers
Much cheaper
Very expensive
Less soluble in water so more difficult to be absorbed
Very soluble in water so easier to be absorbed
Time is needed for the decomposition to complete before nutrients are available to plants
More readily to be used by the plants

78. ~ END ~