The document summarizes an experiment on photosynthesis. [1] Van Helmont planted a willow sapling and measured the soil weight before and after 5 years, finding only a small loss of 52g of soil. [2] However, the tree had gained 74kg, showing that the soil is not the main source of a plant's growth materials. [3] Photosynthesis converts carbon dioxide, water, and sunlight into glucose and oxygen using chlorophyll in the leaves.

2. What do you conclude?
90.72kg 90.20kg
soil soil
In the 17th Century, A Belgian physician, van Helmont, set up an
experiment in which he planted a willow sapling in a weighed
amount of soil.
The soil was watered but nothing else was added. After 5
years, the tree had gained 74kg in weight but the soil had lost
only 52g.
The soil is not providing the plant with
materials for growth.

3. Photosynthesis
 is the build up of sugars from carbon dioxide
and water by green plants using energy from
sunlight by means of chlorophyll

4. Balanced Equation:
sunlight
6CO2 6H 2O chlorophyll
C6 H12O6 6O2
Word Equation:
sunlight
carbon dioxide + water chlorophyll
glucose + oxygen

5. Explain the results of each experiment.
Candle burning in an A mouse dies when A mouse lives if a
airtight jar went out. kept in an airtight jar. plant is placed inside
an airtight jar.

6. Site of Photosynthesis:
 any green part of the plant, but mostly the
leaves

7.  the whole process of photosynthesis takes
place inside chloroplasts

8. Name the pigment inside chloroplasts
Function of chlorophyll is to……………............

9. Name two gases that diffuse out of
the leaf during the day
stoma
1. Water vapour
2. O2

10. Adaptations of leaves for photosynthesis
1) Broad, flat shape:
 a large surface area to
absorb light & CO2.
2) Thin leaves:
 diffusion of gases is
fast.
3) Large air spaces:
 quick diffusion of
gases.

11. 4) Numerous stomata:
 allow exchange of gases.
5) Many chloroplasts in palisade
cells:
 to absorb light.
6) The branching veins:
 provide a good supply of
water to the
photosynthesising cells.

12. Question: SEP, 2011
In a long-term investigation on
photosynthesis, plant scientists observed that
plants growing in reduced atmospheric carbon
dioxide (amount of carbon dioxide is less than that
found in air) responded by developing greater
number of stomata per unit leaf area.
List TWO features of the leaf that affect the rate of
photosynthesis. (2)
1. Surface area
2. Number of stomata per unit area
3. Amount of chloroplasts

13. Explain why plants growing in conditions of
reduced carbon dioxide levels have an
increased number of stomata per unit area. (4)
Stomata open to allow CO2 to enter the leaf for
photosynthesis.
An increase in the number of stomata means
that more CO2 enters. This makes up for the
reduced CO2.

15. Experiments to study:
sunlight
6CO2 6H 2O chlorophyll
C6 H12O6 6O2
1. Is chlorophyll is necessary for
photosynthesis?
2. Is light necessary for photosynthesis?
3. Is CO2 necessary for photosynthesis?
4. Is O2 produced during photosynthesis?

16. Leaves used in these experiments MUST
NOT contain starch at the start. Why?
1. Is chlorophyll is necessary for
photosynthesis?
2. Is light necessary for photosynthesis?
3. Is CO2 necessary for photosynthesis?
So that one can tell whether it has
formed during the experiment.

17. These 3 experiments :
1. Is chlorophyll is necessary for
photosynthesis?
2. Is light necessary for photosynthesis?
3. Is CO2 necessary for photosynthesis?
…………involve:
1. Destarching the plant
2. Testing a leaf for starch

18. What is a ‘destarched’ plant?
 A plant without starch
Starch in
cells.
No starch
in cells.

19. How is a plant destarched?
 by leaving it in the dark for 2-3 days
What happens to the
starch in the dark?

20. How can you tell whether
photosynthesis has occurred or not?
By testing for starch using iodine solution.
No starch Has starch

21. Can you test a leaf for starch by
pouring iodine solution onto a leaf?
NO. Iodine solution runs off the leaf
surface due to the waxy cuticle.

22. 4 steps in testing a leaf for starch
Boil leaf
1 Dip leaf in boiling
water for 30 seconds.
2 in alcohol.
Spread leaf on a white tile
Dip leaf in boiling 4 and place iodine solution
3 water. on the leaf.

23. Boiling in alcohol removes chlorophyll
Precaution: Switch off bunsen burner.

24. Why is a white tile used?
Colour changes are seen better on a
white background.

26. 1. Plant with variegated leaves is destarched.
2. Left in sunlight for 2-3 hours.
3. Outline of leaf is drawn.
4. Leaf is tested for starch using those 4 steps
explained previously.
CONTROL

27. Result & Conclusion
Yellow: no starch
Blue black: has starch
Chlorophyll is needed for photosynthesis.

30. 1. Plant is destarched.
2. A black paper is placed on one of the leaves.
3. Plant is left in sunlight for 2-3 hours.
4. Leaf is tested for starch using those 4 steps
explained previously.
CONTROL

31. Result & Conclusion
Blue black: has starch
Yellow: no starch
Light is needed for photosynthesis.

33. 1. Two plants are destarched.
2. The plants are watered and set up as shown.
3. Plants are left in sunlight for 2-3 hours.
4. A leaf from each plant is tested for starch.
CONTROL

34. What is the function of:
Soda lime Sodium hydrogen
[sodium hydroxide] carbonate
Absorbs CO2 Releases CO2
- CO2 + CO2

35. Result & Conclusion
- CO2 + CO2
Yellow: Blue black:
no starch has starch
CO2 is needed for photosynthesis.

37. Canadian
pondweed
(Elodea
canadensis)

38. 1. The funnel is raised to allow water to circulate.
2. A control is set up and placed in the dark.
3. When enough gas is collected, the test tube is
removed and a glowing splint inserted to test
for oxygen.

40. Test for O2:
Relights a
glowing splint

41. Result
Glowing
splint
relighted.
Conclusion
Gas collected was
rich in O2.

43. Count number of bubbles released in
1 minute

44. What does the graph
show?

46. When do plants respire?
All the time.

47. Gaseous exchange in plants
DARKNESS DIM LIGHT BRIGHT LIGHT
O2
Respiration
CO2

48. Ann has many plants in her room. Explain
why she wakes up feeling dizzy.
Plants use up O2 at
night.
Not enough O2 for
Ann.

49. Gaseous exchange in plants
DARKNESS DIM LIGHT BRIGHT LIGHT
O2
O2
Photosynthesis
Respiration
CO2 Respiration
CO2

50. Gaseous exchange in plants
DARKNESS DIM LIGHT BRIGHT LIGHT
O2
O2
Photosynthesis Photosynthesis
Respiration CO2
O2
CO2 Respiration Respiration
Rates are equal. CO2

52. Compensation point
Rate of photosynthesis = Rate of respiration
sunlight
6CO2 6H 2O chlorophyll
C6 H12O6 6O2
C6 H12O6 6O2 6CO2 6 H 2O energy

53. When is compensation point reached
in nature?
Dawn / dusk

54. Finding the compensation point

56. According to formula, what is needed
for photosynthesis?
sunlight
6CO2 6H 2O chlorophyll
C6 H12O6 6O2
+ Temperature
A limiting factor is the factor in
shortest supply.

57. The limiting factors are:
Light
Temp. CO2
PHOTOSYNTHESIS
Chlorophyll H2O

58. Effect of light intensity on the rate of
photosynthesis - temperature & CO2
were kept constant

59. Question: SEP, 2010
Give a biological explanation for each of the
following statements.
It is possible to grow plants in a closed glass bottle
but a goldfish bowl must be open to air for the
goldfish to survive. (4)
Oxygen from air
diffuses into water.
Plants release O2 during Fish thus can respire.
the day which is used
for respiration all the
time. Respiration
releases CO2 which is
used for photosynthesis
by day.

60. What is the limiting factor between A-B?
CO2

61. Why is the rate higher at 25 C?
Enzymes work faster.
Rate of
photosynthesis
25 C
10 C
CO2 concentration

63. The glucose formed:
 is rapidly changed into STARCH to be stored
for a short period in the leaf
SUCROSE
carried in phloem
both up & down

64. other sugars fruits
energy
e.g. seed germination protein
GLUCOSE
starch cytoplasm
cellulose
cell walls
storage e.g. starch in potato

65. Glucose (C6H12O6) is used to form
proteins, but three other elements
are needed. Name the elements.
 nitrogen
 sulfur
 phosphorus

67. Mineral ions are absorbed
 from the soil in the form of
salts
 e.g. a plant absorbs potassium
nitrate (KNO3) to use potassium
and nitrogen

68. Sources of mineral ions
1. Rock erosion 1. Fertilisers

69. Salts are lost from the soil:
1. absorption by plants 2. leaching

70. Element & Use in plant Effect of
Source deficiency
Nitrogen: To form proteins Lack of growth
nitrates +
ammonia
Sulfur: To form certain Yellowing of
sulfates amino acids & so young leaves
proteins

71. Element & Use in plant Effect of
Source deficiency
Magnesium: Forms the centre of Yellowing of
as salt in chlorophyll older leaves
fertiliser molecules
Iron: fertiliser Essential for Yellowing of
salt chlorophyll young leaves
formation

75. Question: MAY, 2011
Give a biological explanation for each of the
following statements.
The process of photosynthesis is vital for all
living things. (6)

76. Photosynthesis is important not only to green plants but
to all living organisms. It is the basic reaction that brings
the energy of the sun into ecosystems. 1 mark
The flow of energy in ecosystems is one way so there is a
constant need for replenishment from the energy source
and therefore a constant need for photosynthesis.
2 marks
Photosynthesis is important for the formation of
biomass – this acts as a food reservoir for herbivores. 1
mark
Photosynthesis is also essential for maintaining a
constant level of oxygen and carbon dioxide. The oxygen
given off is available for respiration while the carbon
dioxide is used for photosynthesis. This prevents the
level of carbon dioxide from rising. 2 marks

77. Question: MAY, 2012
Comment on the biological significance of each of
the following statements.
It is advantageous for a farmer to grow crops such
as celery, lettuce and tomatoes in glasshouses. (6)

78.  Keep off frost and extremely wet conditions
in winter
 Shield plants from wind
 Keeps a warm temperature – higher rate of
photosynthesis
 Prevents excessive water loss
 Protect from pests
 Lights can be left on – plants
photosynthesise during the night

79. Question: MAY, 2006
The following diagram shows lettuce under cloches.
Cloches are movable tent-like covers of transparent
polythene (plastic) which farmers put over soil and
plants, in open fields.
Suggest TWO advantages that cloches have over
glasshouses. (2)
1. Cheaper to set up and maintain
2. Can be easily removed
3. Need fewer people to look
after them

81. YES

82. Plants are grown in a salt solution
rather than soil

83. Advantages of growing
plants without soil:
1. Less water used

84. Advantages of growing plants without
soil
2. No pests

85. Kew Gardens, London