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Limiting Factors of PhotosynthesisObjectives
• Describe how the rate of photosynthesis can be increased.
• Explain the effects of limiting factors on the rate of photosynthesis.
• Explain why plants take in carbon dioxide and give out oxygen during the day and do the reverse at night.
Key Words limiting factor • respiration
If a car factory can make…
16 engines per week
40 seats per week
58 doors per week
33 windscreens per week … how many finished cars can it make in a week?
The Law of Limiting Factors
When a process depends on two or more factors, the rate of that process is limited by the factor which is in shortest supply
The rate of photosynthesis in a plant can be limited by:
Light intensity Availability of water Availability of carbon dioxide Availability of chlorophyll Temperature
What you need to know:
What factors limit the rate of photosynthesis?
How do we explain why certain factors limit the rate of photosynthesis?
Can we use the law of limiting factors to explain experimental results?
Photosynthesis and the Law of Limiting Factors
Question: What does MRS GREN stand for?
What do the letters below stand for?
M
R
S
G
R
E
N
- movement
- respiration
- sensitivity
- growth
- reproduction
- excretion
- nutrition
Remember: as living things plants are respiring all the time
For plantsNutrition = Photosynthesis
How does the rate of bubbles produced vary as light intensity is increased?
Light Intensity
No.
of B
ubbl
es p
er m
inut
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Light Intensity
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of B
ubbl
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Light IntensityN
o. o
f Bub
bles
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min
ute
Light Intensity
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ubbl
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Light Intensity
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of B
ubbl
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Any oxygen produced by photosynthesis is
used up in respiration
Increasing light intensity increases rate
of bubbling (and photosynthesis)
Increasing light intensity has no effect as rate of photosynthesis is limited availability of carbon
dioxide, water or chlorophyll
Compensation point
Rate of photosynthesis equals rate of
respiration
Complete the questions on the Law of Limiting
Factors and Photosynthesis
worksheet
Question 1:
a. 2 units of glucose can be made by plant A
b. Light is in shortest supply (6 units of light are needed to make one unit of glucose)
c. D (B is limited by the availability of CO2)
d. 4 (it will be limited by the availability of water)
0 1 2 3 4 5 6 7 80
5
10
15
20
25
30
Light Intensity
Num
ber o
f Bub
bles
per
Min
ute
Question 2:
a. Increasing light intensity increases the rate of photosynthesis
b. Increasing light intensity has little to no effect. This is because the rate of photosynthesis is now limited by the availability of CO2/water/temperature
Jan Feb
Marc
hApril
May
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July
August
September
October
November
December
0
5
10
15
20
25
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Amou
nt o
f Car
bon
Dio
xide
in th
e At
mos
pher
e (a
rbitr
ary
units
)
The graph below shows how the amount of CO2 in the atmosphere in the Northern Hemisphere changes through the year
a. Describe the changes seen in the graphb. Suggest a reason for the changes seen in the graph
Plenary activity – true or false?
Plants grow faster on warm sunny days
Light is required for photosynthesis
Oxygen is required for photosynthesis
Photosynthesis speeds up in the cold
Plants produce glucose by photosynthesis
Glucose is converted to starch for storage
The equations for respiration and photosynthesis are identical
Plants only carry out respiration in the dark
Plants carry out respiration for 24 hours a day
Plants can use the carbon dioxide from respiration for photosynthesis
Plants can use the oxygen from respiration for photosynthesis
The limiting factors of photosynthesis include light, temperature and nitrogen levels
T
T
F
F
T
T
F
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T
T
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