Photosynthesis- Limiting Factors (4.3.1)

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What is a limiting factor?
The factor which is present in the lowest or least favourable value, it is limiting the rate of reaction.
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What can limiting factors of photosynthesis be?
Light intensity, carbon dioxide concentration and temperature.
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What are the three ways that light intensity can affect the rate of PHS?
Causes stomata to open, increasing the availability of CO2. Excites electrons from the chlorophyll molecules in the light-dependent stage. Provides the energy needed for photolysis, providing hydrogen ions.
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Give 2 ways that carbon dioxide is added to the atmosphere.
Burning fossil fuels. Respiration of all living organisms.
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How do plants absorb carbon dioxide?
Diffusion through the stomata.
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How is a carbon dioxide diffusion gradient created in a leaf?
During daylight, carbon dioxide is used in the Calvin cycle in the chloroplasts, so the conc. is lower in the leaf than in the air.
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How does temperature affect the light-dependent stage?
The rate of the light-dependent reactions isn't directly affected by temperature, because the energy that drives them comes from light, not the k.e of molecules.
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Why do plant enzymes often have lower optimum temperatures?
They have evolved to work in the environmental temperatures in which the plant normally lives.
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Why does a high temperature limit the rate of photosynthesis?
There is more transpiration via the stomata, and so the plant closes the stomata to save water. This limits the availability of carbon dioxide.
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What is photorespiration?
The enzyme rubisco switches from catalysing a reaction between CO2 and RuBP to catalysing a reaction between O2 and RuBP. This wastes the RuBP.
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When does photorespiration occur?
During an increase in temperature.
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How does light affect the light-independent stage of photosynthesis?
Without light, the Calvin cycle will stop because the light-dependent stage stops and so there is no supply of ATP and NADP to the Calvin cycle. The GP can't be converted to TP, so it builds up.
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How does CO2 conc. affect the light-independent stage of PHS?
If CO2 is in short supply, less GP is made and so less TP is made. The lack of CO2 means there's less for the RuBP to react with so RuBP may build up.
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Card 2

Front

What can limiting factors of photosynthesis be?

Back

Light intensity, carbon dioxide concentration and temperature.

Card 3

Front

What are the three ways that light intensity can affect the rate of PHS?

Back

Preview of the front of card 3

Card 4

Front

Give 2 ways that carbon dioxide is added to the atmosphere.

Back

Preview of the front of card 4

Card 5

Front

How do plants absorb carbon dioxide?

Back

Preview of the front of card 5
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