17.4 Factors Affecting Photosynthesis

Question 1

What is a limiting factor?

Answer 1

the factor which is is shortest supply

limits the rate of reaction

Question 2

What are the possible limiting factors of photosynthesis?

Answer 2

• LIGHT INTENSITY
• CARBON DIOXIDE CONCENTRATION
• TEMPERATURE

Question 3

Why is water not considered a limiting factor of photosynthesis?

Answer 3

water potential must be extremely low to be considered a limiting factor

so low, that plant will have stopped photosynthesising

Question 4

Why is light intensity a limiting factor of photosynthesis?

Answer 4

light intensity controls rate of NADPH + ATP formation

in light-dependent stage

therefore limits rate of photosynthesis

Question 5

Why is carbon dioxide concentration a limiting factor of photosynthesis?

Answer 5

carbon dioxide controls rate of CO₂ fixation in calvin cycle + GP + TP formation

Question 6

Why is temperature a limiting factor of photosynthesis?

Answer 6

temperature influences kinetic energy of molecules

+ frequency of successful collisions

so controls rate of enzyme-controlled reactions

Question 7

Describe & explain the pattern shown by this graph:

Answer 7

1. increasing light intensity increases rate of photosynthesis, because light intensity is limiting.
2. After certain point, graph plateaus. Increasing light intensity does not increase rate, because other factors become limiting.

other factors are low: plateaus at lower light intensity & rate, because light intensity does not need to increase by a lot for other factors to become limiting.

other factors are high: plateaus at higher light intensity & rate, because light intensity needs to increase by a lot for other factors to become limiting.

Question 7

Describe & explain the pattern shown by this graph:

Answer 7

1. increasing light intensity increases rate of photosynthesis, because light intensity is limiting.
2. After certain point, graph plateaus. Increasing light intensity does not increase rate, because other factors become limiting.

other factors are low: plateaus at lower light intensity & rate, because light intensity does not need to increase by a lot for other factors to become limiting.

other factors are high: plateaus at higher light intensity & rate, because light intensity needs to increase by a lot for other factors to become limiting.

Question 8

What is the effect of decreasing light intensity on the calvin cycle?

Answer 8

• ￬ rate of light-dependent stage
  
  • reduced rate of NADPH + ATP formation
  • GP accumulates, since cannot be converted to TP using NADPH + ATP from light-dependent stage
  • decreased rate of RuBP formation, since used up to form GP but not regenerated.