BioInteractive Regulation and Efficiency of Photosynthesis 1 — Questions and Answers
Question 1: What is the light compensation point in photosynthesis?
- The light intensity at which photosynthesis exactly equals cellular respiration (Correct answer)
- The point at which a plant needs the most water
- The maximum light a plant can absorb
- The intensity at which chlorophyll is produced
Correct answer: The light intensity at which photosynthesis exactly equals cellular respiration
At the light compensation point, the rate of CO2 fixed by photosynthesis equals the rate of CO2 released by cellular respiration, resulting in no net gas exchange.
Question 2: How does temperature affect the rate of photosynthesis?
- It affects enzyme activity; rates increase with temperature up to an optimum, then fall sharply (Correct answer)
- Temperature has no effect on photosynthesis
- Higher temperatures always increase photosynthesis
- Low temperatures increase photosynthesis indefinitely
Correct answer: It affects enzyme activity; rates increase with temperature up to an optimum, then fall sharply
Photosynthesis increases with temperature up to the enzyme's optimal temperature, above which enzymes denature and the rate falls rapidly.
Question 3: Which environmental factor is a limiting factor for photosynthesis at low concentrations despite abundant light?
- Carbon dioxide (Correct answer)
- Oxygen
- Nitrogen
- Potassium
Correct answer: Carbon dioxide
When CO2 levels are low, they limit the rate of the Calvin cycle even if light and water are abundant, because RuBisCO cannot fix carbon faster than CO2 diffuses in.
Question 4: What is the concept of limiting factors in photosynthesis?
- The factor in shortest supply relative to the plant's needs that controls the overall rate of photosynthesis (Correct answer)
- The maximum CO2 a leaf can absorb
- The enzyme that limits electron transport
- The minimum ATP needed for carbon fixation
Correct answer: The factor in shortest supply relative to the plant's needs that controls the overall rate of photosynthesis
Blackman's law of limiting factors states that the rate of photosynthesis is controlled by whichever factor — light, CO2, or temperature — is present at the least favorable level.
Question 5: How do stomata regulate photosynthesis?
- By controlling CO2 entry and water vapor exit, balancing gas exchange with water conservation (Correct answer)
- By absorbing light energy
- By producing chlorophyll on demand
- By storing glucose produced in the Calvin cycle
Correct answer: By controlling CO2 entry and water vapor exit, balancing gas exchange with water conservation
Stomata open to allow CO2 in for photosynthesis but simultaneously allow water to escape; plants regulate stomatal aperture to balance carbon gain against water loss.
Question 6: What triggers guard cells to open stomata during daylight?
- Light-driven K+ influx and the accumulation of osmolytes that increase guard cell turgor (Correct answer)
- Dark conditions causing K+ efflux
- High CO2 concentrations inside the leaf
- Drop in leaf temperature
Correct answer: Light-driven K+ influx and the accumulation of osmolytes that increase guard cell turgor
In daylight, guard cells use light energy to pump K+ and other ions inward, raising osmotic potential and turgor pressure, which swells the guard cells and opens the stoma.
BioInteractive Regulation and Efficiency of Photosynthesis 1
What is the light compensation point in photosynthesis?