Factors affecting photosynthesis — practice questions

Question 1 · difficulty L1 · recall

According to Blackman law of limiting factors, what determines the rate of a process when several factors can affect it?

• A. The factor present in the greatest amount
• B. The factor closest to its limiting minimum
• C. The average value of all factors
• D. Only temperature

Question 2 · difficulty L2 · understanding

How does water shortage commonly reduce photosynthesis before severe dehydration damages the photosynthetic machinery?

• A. It converts C3 plants into C4 plants
• B. It immediately destroys all chlorophyll
• C. It raises internal carbon dioxide sharply
• D. Stomatal closure limits CO2 entry

Question 3 · difficulty L3 · application

Why may increasing light intensity fail to raise the photosynthetic rate of a well-lit leaf?

• A. Chlorophyll stops absorbing light above low intensity
• B. Light never affects photosynthesis
• C. Another factor, such as CO2, is limiting
• D. The Calvin cycle occurs only in darkness

Question 4 · difficulty L3 · application

A plant is supplied with abundant light and suitable temperature, but its photosynthetic rate rises when carbon dioxide concentration is increased. What was most likely limiting initially?

• A. CO2 availability
• B. Light intensity
• C. Temperature
• D. Chlorophyll presence

Question 5 · difficulty L4 · analysis

At the same high light intensity, a C4 plant maintains a higher photosynthetic rate than a C3 plant under warm conditions and relatively low internal carbon dioxide. What best explains the difference?

• A. C4 plants bypass the Calvin cycle entirely in bundle-sheath cells
• B. C4 CO2 concentration suppresses photorespiration
• C. C3 plants lack chlorophyll a
• D. C4 plants obtain ATP without light

Question 6 · difficulty L5 · analysis

A leaf is first kept at low light with abundant carbon dioxide, then moved to high light without changing carbon dioxide. Its photosynthetic rate rises initially and then plateaus. Adding more carbon dioxide causes another increase. Which sequence of limiting factors best explains the observations?

• A. Temperature was the only limiting factor throughout
• B. Carbon dioxide was limiting first, then light became limiting
• C. Light first, then CO2
• D. Water was necessarily limiting at both stages