Photosynthesis Environmental Factors 3

Question 1

Which of the following best describes how C4 plants adapt to hot, sunny environments compared to C3 plants?

Accepted Answer

C4 plants concentrate CO₂ around RuBisCO, reducing photorespiration

Answer

C4 plants pre-fix CO₂ in mesophyll cells and shuttle it to bundle sheath cells where RuBisCO operates in a high-CO₂ environment, suppressing the wasteful photorespiration pathway.

Question 2

A farmer notices that crop yield drops significantly when nighttime temperatures remain unusually high. Which physiological process best explains this?

Accepted Answer

Accelerated respiration consuming carbon fixed during the day

Answer

High nighttime temperatures increase dark respiration, causing plants to consume more of the sugars produced by daytime photosynthesis.

Question 3

What happens to the quantum yield of photosynthesis (moles of CO₂ fixed per mole of photons absorbed) as temperature increases above the optimum?

Accepted Answer

It decreases because photorespiration and protein denaturation accelerate

Answer

Above the temperature optimum, photorespiration rises and enzymes begin to denature, reducing the efficiency of carbon fixation per photon absorbed.

Question 4

Which gas, when elevated in the atmosphere, directly supplies the substrate for carbon fixation in photosynthesis?

Accepted Answer

Carbon dioxide (CO₂)

Answer

CO₂ is the inorganic carbon substrate that RuBisCO fixes into organic molecules during the Calvin cycle.

Question 5

Under which condition would a C3 plant most likely suffer the greatest reduction in net photosynthesis due to photorespiration?

Accepted Answer

Hot temperatures and low CO₂

Answer

Photorespiration is favored by high temperature (which increases O₂ solubility relative to CO₂) and low CO₂ (which shifts RuBisCO toward oxygenase activity).

Photosynthesis Practice Test

Photosynthesis Practice Test

Photosynthesis Environmental Factors 3