Photosynthesis Environmental Factors 5

Question 1

What is the concept of 'sun acclimation' in leaves, and how does it relate to environmental factors?

Accepted Answer

Sun leaves develop higher photosynthetic enzyme density and smaller cells to handle high irradiance

Answer

Leaves grown in high light (sun leaves) acclimate by increasing RuBisCO and chlorophyll density per cell and developing thicker mesophyll, maximizing carbon gain at high irradiance.

Question 2

In a FACE (Free-Air CO₂ Enrichment) experiment, which type of plant consistently shows the largest relative increase in photosynthesis when CO₂ is doubled?

Accepted Answer

C3 plants because they are furthest from CO₂ saturation at ambient levels

Answer

C3 plants operate below their CO₂ saturation point at ambient CO₂ levels, so doubling CO₂ provides the greatest stimulation of RuBisCO activity.

Question 3

Which environmental factor primarily controls the opening and closing of stomata on a minute-to-minute basis during the day?

Accepted Answer

Light intensity and CO₂ concentration sensed by guard cells

Answer

Guard cells respond directly to light (via phototropin and chloroplast signals) and internal CO₂ levels, adjusting stomatal aperture to balance gas exchange and water loss.

Question 4

A scientist finds that spraying plants with abscisic acid (ABA) reduces their photosynthesis rate on a sunny day. What is the most direct mechanism?

Accepted Answer

ABA triggers stomatal closure, reducing CO₂ availability in the leaf

Answer

ABA is the primary drought stress hormone that signals guard cells to close stomata, which limits CO₂ diffusion into the mesophyll and reduces the Calvin cycle rate.

Question 5

How does waterlogged (anaerobic) soil indirectly reduce leaf photosynthesis?

Accepted Answer

Root hypoxia impairs mineral and water uptake, triggering stomatal closure and ABA production

Answer

Anaerobic roots cannot maintain normal respiration, impairing ion and water transport; the resulting water and nutrient stress triggers ABA production and stomatal closure in leaves.

Photosynthesis Practice Test

Photosynthesis Practice Test

Photosynthesis Environmental Factors 5