Photosynthesis Environmental Factors 2

Question 1

Which wavelengths of visible light are LEAST effective at driving photosynthesis?

Accepted Answer

Green wavelengths (~550 nm)

Answer

Chlorophyll reflects green light rather than absorbing it, making green wavelengths the least effective for photosynthesis.

Question 2

At what approximate CO₂ concentration does photosynthesis in C3 plants typically become CO₂-saturated under normal conditions?

Accepted Answer

1000 ppm

Answer

Most C3 plants reach CO₂ saturation around 1000 ppm; above this, additional CO₂ provides little additional benefit.

Question 3

How does drought stress reduce photosynthesis even when light and CO₂ are plentiful?

Accepted Answer

It causes stomata to close, limiting CO₂ entry

Answer

Under drought, plants close stomata to conserve water, which simultaneously restricts CO₂ diffusion into the leaf.

Question 4

Which environmental factor most directly determines the rate of the light-independent (Calvin cycle) reactions?

Accepted Answer

Temperature, by affecting enzyme activity

Answer

The Calvin cycle is enzyme-driven; temperature directly governs RuBisCO and other enzyme kinetics, making it the primary controlling factor.

Question 5

A plant is moved from a shaded forest floor to full sunlight. Which of the following responses is most likely in the short term?

Accepted Answer

Photoinhibition and possible bleaching of chlorophyll

Answer

Sudden excess light can overwhelm the photosynthetic apparatus, leading to photoinhibition and oxidative damage to chlorophyll.

Photosynthesis Practice Test