Photosynthesis Determinants of Photosynthetic Rate 3

Question 1

Which mineral nutrient deficiency most directly reduces the rate of photosynthesis by limiting chlorophyll production?

Accepted Answer

Magnesium

Answer

Magnesium is the central atom in the chlorophyll molecule, so its deficiency leads to chlorosis and reduced photosynthetic capacity.

Question 2

In a compensation point experiment, net photosynthesis equals zero. What does this mean?

Accepted Answer

Gross photosynthesis exactly equals the rate of respiration

Answer

At the compensation point, carbon fixed by photosynthesis equals carbon released by respiration, so there is no net gas exchange.

Question 3

How does increasing nitrogen supply typically affect photosynthetic rate?

Accepted Answer

Increases it by enabling more RuBisCO and chlorophyll synthesis

Answer

Nitrogen is essential for synthesizing proteins such as RuBisCO and for the porphyrin ring of chlorophyll, so more nitrogen supports greater photosynthetic capacity.

Question 4

Why does photorespiration reduce net photosynthesis in C3 plants at high temperatures?

Accepted Answer

RuBisCO oxygenates O₂ instead of CO₂, releasing CO₂ without fixing carbon

Answer

At high temperatures, O₂ solubility increases relative to CO₂ and RuBisCO's oxygenase activity rises, consuming energy and releasing CO₂ through photorespiration.

Question 5

Which adaptation allows C4 plants to maintain higher photosynthetic rates in hot, dry conditions compared to C3 plants?

Accepted Answer

They concentrate CO₂ around RuBisCO in bundle sheath cells, suppressing photorespiration

Answer

C4 plants use PEP carboxylase in mesophyll cells to fix CO₂ into 4-carbon acids, then concentrate CO₂ in bundle sheath cells where RuBisCO operates, minimizing photorespiration.

Photosynthesis Practice Test

Photosynthesis Practice Test

Photosynthesis Determinants of Photosynthetic Rate 3