3.4 Alternative Mechanisms of Carbon Fixation

a photosynthetic pathway of carbon fixation that reduces the amount of photorespiration that takes place by continually pumping CO2 molecules (via malate) from mesophyll cells into bundle-sheath cells, where rubisco brings them into the C3 Calvin cycle.

C4 photosynthesis

During the cool of evening, CAM plants open their stomata. What gas is preferentially absorbed at this time?

During the cool of evening, CAM plants open their stomata. The gas that is preferentially absorbed at this time is CO2.

How does temperature affect the relative amounts of photosynthesis and photorespiration that occur in C3 plants?

In tropical climates, the persistent warm temperatures exacerbate this problem in C3 plants. Since the optimum temperature for photorespiration is much higher than that for photosynthesis, photorespiration rates may still be increasing when that ofC3 photosynthesis is starting to decline. Hot, dry, bright days produce the conditions that facilitate photorespiration. Dependence of photosynthesis and photorespiration on temperature in C3 plants. When photosynthesis rates start to decrease, photorespiration rates continue to increase.

Define photorespiration.

Photorespiration is a process which includes the oxidation of RuBP by rubisco and oxygen in light to form glycolate, which subsequently releases carbon dioxide.

Compare the end products of photosynthesis and photorespiration.

Photosynthesis, in the presence of sunlight and Chlorophyll, resulting in the formation of water, oxygen and glucose as end products. The products of photorespiration is glycolate, which subsequently releases carbon dioxide.

Why do plants that use CAM photosynthetic pathways close their stomata during the day?

Plants use CAM photosynthetic pathways close their stomata during the day to reduce water loss.

What gas can compete with CO2 for the binding site of the enzyme rubisco?

The gas that can compete with CO2 for the binding site of the enzyme rubisco is oxygen.

What is the main difference between the ideal environments of C4 plants and CAM plants?

The main difference between the ideal environments of C4 plants and CAM plants is that C4 plants are in hot, dry environments, while CAM plants are in hot, dry, desert environments

Under normal conditions, what proportion of fixed carbon is affected by photorespiration in C3 plants?

The proportion of fixed carbon that is affected by photorespiration in C3 plants is 20%.

What type of cell-cell connection do malate and pyruvate go through to move from one cell into the other?

The type of cell-cell connection do malate and pyruvate go through to move from one cell into the other is plasmodesmata.

Explain how this gas is stored for daytime use.

This gas is stored for daytime use since the stomata open at night, so that plants can take in CO2 and incorporate it into organic acids and close during the day to allow the organic acids to release CO2 molecules that enter the C3 Calvin cycle to be fixed into carbohydrates.

Name two C4 plants and two CAM plants.

Two C4 plants (hot, dry environments) are sugar cane and corn. Two CAM plants (hot, dry, desert environments) are cacti and pineapples.

At what time of the day would you expect to find the most malate in CAM plants?

You would expect to find the most malate in CAM plants late at night.

When would you find the least amount of malate in CAM plants?

You would find the least amount of malate in CAM plants at the evening.

a photosynthetic mechanism in which stomata open at night so that plants can take in CO2 and incorporate it into organic acids, and close during the day to allow the organic acids to release CO2 molecules that enter the C3 Calvin cycle to be fixed into carbohydrates

crassulacean acid metabolism (CAM)

oxidation of RuBP by rubisco and oxygen in light to form glycolate, which subsequently releases carbon dioxide

photorespiration

membrane-lined channels between plant cells that allow for the movement of some substances from cell to cell

plasmodesmata