C4 and CAM photosynthesis

Question 1

Role of RuBisCo

Answer 1

Binds CO2 and fixes carbon into the
organic 3-PGA, thus initiating the Calvin cycle.

Question 2

Photorespiration

Answer 2

A wasteful process in plants initiated by Rubisco that limits photosynthesis.

Question 3

Factors that influence Rubisco to bind to CO2 or O2

Answer 3

Substrate concentration - the more of a substrate the higher chance of binding to an enzyme. When the stomata close in hot/dry conditions to conserve water, oxygen cannot diffuse out, increasing its concentration when it’s produced in the light-dependent stage.
Temperature - at higher temps, Rubisco has a higher affinity for O2.

Question 4

C3 plants

Answer 4

Have no adaptations to prevent photorespiration, both stages occur in the mesophyll cell, named after the 3-carbon PGA the initial carbon fixation produces.

Question 5

C4 plants

Answer 5

Initial carbon fixation occurs in the mesophyll cell, and the rest of the Calvin Cycle occurs in the bundle-sheath cells. Named after the first four-carbon molecule produced in initial carbon fixation.

Question 6

Initial carbon fixation in C4 plants

Answer 6

CO2 enters mesophyll cells & is fixed by PEP carboxylase. Adding the carbon from CO2 to 3-carbon PEP to create a 4-carbon molecule. Then, oxaloacetate is converted to malate which can be transported to the bundle-sheath cells. After, malate breaks down into CO2 (for the Calvin Cycle) and PEP (to get transported back).

Question 7

How do C4 plants prevent photorespiration?

Answer 7

With the mesophyll cells constantly pumping a source of CO2 (malate) into the bundle-sheath cells, there is always a higher concentration of CO2 for Rubisco rather than O2.

Question 8

Cost of C4 photosynthesis

Answer 8

Namely, ATP is required to convert pyruvate to PEP for the initial carbon fixation. Because of this, C4 plants use more energy to undertake photosynthesis than C3 plants.

Question 9

CAM plants

Answer 9

At night, CAM plants open their stomata to bring in CO2, which is stored as malate in a vacuole. In the day, CAM plants don’t open their stomata (to decrease water loss), they use the stored malate which enters the bundle-sheath cells. After, malate breaks down into CO2 (for the Calvin Cycle) and PEP (to get transported back).

Question 10

Ideal temp for C3 plants

Answer 10

15-25°C

Question 11

Ideal temp for C4 plants

Answer 11

30-40°C (hot)

Question 12

Ideal temp for CAM plants

Answer 12

> 40°C (dry/arid)