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Biochemistry

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Photosynthesis and ${ CO }_{ 2 }$ Compensation Points

BIOCHM-O4KSRG

Shown below is a graph of photosynthesis (Net ${ CO }_{ 2 }$ fixation) vs. atmospheric ${ CO }_{ 2 }$ concentration for a ${ C }_{ 3 }$ and a ${ C }_{ 4 }$ plant. For reference, the atmospheric [${ CO }_{ 2 }$] in the USA in 2016 is about 400 ppm.

Use your understanding of ${ C }_{ 3 }$ and ${ C }_{ 4 }$ photosynthesis and this diagram to select ALL of the following statements that are completely TRUE.

M. Rumpho-Kennedy. Created for Albert.io. Copyright 2016. All rights reserved.

A

Trace A represents a ${ C }_{ 4 }$ plant and the approximate ${ CO }_{ 2 }$ compensation point is 300 ppm.

B

Trace B represents a ${ C }_{ 3 }$ plant and the approximate ${ CO }_{ 2 }$ compensation point is 60 ppm.

C

The higher ${ CO }_{ 2 }$ compensation point observed for the ${ C }_{ 3 }$ plant is largely due to the higher affinity for internal ${ CO }_{ 2 }$ in ${ C }_{ 3 }$ compared to ${ C }_{ 4 }$ plants.

D

The lower ${ CO }_{ 2 }$ compensation point observed for the ${ C }_{ 4 }$ plant is largely due to the ability of ${ C }_{ 4 }$ plants to concentrate ${ CO }_{ 2 }$ internally.

E

If a ${ C }_{ 3 }$ and a ${ C }_{ 4 }$ plant were sealed in an illuminated chamber initially containing 400 ppm ${ CO }_{ 2 }$, the ${ C }_{ 3 }$ plant would likely out-live the ${ C }_{ 4 }$ plant.

F

An increase in atmospheric ${ CO }_{ 2 }$ concentration will likely benefit net photosynthesis in a ${ C }_{ 3 }$ plant more than a ${ C }_{ 4 }$ plant.