Question

1. the figure to the right illustrates an adaptation seen in c4 plants. describe what is happening in the figure.
2. why is this process demonstrated in the figure to the right beneficial to plants that live in hot, dry climates?

Explanation:

For question 3:
In C4 plants, carbon dioxide (\(CO_2\)) is first fixed in mesophyll cells. The enzyme in mesophyll cells combines \(CO_2\) with a 3 - carbon compound to form a 4 - carbon organic acid. This organic acid is then transported to bundle sheath cells. In bundle sheath cells, the 4 - carbon organic acid releases \(CO_2\), which then enters the Calvin cycle.
For question 4:
In hot, dry climates, plants tend to close their stomata to reduce water loss. When stomata are closed, the internal \(CO_2\) concentration drops. C4 plants' mechanism ensures that even when stomata are partially closed (to conserve water), the bundle sheath cells still get a relatively high - concentration of \(CO_2\). This is because the C4 pathway acts as a \(CO_2\) pump. The enzyme in mesophyll cells (PEP carboxylase) has a high affinity for \(CO_2\) even at low concentrations. By concentrating \(CO_2\) in bundle sheath cells, it reduces photorespiration (a wasteful process that occurs in C3 plants when \(CO_2\) is low and \(O_2\) is relatively high). So, C4 plants can more efficiently use the limited \(CO_2\) available when stomata are closed (to save water), and thus carry out photosynthesis more effectively in hot, dry conditions.

Answer:

1. In mesophyll cells, \(CO_2\) combines with a 3 - carbon compound to form a 4 - carbon organic acid. This acid is transported to bundle sheath cells, where it releases \(CO_2\) for the Calvin cycle.
2. In hot, dry climates, stomata close to reduce water loss. The C4 process acts as a \(CO_2\) pump. PEP carboxylase in mesophyll cells has a high affinity for \(CO_2\) (even at low levels). The transported 4 - carbon acid releases \(CO_2\) in bundle sheath cells, increasing the \(CO_2\) concentration there. This reduces photorespiration (a problem in C3 plants under low \(CO_2\) conditions when stomata are closed) and allows efficient photosynthesis with limited \(CO_2\) (while conserving water).