Question

In CAM metabolism Select one: a. fixed carbon is shuttled from mesophyll to bundle sheath cells b. the problems of photorespiration are reduced by isolating the enzyme PEP carboxylase from high levels of dissolved O2 c. carbon fixation by the Calvin cycle occurs at night to avoid photorespiration d. carbon is fixed via C4 metabolism at night and by the Calvin cycle in the day e. fixed carbon is stored in the vacuole in the form of G3P, a 4 carbon compound

Answer 1

d. carbon is fixed via C4 metabolism at night and by the Calvin cycle in the day

Step-by-step explanation:

CAM plants live in extremely dry and hot environments. These species have adapted to take CO₂ in arid and semiarid areas by opening stomas during the night, when the temperature decreases and humidity increases, to avoid excessive water loss and dehydration. During the day, the temperature increases, so these plants close stomas to avoid transpiration and not to lose water. Hence, CAM plants have almost no requirements for water during CO₂ fixation.

So the strategy of these plants is to separate temporarily two processes. Both of them occur in the mesophil of the leaves, but not simultaneously.

• During the night, it occurs the Hach and Slack cycle, taking CO₂ with open stomas. As it happens in C4 plants, PEP-carboxylase fixates CO₂ in oxaloacetate, which then turns into malic acid that is stored in vacuoles of the photosynthetic cells.

• And during the day, the Calvin cycle takes place, with closed stomas to avoid transpiration.

The malic acid is synthesized in big amounts during the night, and it decarboxylates during the day releasing CO₂ that will be used in the Calvin cycle to produce carbohydrates.