C4 plants?

Question

Why are C4 plants so efficient?

a) the enzyme they use to fix CO2 to RuBP is not attracted to O2.

b) they carry out the light reactions and the Calvin cycle in separate cells.

c) they have guard cells that keep oxygen molecules out of their leaves.

d) they have guard cells that keep carbon dioxide molecules out of their leaves.

Answer 1

because

Answer 2

You can find your answer here:

"The enzyme that catalyzes the joining of RuBP and CO2 is known as RuBP carboxylase, also called Rubisco. Rubisco is believed to be the most abundant protein in the world. However, Rubisco is not very efficient at grabbing CO2, and it has an even worse problem. When the concentration of CO2 in the air inside the leaf falls too low, Rubisco starts grabbing oxygen instead. The ultimate result of this process, called photorespiration, is that sugar is burned up instead of being created. Photorespiration becomes a significant problem for plants during hot, dry days, when they must keep their stomates (leaf pores) closed to prevent water loss.

Diverse groups of plants have evolved different systems for coping with the problem of photorespiration. These plants, called C4 plants and CAM plants, initially bind carbon dioxide using a much more efficient enzyme. This allows a more efficient harvest of CO2, allowing the plant to trap sufficient CO2 without opening its stomates too often. Each then uses the CO2 in the Calvin-Benson cycle.

C4 ("four-carbon") plants initially attach CO2 to PEP (phosphoenolpyruvate) to form the four-carbon compound OAA (oxaloacetate) using the enzyme PEP carboxylase. This takes place in the loosely packed cells called mesophyll cells. OAA is then pumped to another set of cells, the bundle sheath cells, which surround the leaf vein. There, it releases the CO2 for use by Rubisco. By concentrating CO2 in the bundle sheath cells, C4 plants promote the efficient operation of the Calvin-Benson cycle and minimize photorespiration."

From: http://www.biologyreference.com/Bl-Ce/C4...