What's the big difference between C3, C4, and CAM plants?

Answer 1

C3 carbon fixation is a metabolic pathway for carbon fixation in photosynthesis. This process converts co2 and ribulose bisphosphate into 3-phosphoglycerate through the following reaction:

6 CO2 + 6 RuBP → 12 3-phosphoglycerate

In C4 , carbon dioxide is drawn out of malate and into this reaction rather than directly from the air.
Since every CO2 molecule has to be fixed twice, the C4 pathway is more energy-consuming than the C3 pathway. The C3 pathway requires 18 ATP for the synthesis of one molecule of glucose while the C4 pathway requires 30 ATP. But since otherwise tropical plants lose more than half of photosynthetic carbon in photorespiration, the C4 pathway is an adaptive mechanism for minimizing the loss.

There are several variants of this pathway:
*The 4-carbon acid transported from mesophyll cells may be malate as above, or may be aspartate.
*The 3-carbon acid transported back from bundle-sheath cells may be pyruvate as above, or alanine.
*The enzyme which catalyses decarboxylation in bundle-sheath cells differs. In maize and sugarcane, the enzyme is NADP-malic enzyme, in millet, it is NAD-malic enzyme, and in Panicum maximum it is PEP carboxykinase.

Answer 2

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All plants use C3 as the basis but C4 plants have an additional step that separates the C3 & C4 cycles in space. The physical separation cost a bit more in energy but conserves water very well so works better in warmer climates with intense sunlight. The plants can take in CO2 needed for photosynthesis and still regulate the rate of water lost through transpiration. The additional C4 step holds CO2. CAM plants are C4 so hold the CO2 taken in while the stomata are open. The difference is that the stomata are open at night to have a controlled release of water vapor to drive the upward pull of water and dissolved nutrients in transpiration. Plants have to compromise between water loss and freely exchanging gases because they do not have separate pathways for water movement and gas exchange with the atmosphere. Both water and CO2 are rate limiting factors for photosynthesis to proceed but to get CO2 too much water can be lost and the plant injured by desiccation. The plant must shut off the stomata but then it cannot photosynthesize. By adding the separating step C4 plants pull the CO2 in and move in quickly away so the CO2 is always flowing in. This is what requires the extra energy, moving the CO2 faster so more can diffuse down the gradient the plant creates. The CO2 cannot be lost once internalized so this allows CAM plants to separate it in time as well as space. Some plants switch from C3 to CAM depending on habitat factors. CAM Bromeliads are epiphytes where water can be erratically available in the tree canopy despite living in a rainforest. After a rainy period the plant has water and opperated with the energy efficient C3. When they run out of water they switch to CAM and open the stomata at night to sequester the CO2 with less water lost then wait until daylight and the plant can photosynthesize again.

Answer 3

they differ in how they fix carbon. c3 appears to be the ancestral method.

"Thus, C4 metabolism physically separates CO2 fixation from the Calvin cycle, while CAM metabolism temporally separates CO2 fixation from the Calvin cycle."

Answer 4

c4 plants explode while the others implode :S