Special Adaptations of C 4 and CAM Plants (Unit 7.12) James Michael Shefali

C 3 Plants CC 3 plants absorb the carbon dioxide they use in the Calvin Cycle directly from the atmosphere; this means that they must keep their stomata open most of the time despite the water loss this entails. CC 3 plants grow poorly in hot, dry climates as they cannot keep their stomata closed due to the need for a constant supply of CO 2.

 C 3 plants are very common and found in many parts of the world.  C 3 plants don’t grow very well in weather which is hot and dry.  Examples include soybeans, oats, wheat, and rice.

Photorespiration TThe process C 3 plants must perform after the Calvin cycle when their stomata are closed. TThe breakdown of the 2 carbon compound produced by the Calvin cycle when CO 2 levels fall low, producing H 2 O and CO 2. The two carbon compound is in turn produced when O 2 is added to the RuBP in the Calvin cycle instead of the CO 2 normally combined with RuBP. PPhotorespiration does not produce sugar or ATP and wastes carbon.

C 4 Plants  C 4 plants are adapted to prevent wasteful cellular respiration.  C 4 plants contain an enzyme which can continue to fix carbon when CO 2 levels are low. They produce a 4-carbon compound which shuttles all of the plant’s CO 2 into certain cells known as bundle-sheath cells. The CO 2 concentration in these cells remains high enough for the Calvin cycle to occur.

 C 4 plants are able to keep their stomata closed most of the time. As a result, they grow better in warmer, drier environments.  Examples include sugarcane, maize, and many grasses.

CAM Plants CCAM stands for crassulacean acid metabolism. CCAM plants are also adapted to prevent wasteful photorespiration. CCAM plants take in CO 2 only during the cool night. They then fix the CO 2 into a 4-carbon compound, the form in which CO 2 is stored until it is needed. During the day, this stored CO 2 is released into the Calvin cycle, keeping photosynthesis operating.

 CAM plants keep their stomata closed during the day, only opening them at night to take in CO 2. As a result, they are able to grow in very dry climates  Examples include pineapples, many cacti, ice plants, and jade plants.

4-C Mesophyll cell Bundle-sheath cell 3-C sugar Night Day C4 plant CAM plant

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