Special Adaptations of C 4 and CAM Plants (Unit 7.12) James Michael Shefali
C 3 Plants CC 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. CC 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 TThe process C 3 plants must perform after the Calvin cycle when their stomata are closed. TThe 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. PPhotorespiration 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 CCAM stands for crassulacean acid metabolism. CCAM plants are also adapted to prevent wasteful photorespiration. CCAM 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