Special Adaptations of C4 and CAM

Plants (Unit 7.12)James

Michael Shefali

C3 Plants C3 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.

C3 plants grow poorly in hot, dry climates as they cannot keep their stomata closed due to the need for a constant supply of CO2.

C3 plants are very common and found in many parts of the world.

C3 plants don’t grow very well in weather which is hot and dry.

Examples include soybeans, oats, wheat, and rice.

Photorespiration

The process C3 plants must perform after the Calvin cycle when their stomata are closed.

The breakdown of the 2 carbon compound produced by the Calvin cycle when CO2 levels fall low, producing H2O and CO2. The two carbon compound is in turn produced when O2 is added to the RuBP in the Calvin cycle instead of the CO2 normally combined with RuBP.

Photorespiration does not produce sugar or ATP and wastes carbon.

C4 Plants C4 plants are adapted to prevent wasteful

cellular respiration. C4 plants contain an enzyme which can

continue to fix carbon when CO2 levels are low. They produce a 4-carbon compound which shuttles all of the plant’s CO2 into certain cells known as bundle-sheath cells. The CO2 concentration in these cells remains high enough for the Calvin cycle to occur.

C4 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 CAM stands for crassulacean acid metabolism. CAM plants are also adapted to prevent

wasteful photorespiration. CAM plants take in CO2 only during the cool

night. They then fix the CO2 into a 4-carbon compound, the form in which CO2 is stored until it is needed. During the day, this stored CO2 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 CO2. As a result, they are able to grow in very dry climates

Examples include pineapples, many cacti, ice plants, and jade plants.

4-C 4-C

Mesophyll cell

Bundle-sheath cell 3-C sugar 3-C sugar

Night

Day

C4 plant CAM plant

THE END