C4 and CAM Plants- Chapter 8

why are they called C3 plants

because in the Calvin Cycle, their first product is 2 PGA, which have three carbon each

C3 plants

regular plants

why are they called C4 plants

because the first product they make is a 4-carbon compound

photorespiration

light and respiration (doesn’t produce sugar or ATP)

occurs in all plants

Rubisco only fixes oxygen 20% of the time, initiating this process that recycles a toxic compound and costs the plant energy it could have used during photosynthesis

1. the stoma accidentally lets in O2 rather than CO2 for photosynthesis

2. rubisco adds whichever molecule is abundant and binds it to RuBp

*sometimes O2 may bond with H from NADPH to make water instead of going through photorespiration

Rubisco

an enzyme that fixes Co2 but can also fix O2 (can use either molecule as a substrate)

CAM and C4 plants

main goal is to limit the loss of water and control the rate of photosynthesis

C4 risks water loss and CAM risks respiration (they have to keep more water compared to C3 plants)

CAM plants

exs: pineapple, aloe vera, orchids, snake plants

CAM stand for Crassulacean Acid Metabolism and it allows plants to open its stomata at night more instead of the day (plants still open their stomata during the day but not as much)

• this helps to conserve water by reducing evapotranspiration

these plants perform double carbon dioxide fixation

• the Co2 acceptor in CAM plants is Phosphoenol pyruvic acid (PEP) during the night and is stored during the day

• PEP makes a 4 carbon compound, which turns tot malatate and is stored

• RuBP is the CO2 acceptor during the day and is stored at night in the vacuole

evapotranspiration

when a plant sweats and loses water (like dew) and the sun evaporates it

C4 plants

exs: sugarcane, corn

have unique leaf anatomy that allows CO2 to concentrate in “bundle sheath” cells around Rubisco enzyme

• sheath delivers CO2 straight to Rubisco, effectively removing its contact with oxygen and the need for photorespiration

  • this prevents water loss (allows plant to retain water through the ability to continue fixing carbon while stomata is closed)

1. CO2 changes to a 4 carbon compound (PEP bonds with CO2 to make oxaloacetic acid (OAA)

2. OAA changes to malatate

3. malatate releases CO2 for the Calvin cycle

Epiphytes

plants that grow on other plants and doesn’t hurt them

ex: vines, orchid, etc.

amneosperms

plants whose leaves fall off in the fall

gemnosperms

christmas trees

leaves do not fall off and they produce pinecones