How do c4 plants differ from c3 plants?

How do C3 vs. C4 plants differ in photosynthesis response to light intensity?

• Answer:

  With increased light intensity comes increased air temperatures. Dark respiration is much more sensitive to temperature increases than photosynthesis rates. Leaf photorespiration increases sharply above 30 C because dissolved CO2 concentration decreases. This is why C4 plants dominate in the warmer climates, they minimize photorespiration by concentrating CO2 inside so RuBisCo reacts with CO2 not O2. C4 & CAM plants speed up the diffusion rate of CO2 by driving it into storage, at a slight cost. These plants have an additional step using PEPCase to catalyze: 3 carbon phosphoenolpyruvate (PEP) + CO2 => four carbon oxaloacatate (OAA) The ratio of carbon intake to energy molecules used C3 => 1 CO2 intake : (3 ATP + 2 NADPH) used C4 => 1 CO2 intake : (5 ATP + 2 NADPH) used C4 optimal operating temperature range is at 30C C3 optimal range is at 20C C3 photosynthesis rate of carbon fixation is lower than C4 so C3 Productivity is ~20 tons/ha/yr while C4 is ~30 tons/ha/yr C3 uses as much as 75% more water in transpiration than C4 to fix the same amount of carbon C3 primary CO2 acceptor RuBisCo and no secondary acceptor C4 primary CO2 acceptor PEPCase and RuBisCO as secondary CO2 acceptor C3 has one type of chloroplast C4 has 2 types (dimorphic)