AP BIOLOGY

Detailed explanation-1: -These plants are called C4 plants, because the first product of carbon fixation is a 4-carbon compound (instead of a 3-carbon compound as in C3 or “normal” plants). C4 plants use this 4-carbon compound to effectively “concentrate” CO2 around rubisco, so that rubisco is less likely re react with O2.

Detailed explanation-2: -In the C4 pathway, initial carbon fixation takes place in mesophyll cells and the Calvin cycle takes place in bundle-sheath cells. PEP carboxylase attaches an incoming carbon dioxide molecul to the three-carbon molecule PEP, producing oxaloacetate (a four-carbon molecule).

Detailed explanation-3: -Under high temperature, high light, and the current CO2 concentration in the atmosphere, the C4 pathway is more efficient than C3 photosynthesis because it increases the CO2 concentration around the major CO2 fixating enzyme Rubisco.

Detailed explanation-4: -In the C3 plants, CO2 is assimilated by condensing with RuBP by the help of RuBisCO enzyme to yield the first stable product, three carbon compund PGA. In C4 plants, CO2 is assimilated by condensing with PEP, by the help of PEPCase enzyme to yield the first stable product, four carbon compound OAA.

Detailed explanation-5: -The response of C3 species to increased [CO2] may be more positive than that of C4 species because photosynthetic rate of C3 species increases by approximately 58% due to doubled [CO2] (Drake et al. 1997). However, in C4 species, the photosynthesis is nearly saturated under recent ambient [CO2] (von Caemmerer et al.