AP BIOLOGY

Detailed explanation-1: -ATP and NADPH use their stored energy to convert the three-carbon compound, 3-PGA, into another three-carbon compound called G3P. This type of reaction is called a reduction reaction, because it involves the gain of electrons. A reduction is the gain of an electron by an atom or molecule.

Detailed explanation-2: -ATP helps fuel the Calvin cycle in that it’s third phosphate can be removed-forming ADP-in order to provide energy for the cycle to occur. On the other hand, NADPH acts as a reducing agent, by converting into NADH so that high-energy electrons can be added to form saccharides.

Detailed explanation-3: -The ATP and NADPH from the light-dependent reactions are used to make sugars in the next stage of photosynthesis, the Calvin cycle. In another form of the light reactions, called cyclic photophosphorylation, electrons follow a different, circular path and only ATP (no NADPH) is produced.

Detailed explanation-4: -The overall purpose of the light-dependent reactions is to convert solar energy into chemical energy in the form of NADPH and ATP. This chemical energy will be used by the Calvin cycle to fuel the assembly of sugar molecules.

Detailed explanation-5: -Photosynthesis takes place in two distinct stages. In the light reactions, energy from sunlight drives the synthesis of ATP and NADPH, coupled to the formation of O2 from H2O. In the dark reactions, so named because they do not require sunlight, the ATP and NADPH produced by the light reactions drive glucose synthesis.