In photosynthesis, light is absorbed in order to move electrons from water molecules to NADPH.  The reduction of  to NADPH is accompanied by the movement of protons across a membrane which sets up a gradient similar to that of oxidative phosphorylation.  The protons eventually run through ATP synthase and ATP is formed.

During photosynthesis, the light phase is responsible for creating  which the dark phase then consumes as a part of its process. In addition to  is used in the dark phase as a high energy substrate to work properly.

Absorbing four photons by photosystem II creates one oxygen molecule, so absorbing 12 would produce 3 molecules of .

During photosynthesis, the dark phase follows the light phase. The light phase produces  which, along with , is fed into the dark phase where it is consumed (becomes  and ). If the light phase continues working, but the dark phase does not, the  and  created during the light phase will not be consumed. Thus, there will be a decrease in the level of  and  (the correct answer). The relative proportion of  will actually increase.

Carbohydrate production is a result of the dark phase working properly, so their levels would decrease in this instance. The sensitivity of the chloroplast to light would not change.

All of the answer choices are steps in the Calvin cycle, but the only one that describes the first stage - fixation - is  and ribulose 1,5-bisphosphate reacting to form 3-phosphoglycerate.

The stages of the Calvin cycle in the order that they occur are fixation, reduction, and then regeneration.  While carboxylation does occur as a part of the first stage, it is not what defines that stage.

Despite the Calvin cycle's other name (light independent reactions), light is indirectly required for this process to function. All other choices are true of the Calvin cycle.

The first step in glycolysis is the conversion of glucose to glucose-6-phosphate through the consumption on one ATP molecule. Glucose is reacted upon by the enzyme hexokinase to carry out this step. Kinases are a group of enzymes that add phosphate groups by removing them from an ATP. All of these other enzymes catalyze subsequent reactions in glycolysis.

Dihydroxyacetone phosphate (DHAP) is converted to glyceradehyde-3-phosphate (G3P) by the enzyme triose phosphate isomerase. As the name suggests, this enzyme catalyzes the isomerization of a three-carbon sugar into another three-carbon sugar. Since the molecular formulas of DHAP and G3P are the same, we know that they are isomers of each other.

The balance between DHAP and G3P is extremely important in regulating overall cell metabolism. DHAP is a precursor to triglycerides, and is used in their synthesis, while G3P is an intermediate in glycolysis, an ATP-producing process. In order to favor the conversion of DHAP into G3P, and not the opposite, the cell must keep G3P levels low (Le Chatelier's Principle). Consider the following equilibrium: . This should make sense: if there is lots of ATP around in the cell, there is no need for glycolysis to proceed. Thus the equilibrium will be pushed to the left, increasing the concentration of DHAP in the cell. In humans, DHAP is converted into triglycerides, which get stored as fat. One way to shift this equilibrium to the right is to "create" an ATP need. This can be done by exercising. Exercise utilizes ATP and will thus pull the equilibrium to the right, removing DHAP (which was destined to be converted into fat) and facilitates its conversion into G3P to proceed with cellular respiration. 

The tenth and final reaction of glycolysis involves the conversion of phosphoenolpyruvate (PEP) into pyruvate. This step is catalyzed by the enzyme pyruvate kinase. This kinase is going to remove a phosphate group from PEP and put it on ADP to yield ATP. Pyruvate, a three-carbon molecule, is the end product of glycolysis. It can be sent to the pyruvate dehydrogenase complex to be turned into acetyl-CoA, which enters the Krebs cycle. Alternatively, it can be reduced into lactate and/or ethanol (depending on the organism) to regenerate  for glycolysis via anaerobic respiration.