Temperature-sensitive mutations are useful in understanding essential life processes. A temperature-sensitive mutant will be normal at a lower (non-restrictive) temperature; when shifted to a higher (restrictive) temperature, the mutant will reveal its mutant (and potentially deleterious) phenotype. You isolate a plant with a temperature-sensitive mutation in the water-splitting complex. You grow the plant at a non-restrictive temperature, then shift it to its restrictive temperature. The outcome you would most expect to see upon shifting temperature would be

decreased NADPH production.
increased NADPH production.
no change in NADPH production.
decreased sugar production.
no change in sugar production.
increased oxygen production.

decreased NADPH production.

decreased sugar production.

Explanation:

The water-splitting complex is associated with PSII and serves as a donor of electrons to the reaction center of PSII. PSII loses its electrons upon trapping of sunlight. These electrons are passed finally to NADP reductase via electron transport chain and PSI. NADP reductase reduces NADP into NADPH. The NADPH formed during the light-dependent phase serves as reducing power in reactions of the Calvin cycle.  

A mutation in the water-splitting complex would result in no electron supply to PSII and thereby, reduced production of NADPH. The reduced NADPH production would limit the supply of reducing power for the Calvin cycle and the sugar production would be decreased.

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.