What types of organisms will be affected by a decreased supply of water in an ecosystem? a. producers, consumers, and decomposers will be affected. b. producers and consumers will be affected. c. consumers and decomposers will be affected. d. no organisms will be affected.

B, for sure. Producers, Like grass and Flowers need water to make food. Consumers, like Cats, Snakes and Boars need water to drink so our internal systems will function properly. 
Im not sure if decomposers need water, but if there is less water then more animals die and they get food. so, not sure about that one.

Very minute and important evidence needs to be collected in order together detail and figure out what had happened

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.