Most cells, with only very few exceptions, require nucleic acids of some sort to function. The most common is DNA (deoxyribonucleic acid), but some types of bacteria have only RNA (ribonucleic acid). In either case, nucleic acids contain the instructions for production of the proteins a cell needs to survive, and damage to a cell's nucleic acids can be deadly. Having the right DNA or RNA can also help a cell to function in less hospitable environments.
All cells need some sort of energy to survive. Animal cells and most types of bacterial cannot produce their own energy, and must consume other living or formerly living cells, either directly or indirectly. Plant cells do produce their own energy from water, air, and sunlight via photosynthesis. In any case, cells cease to function without energy. Most cells die quickly when deprived of energy, although many are able to store excess energy for future use.
Temperature has a profound impact on the speed of chemical reactions, and at any time, there are hundreds to thousands of chemical reactions going on in any given cell. Typically, warmer temperatures lead to increased speed of chemical reactions and higher metabolic needs, while cooler temperatures have the opposite effect. In addition, temperature extremes can damage components of a cell. For example, enzymes and other proteins may be denatured and even destroyed in excessively warm conditions.
Similar to temperature, pH can be a determining factor in whether or not a necessary chemical reaction in a cell occurs at the speed required for the cell's functioning, and the wrong pH can cause irreversible damage to cellular components. Thus, a too high or too low pH can have fatal consequences for a cell. Most living cells require a fairly neutral pH just above 7, though some bacteria thrive at higher and lower pH.
The cells in multi-cellular organisms may be strongly affected by signaling molecules produced by other cells within the same organism. These signaling molecules reach receptors on the cell membrane and trigger a cascade of intracellular reactions that profoundly affect the cell's functioning, both positively and negatively. In some cases, cells even rely on a continuous so-called survival signal produced by other cells to sustain life and will die in the absence of this survival signal.