Temperature, pressure and composition.
One reason is because the short days and long nights prevent the earth from warming up, another reason could be because the sun's rays in winter are more spread out thus minimizing the amount of energy
Substance abuse can spread STIs because when a user shares needles with an infected person, it can spread through the blood. Any high-risk behavior like this spreads STIs.
Water is used in many reactions in the body, both enzymatic and chemical. Water within blood and lymphatic system is responsible for the transport of hormones, antidotes oxygen and nutrients.
Metabolism can be described as entirety of chemical reactions which take place within a cell, the result of which is energy for processes which take place in the body.
