Increased temperature means greater average energy of motion, so most substances expand when heated. In solids, the atoms are closely locked in position and can only vibrate. In gases, the atoms or molecules have still more energy and are free of one another except during occasional collisions. The temperature and acidity of a solution influence reaction rates. Many substances dissolve in water, which may greatly facilitate reactions between them.
Every cell is covered by a membrane that controls what can enter and leave the cell.
In all but quite primitive cells, a complex network of proteins provides organization and shape and, for animal cells, movement.