Photosynthetic organisms obtain their energy from sunlight, whereas chemosynthetic organisms get energy from inorganic chemical bonds. In fact they oxidize surfur compounds to obtain energy for chemosynthesis. CAM plants close their stomates during the daytime, when transpiration is potentially greater. They open them at night, when the air is cooler and the relative humidity is higher. In addition, the CAM photosynthetic mechanism is more efficient than C3 photosynthesis, in terms of water lost per carbon fixed.
Water has a number of unusual physical properties that are critical to life on earth.
Because ice is less dense than water, the bottoms of deep lakes and oceans seldom freeze, and so provide a refuge for aquatic plants and animals during winter. Water has low thermal conductivity and low latent heat, which allows poikilothermic organisms to quickly match body temperature to the changing temperature of their surroundings. Water is known as the universal solvent because it has a great capacity to dissolve inorganic compounds, making them accessible for living systems. Partial credit was given if the order of the quantities was partially correct, or was scored in reverse. More points were deducted if a quantity was 2 or 3 places out of rank than if only one place out of rank.