All of the following need to be present for a plant to do photosynthesis except

light

water

oxygen

carbon dioxide

Oxygen is a by-product of photosynthesis thus it is not needed for photosynthesis to occur.  

Light is needed to provide the energy needed as photosynthesis is endothermic and is also needed to ionise the water molecule to get hydroxide and hydrogen ions and carbon dioxide is what is reduced to starch.

C: plants and animals

Firstly, the water in the dams hold gravitational potential energy as they are above ground level. the gravitational potential energy is then transferred to kinetic energy as it falls, spinning the turbinethe turbine then spins the generator, which is a large magnet surrounded by metal coils. by doing this, the generator generates electricity. in this action, the energy transfer taken place is kinetic to electric energy