Light

 

Is the ultimate source of energy.

The sun gives light to the plants, that give energy to the bacteria and fungi. The fungi are eaten by animals, and the animals get the energy form he fungi. When the animals die, the plants use their decomposed bodies for nourishment. None of this is able to happen, though, with our the sun.

With out photosynthesis the Earth's oxygen would not be replenished. With out oxygen the animals would not be able to survive. Respiration is equally as important as photosynthesis. With out respiration the plants would not be able to create ATP.

All three processes (photosynthesis, respiration, and decomposition) use energy.

Photosynthesis:
-Uses energy from the sun to create glucose.

Respiration:
-Glucose

Decomposition:
-Energy is taken from dead things