The ultimate source of energy for the majority of organisms on Earth, including humans, is

A) heat from burning fuels.
B) heat from muscle contraction.
C) sunlight.
D) electric light.
E) ultraviolet light.

The ultimate source of energy for the majority of organisms on Earth is sunlight, which fuels photosynthesis. This process converts solar energy into chemical energy stored in the bonds of organic molecules such as glucose. This energy can then be harnessed by organisms through cellular respiration to power their metabolism and life processes. While heat from burning fuels and muscle contraction can also provide energy for some organisms, they ultimately trace back to sunlight as the original source of energy. Electric and ultraviolet light are not significant sources of energy for organisms on Earth.