Organisms at the bottom of the pyramid produce enough usable chemical energy to support the entire ecosystem through
a) predation.
b) photosynthesis.
c) cell respiration.
d) anaerobic respiration.

The correct answer is -

B) photosynthesis

Explanation:

Photosynthesis can be described as process of creating food (in the form of glucose) in green plants, algae, and some protist (that are called producers). It uses inorganic molecules that are carbon dioxide and water in the presence of energy from sunlight to synthesise glucose and release oxygen as waste in surroundings.

It takes place in the specialized membrane bound organelles, called chloroplast.

Producers occupy the base of any food chain, which can be represented by energy pyramid, thus they produce enough chemical energy to support the entire ecosystem through photosynthesis.

then that particular organisms become extinct.

i think it is true in my reasonment ..