The main energy source needed to perform cellular processes in single-celled organisms is typically a) ATP (Adenosine triphosphate). ATP serves as the primary energy currency of the cell, providing the energy required for various cellular activities.
- b) Photosynthesis refers to the process by which certain organisms convert light energy into chemical energy, but it is not the energy source itself.
- c) DNA is involved in genetic information and replication but does not serve as an energy source.
- d) Enzymes are catalysts that speed up biochemical reactions but do not provide energy by themselves.
Therefore, the correct answer is a) ATP.