Some cells contain large numbers of mitochondria while others have relatively few or none. this suggests that

Mitochondria is a double membrane organelle which is involved in the production of energy molecules of the cell called adenosine triphosphate or ATP.

The number of mitochondria in a cell is dependent on the function of the cell it is specialized to perform. For example:

1. The number of mitochondria in a muscle cell is very high as it requires a high amount of ATP molecules for contraction.

2. Mature red blood cells lack nucleus as they are specialized to perform carry oxygen molecules and do not require the ATP.

Thus, the number of mitochondria depends on the function of the cell.