Explain why a cell with a large number of mitochondria is likely to be very active, and explain what a student would need to use to see a mitochondrion clearly.

Mitochondria are the sites of aerobic respiration, where glucose is oxidised to produce ATP. Aerobic respiration releases large amounts of energy that the cell can use for work. A cell containing many mitochondria can carry out more respiration simultaneously, producing more ATP and therefore being able to perform more metabolic activity.

A mitochondrion is too small to be resolved by a light microscope. To see it clearly, an electron microscope is required, as it provides the necessary resolution to visualise organelles of this size.