In the human body, muscle cells have an increased need for energy during exercise.  To help supply this energy, the cells will contain more of which organelle?

The organelle that muscle cells will contain more of during exercise to help supply energy is the mitochondria. Here's why:

1. The mitochondria is often referred to as the "powerhouse of the cell". This is because it is responsible for producing adenosine triphosphate (ATP), the cell's main source of energy.

2. During exercise, muscle cells require more energy to contract and function effectively. This increased demand for energy means that more ATP needs to be produced.

3. To meet this increased demand for ATP, muscle cells will contain more mitochondria. The additional mitochondria allow for more ATP to be produced, thereby supplying the muscle cells with the energy they need during exercise.

4. Therefore, during periods of exercise, muscle cells will contain more mitochondria to help meet the increased energy demands.