Both plant and animal cells have mitochondria because they both carry on respiration. Mitochondria are known as the powerhouses of the cell, as they play a crucial role in converting the energy stored in food into a usable form, ATP (adenosine triphosphate), through the process of cellular respiration.
While plant cells also contain chloroplasts for photosynthesis, which allows them to convert sunlight into energy, they still rely on mitochondria to break down glucose and release energy when needed, especially in the dark or during non-photosynthetic activities. Animal cells, on the other hand, do not perform photosynthesis and depend solely on mitochondria for energy production. Therefore, it is the process of respiration that necessitates the presence of mitochondria in both types of cells.