The structure that is typically present in both plant and animal cells is:
a. mitochondria
Mitochondria are known as the "powerhouses" of the cell and are found in both plant and animal cells.
The other options can be clarified as follows:
- b. centrioles are primarily found in animal cells and are involved in cell division.
- c. cell walls are present in plant cells (and some fungi and bacteria) but not in animal cells.
- d. chloroplasts are found only in plant cells and some protists, where they are involved in photosynthesis.
So, the correct answer is a. mitochondria.