Chloroplasts are organelles responsible for photosynthesis, the process by which plants and some other organisms convert light energy into chemical energy. They contain chlorophyll, the green pigment that captures light energy. However, animal cells do not contain chloroplasts because animals do not carry out photosynthesis; they obtain energy by consuming other organisms.
In contrast, other options like the cell wall, which provides structure and protection, is found in plant cells but not animal cells. While animal cells do have a nucleus, which houses DNA and regulates cellular activities, and vacuoles, which are used for storage and maintaining cell turgor, chloroplasts are specifically absent in animal cells, making them the correct choice in this question.