A cell is covered by the cell membrane in the cells of animals, some protists and some monerans), or by the cell wall in plants. What the cell itself contains will depend on what organism it is part of, but it could include a variety of features all with different functions, including organelles, cytoplasm, chloroplasts, mitochondria, a nucleus, ribosomes, vacuoles, endoplasmic reticulum, and in instances where the cell has a wall, the cell membrane itself.