The nuclear envelope surrounding the nucleus separates the chromosomes from the cytoplasm. Animal and plant cells also contain cytoplasm. Perhaps the most important things to be found in cytoplasm are mitochondria. A mitochondrion contains all the enzymes to obtain energy from glucose. They can be seen in detail with an electron microscope.
Mitochondria also contain a bit of DNA which controls how they work.
Some people think that mitochondria look like bacteria. Animal and plant cells also have a cell membrane around them. Cell membranes are very thin, nevertheless they are able to control what can get in or out of a cell. The cell wall is NOT living. The only thing which the cell wall does is to allow very high pressures to build up inside them because of osmosis.