All living organisms are made of cells. There are two main cell types: eukaryotic and prokaryotic. Eukaryotic cells include animal and plant cells. Their genetic material is enclosed inside a nucleus, and they contain membrane-bound structures such as mitochondria.
Prokaryotic cells are bacteria. They are much smaller than eukaryotic cells and have no nucleus or other membrane-bound organelles. Their genetic material is a single circular loop of DNA lying free in the cytoplasm; some also contain small rings of DNA called plasmids. Bacteria have cytoplasm, a cell membrane, a cell wall and ribosomes, and some have a flagellum for movement.
Animal cells contain a nucleus (contains DNA and controls cell activities), cell membrane (controls what enters and leaves), cytoplasm (where many chemical reactions occur), mitochondria (site of aerobic respiration), and ribosomes (where proteins are made).
Plant cells contain all of these structures. They also have a cellulose cell wall for strength and support, chloroplasts containing chlorophyll to absorb light for photosynthesis, and a large permanent vacuole filled with cell sap that helps keep the cell turgid.
Do not confuse a plant cell wall with a bacterial cell wall: both provide support, but a plant cell wall is made from cellulose. Plant and animal cells are eukaryotic because their DNA is enclosed in a nucleus; bacterial cells are prokaryotic because their DNA is not enclosed in a nucleus.