All living things are made of cells. Animal cells contain: nucleus (genetic material), cell membrane (controls entry/exit), cytoplasm (where reactions happen), mitochondria (respiration), ribosomes (protein synthesis).
Plant cells also have: cell wall (cellulose, support), permanent vacuole (cell sap), chloroplasts (photosynthesis).
Animal and plant cells are eukaryotic: their DNA is enclosed in a nucleus and they contain membrane-bound organelles. Bacteria are smaller prokaryotic cells: they have no nucleus or other membrane-bound organelles. They have a cell wall, cell membrane, cytoplasm, ribosomes, a single circular DNA molecule, and may also have plasmids and flagella.
Microscopy: Magnification = Image sizeActual size (M = I/A). Light microscopes can magnify living cells and show larger structures. Electron microscopes have much higher magnification and resolution, so their development allowed scientists to see much smaller sub-cellular structures, such as ribosomes and the internal details of mitochondria and chloroplasts. This new evidence improved cell models and understanding over time.