- Cell Structure
- All living organisms are made of a cell or a collection of cells. Cells and their contents are usually measured in micrometres. 1 micrometre is one thousandth of a millimetre
- Specimens to be viewed using a microscope are usually stained to make parts of them look darker or different colours
- Plant and animal cells are eukaryotic cells, with a nucleus surrounded by an envelope. The nucleus contains the DNA, in the form of chromosomes All cells are surrounded by a partially permeable membrane.
- Plant and animal cells contain ribosomes for protein synthesis, endoplasmic reticulum for the storage & transport of substances made in the cell, golgi apparatus for processing & packaging proteins, lysosomes containing digestive enzymes & mitochondria to produce ATP by aerobic respiration.
- Bacteria are prokaryotic cells, which do not have a nucleus. Their DNA is not associated with histones, and is present as a circular strand. It is attached to the plasma membrane. Prokaryotic cells lack complex membrane-bound organelles such as mitochondria. They have similar ribosomes than eukaryotic cells. They always have a cell wall but it is made of peptidoglycan not cellulose
- Animal cells contain a pair of centrioles, which organise the the microtubules in the cell, e.g. when forming the spindle during cell division. Animal cells may also have cilia or flagella.
- Microtubules & microfiliments form the cytoskeleton, holding the cell in shape & helping to move organelles around in the cell