1. All living organisms are made of cells.

2. Our understanding of cell structure and function has gone hand in hand with developments in microscopy and its associated techniques.

3. Light microscopy revealed the diversity of cell types and the existence of the major organelles: nucleus, mitochondrion and, in plants, the vacuole and chloroplast.

4. The electron microscope revealed the detailed structure of the larger organelles and resolved the cell ultrastructure, the fine detail at the nanometer scale.

5. There are two types of cells, prokaryotes and eukaryotes.

6. Prokaryotic cells have very little visible internal organization. They usually measure 1-2 /m across.

7. Eukaryotic cells usually measure 5-100 /m across. They contain a variety of specialized internal organelles, the largest of which, the nucleus, contains the genetic material.

8. The endosymbiotic theory proposes that some eukaryotic organelles, such as mitochondria and chloroplasts, originated as free-living prokaryotes.

9. The cells of plants and animals are organized into tissues. In animals there are four tissue types: epithelium, connective tissue, nervous tissue, and muscle. Plants are formed of epidermis, cortex, and vascular tissues.

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