Cell theory: The basic unit of structure and function of all living organisms is the cell.
Virchow’s theory: All cell arise from pre-existing cells by cell division.
| Animal cells | Plant cells | Plasma membrane | Yes | Yes | Nucleus | Yes | Yes | Cytoplasm | Yes | Yes | Mitochondria | Yes | Yes | Golgi apparatus | Yes | Yes | Centriole | Yes | No | Cell wall (joined to other cells by plasmodesma) | No | Yes | Large central vacuole | No | Yes | Chloroplasts (surrounded by tonoplast) | No | Yes |
* 1000m = 1mm * 1000nm = 1m
Magnification: Number of times larger an image is compared with the real size of the image.
Magnification= size of image actual size of specimen
Resolution: the ability to distinguish between two separate points.
* An increase in magnification does NOT necessarily mean an improvement in resolution. Ex. A light microscope has a max resolution of 200nm meaning that if two points are closer than 200nm they can’t be distinguished as separate no matter how large the magnification.
The electron microscope
When a metal becomes very hot, some of its electrons gain so much energy that they escape from their orbits. They behave like electromagnetic radiation. They are good forms of radiation because 1. Their wavelength is extremely short, 2. Since they are negatively charged they can be focused easily using electromagnets. (That’s why X rays aren’t very good because they can’t be focused easily.) Electron microscopes must be in a vacuum (to prevent electrons colliding with air molecules and scattering), and only dead material can be examined ( because water boils at room temperature in a vacuum so specimen must be dehydrated.)
Transmission electron microscope (TEM): the beam microscope is passed through the specimen before being viewed. Only those that pass through the specimen are seen and therefore allow us to see through the specimen and cells. 2D image.