Notes

Biology Revision
When viewing any slide with a microscope, a small square or circle of thin glass called a coverslip is placed over the specimen. It protects the microscope and prevents the slide from drying out when it’s being examined. The coverslip is lowered gently onto the specimen. A mounted needle can be used to hold the specimen in place as the coverslip is lowered. It is important that no air bubbles are trapped underneath. Most cells are colourless. Stains are used to add contrast. Certain stains are also used to stain specific cell structures or cell products. Care must be taken when looking down the microscope if the illumination is too bright. Care when using microscope stains. Care when handling coverslips, microscope slides and mounted needles. The diagram shows the size of three organisms, different cells and other structures. Sizes can be compared using a straightforward calculation. For instance, the length of the leaf cell above is ten times the diameter of a red blood cell. When comparing the size of a bacterium with the Human Immunodeficiency Virus (HIV) different units have to be converted to be consistent. Therefore the length of the bacterium is = 10 times that of the bacterium. Throughout their development, the magnification of light microscopes has increased, but very high magnifications are not possible. The maximum magnification with a light microscope is around ×1500. Throughout the development, the magnification of light microscopes increase, but very high magnifications are not possible. The maximum magnification with a light microscope is around ×1500. Nucleus contains genetic material [DNA] .