7.1 Using a light microscope. . . . 61 7.2 Cell structure . . . . . . . . . 63 7.3 Cell structure and function . . . 66 7.4 Cell organisation . . . . . . . 68 7.5 How society influences scientific research . . . . . . 70
Why it matters
Understanding the cell helps us to understand how living things work as they are the building blocks of all living things.
Cells are the building blocks of all living organisms. All cells come from other cells. This is called the continuity of life. Some living things are made up of only one cell (unicellular), such as bacteria and yeast, other living things are made up of many cells (multicellular), such as a tree or a human being. In 1663 Robert Hooke, an English scientist, was the first person to describe the appearance of cells. He made his observations using a microscope. The microscopes that were used at that time were very simple. In fact, scientists were only able to see the outside of cells. The microscopes in use today are much more powerful and scientists are able to observe the outside and the inside of cells in great detail.
Fig. 1 Microscopes such as a scanning electron microscope can magnify a sample many thousands of times.
1. Eyepiece 7.1 Using a light microscope
A light microscope has five main parts: 1. The eyepiece: for looking through; it magnifies the sample. 2. The objective lens: above the stage, it also magnifies the sample. 3. The stage: where you place the slide holding your sample. 4. The coarse focus knob: to focus the sample you are looking at. 5. The fine focus knob further sharpens the image.
2. Objective lens
3. Stage
The eyepiece usually magnifies by 10 (×10). The objective lenses magnify by four (×4), by 10 (×10) and by 40 (×40). At high power the microscope will magnify the sample 10 x 40 = 400 times.
4. Coarse focus knob
5. Fine focus knob
Fig. 2 A light microscope. 61
LO 1 Biological World strand LO 10 Nature of Science strand
Light microscope A type of microscope which uses white light and a system of lenses to magnify small samples.
