In order to study the structures that make up the tissues and cells of organisms, it is necessary to use various magnifying equipment. The light microscope can be used to look at details as small as the organelles that make up the internal structures of cells. Typically they provide magnification up to x1000. Typical microscopes in school magnify to x400 to x500.
A light microscope projects a beam of light from a mirror, or a lamp, through a small hole in the stage. On the stage, a sample is placed on a slide, normally covered with a coverslip to protect the sample. The light is then magnified, first by the objective lens and then by the eyepiece lens. The objective lenses come in 3 or 4 magnifications and can be turned to change the lens.
The total magnification of the sample is calculated from multiplying the magnification power of the eyepiece lens with that of the objective lens in use. Eyepiece x10 and objective x40 gives x400 magnification.
The field of view (how much of the sample can be seen at any one time), gets smaller as the magnification increases.
- Details of the set-up and use of the light microscope are contained in section CS7: Practical Skills, of the full course.
The use of light as a means to provide the magnification has some limits. The resolution, how clear the image is, reduces as the magnification increases, and the lens can start to add colour distortion (known as chromatic aberration). This means that there is a practical limit to how much magnification can be achieved with a light microscope, x1500 is about as high as can reasonably be achieved.
Electron-microscopes, however, use a beam of electrons to scan the surface of objects and produce a much higher magnification and resolution. They can produce images up to x10 million magnification. They cannot, however, sample living tissue as the sample is normally coated in metal, often gold then placed in a vacuum.
Electron microscope image of red blood cells.
Plant and animal cells are examples of eukaryotic cells as they both contain a nucleus carrying the genetic material. Simpler cells of bacteria and other single-celled organisms do not contain a nucleus and are known as prokaryotic cells.
The key difference between the eukaryotic and the prokaryotic cells is the presence or absence of the nucleus, prokaryotes also have a distinctive plasmid.
- Which of the following is not found in an animal cell?
- cell wall
Explanation: Only plants contain a rigid cell wall on the outside of the cell.
- What is the function of the mitochondria in eukaryotic cells, and what do they contain to help them perform this function?
- Your answer should include: organelles are responsible for respiration / they contain enzymes to help them perform this function