The development of microscopes
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 Ă—1,500. This means that the microscopes can make the image look 1,500 times bigger than the actual object.
The limits of the light microscope
The magnification of a microscope is not the only factor that's important when viewing cells. The detail that can be seen is also important.
The ability to see greater detail in an image depends on the resolution or The ability to see two points as two points, rather than merged into one. . This is the ability to see two points as two points, rather than merged into one.
Think about a digital photo. It can be enlarged, but over a certain size, you won't be able to see any more detail. It will just become blurry.
The resolution of a light microscope is around 200 nm. This means that it cannot distinguish two points closer than 200 nm. One nm, or nanometre, is one billionth of a metre.
The electron microscope
Electron microscopes use a beam of electrons instead of light rays.
There are two types of electron microscope:
- The scanning electron microscope (SEM) has a large The distance between the nearest and farthest objects in focus. so can be used to examine the surface structure of specimens. SEMs are often used at lower magnifications.
- The transmission electron microscope (TEM) is used to examine thin slices or sections of cells or A group of similar cells that carry out the same function, eg muscle tissue..
TEMs have a maximum magnification of around Ă—1,000,000, but images can be enlarged beyond that photographically. The limit of resolution of the TEM is now less than 1 nm.
The TEM has revealed structures in cells that are not visible with the light microscope.
Visualising sub-cellular structures
Structures that are found inside a cell, such as the nucleus, are called Any structure that is found inside of a cell.. If the sub-cellular structure has a membrane surrounding it then it is also known as an The name given to a membrane bound compartment with a specific function in animal, plant and fungal cells.. Some sub-cellular structures can be studied easily using a light microscope because they are quite large, for example the nucleus inside an animal or plant cell. However, there are many more sub-cellular structures in animal and plant cells and most of these cannot be viewed using a light microscope because the The amount that an image of something is scaled up when viewed through a microscope. and The fineness of detail that can be seen in an image - the higher the resolution of an image, the more detail it holds. In computing terms, resolution is measured in dots per inch (dpi). of the light microscope is too low.
Once the electron microscope had been developed, scientists could find out much more about sub-cellular structures. Often, the more scientists know about the structure of something, the more they can work out about how that thing functions. The development of the electron microscopes therefore helped scientists to learn about the sub-cellular structures involved in Respiration that requires oxygen. called Structures in the cytoplasm of all cells where aerobic respiration takes place (singular is mitochondrion).. The scientists developed their explanations about how the structure of the mitochondria allowed it to efficiently carry out aerobic respiration.
Another organelle that has been studied in much more detail since the development of the electron microscope is the Contains the green pigment chlorophyll; the site of photosynthesis.. Chloroplasts are found in plant cells and are used by the plant to carry out A chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis. Algae subsumed within plants and some bacteria are also photosynthetic. so that the plant can make its own source of glucose to be used in respiration. Scientists have much more knowledge and understanding of how a chloroplast can carry out photosynthesis because they have been able to use electron microscopes to look at them in lots of detail due to the high magnifying power of an electron microscope.