Explain With Aid Of A Diagram The

Working Of The Electron Microscope Essay, Research Paper

The diagram below shows a picture

of an electron microscope. This is a type of microscope that makes use of a

beam of electrons rather than visible light. Because the wavelength of

electrons is much smaller than the wavelength of visible light, an electron

microscope not only gives a high magnification but it also has high resolution.

This means that details can be seen clearly. An electron microscope is very

similar to a light microscope in the ways in which it works but, instead of

using glass lenses to focus a beam of light, it uses magnets to focus a beam of

electrons. Electrons are very small so they are scattered if they hit molecules

in the air. Because of this they must travel through a vacuum. Specimens that

are to be examined must be cut into very thin sections, and these must be

treated so that they can be examined in these conditions. The variety of

chemical processes that are carried out in this preparation may change the

appearance considerably. Features which have been introduced in this way are

known as artefacts and care needs to be taken in interpreting electron

micrographs because of the possible presence of artefacts. The main differences

between a light microscope and an electron microscope are shown in the table

below.FEATURE?????????????????? LIGHT MICROSCOPE????????????????????? ELECTRON

MICROSCOPESource of illumination??? Visible light?????????????????????????????????????????? Beam of electrons Method of focusing?????? Glass lenses????????????????????????????????????????? Magnets Specimens which can ?? Live or dead???????????????????????????????????????? Dead Be examined Magnification??????????????? Student microscopes magnify up?????????? Up to 500000 times ??????????????????????????????????? To

about 400 times but the ??????????????????????????????????? Maximum

magnification that can ??????????????????????????????????? Be

achieved with a light ??????????????????????????????????? Microscope

is about 1500 times Resolution??????????????????? About 0.2 ??????????????????????????????????????????? About

1?? or 0.001??? .(B) Outline

the structure and functions of the following organelles: endoplasmic reticulum. ??????????? A network

of membranes found in the cytoplasm of a cell. It consists of a complex system

of pairs of membranes arranged parallel to each other enclosing flattend,

fluid-filled spaces. These membranes may be covered with ribosomes, in which

case they form rough endoplasmic reticulum. The ribosomes produce proteins

which are transported through the spaces between the membranes. Smooth endoplasmic

reticulum does not have ribosomes on its surface. Its main function is the

production and transport of lipids. Golgi apparatus ??????????? An

organelle which is responsible for the processing and packaging of substances

produced by a cell. The golgi apparatus consists of a series of flattened sacs,

each one enclosed by a membrane. These sacs are continually being formed on one

side and pinched of to form small vesicles at the other. Mitochondria ??????????? A

cell organelle in which the biochemical reactions associated with aerobic

respiration take place. Each mitochondrion is surrounded by an envelope

consisting of two membranes. The inner one is folded to form structures

cristae. Numbers of mitochondria vary considerably from cell to cell. Cells

which contain particularly large amounts of these organelles usually require

large amounts of ATP. Ribosomes ??????????? A very

small organelle which plays an important part in making proteins. It is made of

a mixture of protein and a special sort of RNA called ribosomal RNA. During

protein synthesis a molecule of messenger RNA (mRNA) carries the genetic code

for a particular protein from the nucleus into the cytoplasm of the cell.

Ribosomes now move along this mRNA molecule. This results in amino acids being

assembled in the correct order to form a molecule of the protein concerned.

There are two basic types of ribosome. Those found in the cytoplasm of

eukaryotic cells are slighlt larger than those found in the prokaryotic cells. Lysosomes ??????????? An

organelle containing digestive enzymes. These enzymes are seperated from the

rest of the cell contents by the membrane which surrounds the lysosome. This is

essential otherwise these enzymes would digest the proteins and lipids normally

found in the cell and destroy them. Lysosomes are usually associated with

animal cells where they have a number of different functions. Chloroplasts ??????????? A

chlorophyll containing organelle found in the cells of plants and algae. It is

where photosynthesis takes place. The chloroplasts found in plant cells are

small, flattened discs, each about five micrometers in diameter. They are found

in the cytoplasm but can change their position in response to differences in

light intensity. Chlorop

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