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Microscopes (Each one of you is responsible for researching and filling…

- - - - The microscope produces detailed 3D images-
      - It was Manfred Von Ardenne who invented, 1937, a true microscope with high magnification.
        
        link to www.google.co.uk
        
        Advantages of a Scanning Electron Microscope include its wide-array of applications, the detailed three-dimensional and topographical imaging and the versatile information garnered from different detectors.
        SEMs are also easy to operate with the proper training and advances in computer technology and associated software make operation user-friendly.
        This instrument works fast, often completing SEI, BSE and EDS analyses in less than five minutes. In addition, the technological advances in modern SEMs allow for the generation of data in digital form.
        Although all samples must be prepared before placed in the vacuum chamber, most SEM samples require minimal preparation actions.
        
        The disadvantages of a Scanning Electron Microscope start with the cost.
        
        In addition, SEMs are limited to solid, inorganic samples small enough to fit inside the vacuum chamber that can handle moderate vacuum pressure.
        
        The sample chamber is designed to prevent any electrical and magnetic interference, which should eliminate the chance of radiation escaping the chamber. Even though the risk is minimal, SEM operators and researchers are advised to observe safety precautions.
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        Some disadvantages of TEM microscopes are: you need to use a very thinly sliced specimen which can be extremely difficult, the images are only in black and whit so you can see the colours of the cell, the machine is extremely expensive and it can also be very time consuming.
        
        Bacterium through TEM
        
        Electron Microscopy uses a beam of electrons, rather than electromagnetic radiation, to "illuminate" the specimen. A beam of electrons has an effective wavelength on 1nm so can be used to see small sub-cellular structures.
      - TEM microscopy is useful because it magnifies specimems to a much higher degree than an optical microscope. magnification of 10,000 times or more is possible. They are the most powerful microscopes.
      - The main problem with transmission electron microscopes is that specimens must be fixed in plastic and viewed in a vacuum, therefore must be dead. Other problems are that the specimens can be damaged by the electron beam and they must be stained with an electron-dense chemical
- - - - Laser Confocal microscopy uses laser light to control the depth of field, and a pin hole to eliminate out of focus light, thus allowing visualisation of an image in a single horizontal plane.
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  - - - The resolution of a microscope determines the amount of detail that can be seen. Resolution is limited by the diffraction of light as it passes through samples. Diffraction is the tendency of light waves to spread a they pass close to a structure; within the object being studied for example for example. The structures in the specimen being studied are often very close together causing the light to diffract and overlap. Consequently the structures are no longer seen separately. resolution can be increased by using beams of electrons which have a thousandth shorter than light. They still get diffracted but they can be closer together before they overlap.
- - - - Antony van Leeuwenhoek (1632–1723) invented a simple (one-lens) microscope around 1670 that magnified up to 200x and achieved twice the resolution of the best compound microscopes of his day, mainly because he crafted better lenses. While others were making lenses by such methods as squashing molten glass between pieces of wood, Leeuwenhoek made them by carefully grinding and polishing solid glass. He thus became the first to see individual cells, including bacteria, protozoans, muscle cells, and sperm.
        
        Englishman Robert Hooke (1635–1703) further refined the compound microscope, adding such features as a stage to hold the specimen, an illuminator, and coarse and fine focus controls. Until 1800, compound microscopes designed by Hooke and others were limited to magnifications of 30x to 50x, and their images exhibited blurry edges (spherical aberration) and rainbowlike distortions (chromatic aberration). The most significant improvement in microscope optics was achieved in the nineteenth century, when business partners Carl Zeiss (1816–1888) and Ernst Abbe (1840–1905) added the substage condenser and developed superior lenses that greatly reduced chromatic and spherical aberration, while permitting vastly improved resolution and higher magnification.
    - - Compound light microscopes achieve useful magnifications up to 1200x and resolutions down to about 0.25 micrometers. That is, two objects in a cell can be as close as 0.25 micrometers and still detected as separate entities. Such resolution is good enough to see most bacteria and some mitochondria and microvilli.
- - - - Microfilaments: Fiberous filaments made from the protein actin. These fibers are contractile which means they can contract and cause cell movement. This contractile movement is necessary for cells to split apart during mitosis.
      - Microtubules: Polymeric tubes formed from multiple globular tubulin proteins condensing into a large structure. These tubes help with forming and maintaining the overall cell structure, they act as tracks to guide the movement of organelles and vesicles, and they are used as spindle fibres to aid the separation of DNA during mitosis.
      - Intermediate fibres: Fibres which give mechanical strength to the cell and help to maintain their integrity.
      - Centrioles: A component of the cytoskeleton found in most eukaryotic cells apart from some flowering plants and fungi. They are comprised from microtubules. Two centrioles come together to form a centrosome which is responsible for assembly and co ordination of spindle fibres during mitosis. Centrioles are also believed to play a part in the positioning of flagella and cilia when present.
    - - Endoplasmic reticulum: A set of membranes covering flat sacs called cisternae which are connected to the outer membrane of the nucleus. There are two types:
        
        Smooth ER: Responsible for the synthesis and storage of lipids and carbohydrates
        
        Rough ER: Responsible for the production and transport of proteins, and for holding ribosomes on to its surface.
      - Ribosomes: These are structures without membranes which are made out of RNA in the nucleolus. They can be free floating in the cytosol or they can be bound to the ER. Ribosomes are the site of protein synthesis and are found in all cells along with mitochondria and chloroplasts.
      - Golgi apparatus: The golgi apparatus is similar to the smooth ER; it is made from smooth cisternae with no ribosomes. The golgi apparatus' role is to modify proteins and to package them into either secretory vesicles which leave the cell or into lysosomes which remain in the cell.