Biology Unit 1

How does a light microscope work?

It uses a number of lenses. The light from the bulb passes through the condenser lens then through the specimen. The beam of light is focused at the observer lens and then passes through to the eyepiece lens.

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What is the magnification and resolution of a light microscope?

Magnification = x1,500 Resolution = 200nm

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What is magnification?

The degree to which the size of an image is larger than the object itself.

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What is resolution?

The degree to which it is possible to distinguish between two objects that are very close together.

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What is staining?

Chemicals that bind to chemicals in or on the specimen.

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Why is staining needed?

Many biological material is colourless so may not be seen, or it may be hard to distinguish between features, e.g. white blood cells cannot be seen without staining. Some stains combine to specific structures, e.g. Acetic orcein stains DNA red.

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What do they use for staining in light and electron microscopes?

Light - coloured stains or fluorescent dyes. Electron - metal particles or metal salts.

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What are the two types of electron microscopes?

Transmission electron microscope (TEM) and scanning electron microscope (SEM).

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How does a TEM work? What is it's magnification and resolution?

Works y the electron beam passing through the sample, but passes through denser parts less easily, so gives a contrast. The final image is 2D. Magnification = x500,000 Resolution = 0.2nm.

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How does a SEM work? What is it's magnification and resolution?

The electrons do not pass through the sample - the are 'bounced off'. This creates a 3D image. Magnification = x100,000 Resolution = 0.2nm

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What are the advantages and disadvantages of the electron microscope?

Adv: High resolution means higher detailed images. SEM produces a 3d image, which a light microscope cannot do, showing details of contours and tissue arrangements. Disadv: vacuum needed, very expensive, high skill required.

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How does the electron microscope have a higher resolution?

The beam of electrons has a much shorter wavelength than the light microscope

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What is the formula for magnification

Magnification = Image size / Actual size.

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Biology Unit 1

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