Module 1 Biology AS 1.1-1.17

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  • Created by: Josh
  • Created on: 11-12-11 13:11

Living organisms

Limitation and advantages of Light microscopes
Magnification- The number of times greater an image is than the object 
Resolution- The ability to distinguish two seperate points as distinct from each other

Light microscope
Magnification- Most light microscopes are capable of magnification up to a maxiumum of x1500
Resolution- The maximum resolving power using light is 200nm. Two objects can be distinguished only if light waves can pass between them.

Staining- Coloured stains are chemicals that bind to chemicals on or in the specimen. Some stains bind to specific cell structures. Acetic orcein stains DNA dark red. Gentain violet stains bacterial cell walls
Sectioning- Specimens are embedded in wax. Thin sections are then cut without distorting the structure of the specimen. This is praticularly useful for making sections of soft tissue, such as brain.

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Limits of resolution
Human eye is 100 micro meters
light microscope is 200 nano meters
electron microscope is 0.20 nano meters

Magnification and micrographs
actual size= image size/ magnification

This means that it is possible to work out either the magnification of a micrograph or drawing, or the actual size of the cell or part of the cell shown in the micrograph or drawing. 

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Cells and Living processes

Each type of organelle has a specific role within the cell this is called division of labour.

Cells contain a network of fibres made of protein. These fibres keep the cell's shape stable by providing an internal framework called the cytoskeleton.

There are other fibres known as microtubules. These are cylinders about 25nm in diameter. They are made of protein called tubulin. Microtubules may be used to move a microorganism through a liquid, or to waft a liquid past the cell.

Other proteins present on the microtubules move organelles and other cell contents along the fibres. This is how chromosomes are moved during mitosis. It is how vesicles move from the endoplasmic reticulum to the Golgi apparatus. These proteins are known as microtubule motors. They use ATP to drive these movements. 

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