Cells, Exchange and Transport

Cells
(a) state the resolution and magnification that can be achieved by a light microscope, a transmission electron microscope and a scanning electron microscope;
Resolution Magnification
Light microscope 200nm x1,500
Transmission Electron Microscope 0.1nm x500,000
Scanning Electron Microscope 0.1nm X100,000

(b) explain the difference between magnification and resolution;
Magnification is the degree to which the size of an image is larger than the image itself.
Resolution is the degree to which it is possible to distinguish between two objects that are very close together.

(c) explain the need for staining samples for use in light microscopy and electron microscopy;
A lot of biological material inside a cell isn’t coloured, so it might be difficult to distinguish between different features. Coloured stains are used to stain specimens for use with the light microscope. Chemicals which bind to other chemicals on, or in, the specimen, which allows the specimen be to seen. Some chemicals bind to specific structures, such as Acetic orcein staining DNA red. Electron micrographs start off black and white, with the colour being added by a specialised computer program afterwards. (d) calculate the linear magnification of an image;
Image size =Actual size x Magnification

(e) describe and interpret drawings and photographs of eukaryotic cells as seen under an electron microscope and be able to recognise the following structures:
Nucleus,
Largest organelle.
Nucleolus,
Dense, spherical structure inside nucleus
Nuclear envelope,
Surrounds the nucleus
Rough and smooth endoplasmic reticulum (ER),
Continuous with the nuclear envelope. RER is studded with ribosomes, SER is not.
Golgi apparatus,
Stack of membrane-bound flattened sacs
Ribosomes,
Tiny. Some are in the cytoplasm and some are bound to the RER