Cell Structure

a)   State the resolution and magnification that can be achieved by a light microscope, a transmission electron microscope and a scanning electron microscope;

 Name                                                             Resolution              Magnification

Light Microscope                                              200nm                                  x1,500

Transmission Electron Microscope                   0.1nm                                 x500,000

Scanning Electron Microscope                         0.1nm                                  x100,000

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b)   Explain the difference between magnification and resolution;

Magnification- The degree to which the size of an image is larger than the actual image

Resolution- 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;

Most biological material inside of a cell is not coloured, therefore making it harder to distinguish between different features. Coloured stains are used for use with light microscopes, as chemicals bind to other chemicals on (or in) the specimen, allowing certain features to be seen. Some chemicals can bind to specific structures, for example Acetic orcein stains DNA red.

Electron micrographs begin with a black and white image, then add colour using a specialised computer program afterwards.

d)   Calculate the linear magnification of an image;

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 present in the eukaryotic cell, holds genetic material.

Nucleolus;

Is a dense, spherical structure inside of the nucleus.

Nuclear Envelope;

Surrounds the nucleus, has nuclear pores for mRNA to move out of.

Rough and smooth endoplasmic reticulum (ER);

Continues around the nuclear envelope. RER is studded with ribosomes, SER isn’t.

Golgi Apparatus;

Stack of membrane-bound flattened sacs

Ribosomes;

These are tiny, with some in the cytoplasm and others bound to the RER.

Mitochondria;

Spherical or sausage shaped, with a double membrane.

Lysosomes;

Spherical sacs with a single membrane.

Chloroplasts;

Found only in plant cells, with two membranes containing Thylakoids.

Plasma membrane;

Phospholipid bilayer.

Centrioles;

Small tubes of protein fibres, with a pair of them next to the Nucleus in animal cells.

Flagella and cilia;

Hair-like extensions projecting from the surface of a cell.

f)   Outline the functions of the structures listed in (e);

Nucleus;

Holds the cells genetic material in the form of DNA, which contains the instructions for protein synthesis.

Nucleolus;

Makes ribosomes and RNA which pass into the…