Transmission electron microscope-

Limits:

· The whole system must be in a vacuum and therefore living specimens cannot be observed.

· A complex ‘staining’ process is required and even the image is only in black and white.

· The specimen must be extremely thin.

· The image may contain artefacts. Artefacts are things that result from the way that the specimen is prepared.

The electron microscope suffers similar limitations besides from the fact that the specimen does not need to be extremely thin as the electrons do not penetrate.

Magnification= Size of image/Size of object.

Structure of an epithelial cell- The nucleus:

· The Nuclear envelope is a double membrane that surrounds the nucleus. Its outer membrane has continuous with the endoplasmic reticulum of the cell and often has ribosomes on its surface. Controls the entry and exit of materials.

· Nuclear pores allows the passage of larger molecules e.g. the messenger RNA.

· Nucleoplasm is the jelly like material that makes the bulk of the nucleus.

· Chromatin is the DNA found within the nucleoplasm. This is the diffuse form the chromosomes take up when the cell is not dividing.

· The Nucleolus is a small spherical body within the nucleoplasm. It manufactures ribosomal RNA.

The nucleus’s functions are: Act as a control centre of the cell through the production of mRNA and hence protein synthesis.

Retain the genetic material of the cell in the form of DNA or chromosomes.

Manufacture ribosomal RNA and ribosomes.

	Erstellt von Alex_Daines vor mehr als 10 Jahre

Notiz am Microscopes and cell structure, erstellt von Alex_Daines am 27/04/2014.