Unicellular - One cell (e.g. Bacteria)
Mulitcellular - More than one cells
Light microscopes use glass lenses to refract light rays and produce a magnified image of a object.
Slide (containing organism) is placed on a stage, light is focused onto specimen by a condenser lens.
Light passes through the specimen and is captured and refracted by objective lens.
Light rays now travel upto the eye piece. This produces the final image, which falls on the retina of your eye.
Most specimen are colourless so need to be stained to be able to be seen.
Different parts of cell take in more staining than others
Methylene Blue is taken up by nucleus most.
Light Microscope Diagram
Microscopes make a specimen look a lot larger than it actually is. This is magnification.
The equation for working out magnification is:
Resolution - the ability to distuingish betwen two points easily. It is the degree of detail that can be seen
There is only so much detail a light microscope can go into until the resolution goes.
To get better resolution we can use a electron microscope. We can fire elctron beams as it has a much shorter wavelength than light. They have a better resolution which is 400x better than light microscopes.
Transmission Electron Microscopes (TEM)
Works in a similar way to a light microscope, it passes electrons through a specimen.
Specimens need to be cut thinly and stained
Metal stains are used such as Iron or Osmium . Ions are large and positively charge.
The negative charged electrons do not pass through them, and so do not arrive on screen. The screen stays dark in these area, so the areas which have taken up stains look darker than other areas.
Transmission Electron Microscopes (TEM) - Diagram
Scanning Electron Microscopes (SEM)
This microscopes works by bouncing electron beams of the surface of an object.
Produce a 3D image. However the colours produced are black, gray and white. However colours can be changed by a computer.
Provides images that can magnified to the same level as the TEM.
Object be examined is sometimes have gold splattered on them because gold has large atoms from which electrons can bounce off, giving a clear image of the surface of the object.
Scanning Electron Microscopes (SEM) - Diagram
Appearance of Cells using Microscopes
Light microscope produces a photomirograph
Electron microscopes can view smaller structures in higher detail compared to light microscope. The structure produced is called the ultrastructure.
Ultrastructure of a animal cell
Ultrastructure of a plant cell
Structure and Function of Organelles
See green booklet in folder
Prokaryotic means 'before nucleus'
Prokaryotic cells are cells which dont have a nucleus.
Prokaryotics DNA lies free in the cytoplasm. Circular DNA.
Prokaryotic cells dont have mitochondria, cholorplasts and endoplasmic reticulum.
They have ribosomes and have a cell wall (made up of peptidoglycan fibres).
Prokaryotic Cells - Diagram