Microscopy

Cell theory states:

Both animal and plant tissue is made of cells

Cells are the basic unit of all life

Cells only develop from existing cells

Light microscopes usually have 2 lenses: an objective lens and an eyepiece lens. This allows more magnification than with one lens.

Stains are often used in microscopy to be able to view certain organelles more easily (increased contrast).

Stains can be used to differentiate between very similar organisms. For example, without a stain, gram-positive and gram-negative bacteria appear to be the same. When a staining technique is used, however, they are differently coloured and can be distinguished from one another.
Crystal violet and iodine are added to the specimen, which is then washed with ethanol. This washes away the stain of the gram-negative bacteria, as their cell walls are much thinner. This causes them to appear pink, whereas gram-positive bacteria appear purple.

Scientific diagrams must be drawn using smooth, continuous lines and without shading. When labeling them, the label lines should not cross each other and they should not have arrow heads.

To calculate magnification from image size and actual size, use this formula:   

Magnification  =  size of image ÷ actual size

e.g. A cell appears to be 5mm in diameter, but it is actually 10µm. What is its magnification?

5mm = 5000µm     5000÷10 = 500x magnification

The two types of electron microscope are transmission electron microscopes (TEM) and scanning electron microscopes (SEM).

TEM:
A beam of electrons passes through a specimen and focuses to produce an image. Resolving power = 0.5nm

SEM:
A beam of electrons bounces off the surface of a specimen to produce a 3D image. Resolving power = 3-10nm

TEM (Viruses):

SEM (blood):