Module 2: Foundations in biology

2.1-Foundation in biology

2.1.1-cell structure

a)   the use of microscopy to observe and investigate different types of cell and cell structure in a range of eukaryotic organisms








Cost - relatively cheap 
Easy to use 
Portable - can be used in the field and labs
Can study whole living specimens

Limited resolution

Lower magnification

Poor surface view of specimen

Up to x1500 however, some use x2000

Limited resolution

Look at bacteria and used and see the cell as a whole not the individual components

transmission electron

TEMs offer the most powerful magnification, potentially over one million times or more

TEMs have a wide-range of applications and can be utilized in a variety of different scientific, educational and industrial fields

TEMs provide information on element and compound structure

Images are high-quality and detailed

TEMs are able to yield information of surface features, shape, size and structure


Some cons of electron microscopes include:

TEMs are large and very expensive

Laborious sample preparation

Potential artefacts from sample preparation

Operation and analysis requires special training

Samples are limited to those that are electron transparent, able to tolerate the vacuum chamber and small enough to fit in the chamber

TEMs require special housing and maintenance

Images are black and white

x 2 million


0.2 nanometres

o view thin specimens (tissue sections, molecules, etc.) through whichelectrons can pass generating a projection image

Scanning electron

its wide-array of applications, the detailed three-dimensional and topographical imaging and the versatile information garnered from different detectors

Expensive, large and must be housed in an area free of any possible electric, magnetic or vibration interference.

Between x15 to x200 000

0.4 nanometres

Medical profession e.g. observation of fungal filaments for a patient with fungal corneal infection
Biological research




b)   the preparation and examination of microscope slides for use in light microscopy

What are the measurements used for an eyepiece graticule?

Eyepiece units (EPU)

What is an eyepiece graticule?

Fitted with the microscope eyepiece
Transparent with a small ruler

How does an eyepiece graticule work when a specimen is viewed?

The eyepiece graticule is superimposed onto the specimen and then, the specimen can be measured

The eyepiece graticule uses an arbitrary scale - what does this mean?

An arbitrary scale means that it represents different lengths at different magnifications, yet the actual size of the specimen has not changed

What is used to calibrate the eyepiece scale?

A stage graticule - the eyepiece scale must be calibrated for each different objective lens

How is the ruler on the stage graticule divided up?

1mm long - divided into 100 divisions 
each division is 0.01 mm or 10 micrometres


c)   the use of staining in light 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




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