GCSE Biology | Microscopy
Of all the techniques used in biology microscopy is probably the most important. The vast majority of living organisms are too small to be seen in any detail with the human eye. Cells and their organelles can only be seen with the aid of a microscope.
Of all the techniques used in biology microscopy is probably the most important. The vast majority of living organisms are too small to be seen in any detail with the human eye, and cells and their organelles can only be seen with the aid of a microscope.
A Light (or Optical) microscope uses light waves
Magnification: is how much bigger a sample appears to be under the microscope than it is in real life.
Resolution: Is the ability to distinguish between two points on an image i.e. the amount of detail or clarity. The resolving power of a particular microscope depends on the wavelength or form of radiation used.
Microscopy: Simple magnification calculations
When Working out simple microscopy calculation use the "IAM" Triangle
When you need to work out Magnification:
If you are given the Image size and the Actual size you need to work out the Magnification (how much bigger the image size is compared to its Actual size).
Use the "IAM" Triangle like this: -
Cover the "M" and use Image size divided by the Actual size.
When you need to work out the image size (i.e. the diagram/picture):
If you are given the Actual size of an object and the Magnification used, you are being asked to work out the Image size (this could be the diagram /photograph measured).
Use the "IAM" Triangle like this: -
Cover the "I" and use Actual size given Multiplied by the Magnification given.
When you need to work out the Actual size of the object (e.g. cell):
If you are given the Image size (or asked to measure it!) (e.g. a photograph or drawing) and you are given the Magnification used, you are being asked to work out the Actual size of something.
Use the "IAM" Triangle like this.
Cover the "A" and use image size given
divided by the Magnification given.
Here is a common example using the IAM triangle and very commonly asked question in both GCSE and A-Level Biology!
The diagram below shows Escherichia coli (E. coli) bacterium at a magnification of 20 000x.
Common questions at GCSE (and A-Level!) are:
"What is the actual length of the bacterium from A to B in micrometers (µm)?"
Remember to be awarded full marks you must always show your working out!
So how do you answer this very common (GCSE biology and A-Level Biology) question?
1. Measure the distance from A to B in mm
2. Use the IAM Triangle to calculate the actual length...
(Image) 150mm / (Magnification) 20000 = (Actual size) 0.0075 mm
3. Convert millimeters (mm) to micrometers (µm). Remember millimetres (mm) and micrometers (µm) differ by a factor of 1000, that is 1µm is 1000 times smaller than a 1 mm!
So, to convert millimetres (mm) into micrometers (µm) just multiply by 1000 like this: -
0.0075mm x 1000 = 7.5µm (micrometers)
Answer: 7.5µm
So, there it is your step by step 'working out' and your final answer must be clearly stated (or shown as it is above.
Download the lesson resources
GCSE Biology - Lesson 02 Light Microscopes and the IAM Triangle.pdfGCSE biology Cells - Worksheet 2.1 - Light Microscops.pdfGCSE biology Cells - Worksheet 2.2 - The Size of Things.pdf