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AS Biology
Module 1
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Bits and Bobs
• Text books
• Information booklets
• What to expect from AS biology.
• HOMEWORK 1: read through the 2 booklets.
Cells and the microscope.
What do animal and plant cells look
like and how can we work out their
Draw and fully label an animal cell and a plant cell. State
what each organelle (part) is for.
How do we know what they look like?
History of cells
Resolution – the degree to which it is possible to
distinguish clearly between 2 objects.
Magnification – how many times bigger an
object appears in relation to real life.
Light microscopes and resolving
• The maximum resolving power of a light
microscope is 200nm.
• Particles can be seen as separate if they are over
0.5 the wavelength of light, apart.
• We can use it to observe microorganisms such as
Euglena and Daphnia, thin sections of other
organisms and samples of cells.
• Wait … what the hell is a nm?!
Complete “magnification and
Scientific measurements
Text book page 6.
μm = micrometer = 1/1000 000 of a meter.
or 1/1000 of a mm
nm = nano meter = 1/1000 000 000 of a meter
or 1/1000 of a μm
Nano is smaller than micro.
Q: if the human eye an resolve 100 μm and the light
microscope can resolve 200nm , which can see smaller things
and why?
Complete “units of measurement”
• First half
Cells and the microscope.
How can I work out the size of a
microscopic sample?
1) Label your light microscope diagram.
2) work out the overall magnification when using an
objective lens of x40 and an eye piece lens of x10.
Working out the size of microscopic
samples .
• A quick Recap
To work out the size of a microscopic
sample, you use a graticule
Glossary word- a small ruler etched onto an eye
piece lens.
Amoeba under microscopes
X10 objective
x40 objective
Calibrating the
The eye piece graticule will
always stay the same.
The stage micrometer has
been zoomed in on
The micrometer is 1mm
long and has 100 divisions.
Each division is 10 μm.
Converting eye piece units to μm
Q: if you are using a x 4 objective lens and a x10
eye piece lens, what is the overall
Converting eye piece units to μm
at x 40
1mm = 40 epu.
Each division on the
micrometer = 0.01mm or 10
The whole micrometer =
1000 μm
So 1 epu is = to 1000/40
= 25 μm
40 epu
At x 100
1mm = ____ epu
100 epu
Each division on the
micrometer = 0.01mm or 10
The whole micrometer =
1000 μm
So 1 epu is = to _____/____
= ___ μm
Magnification and micrographs
• When given a drawing/micrograph, you can
work out how big things are in real life, using
the following relationship. All measurements
need to be in μm
Complete the questions on
Using a light microscope
How can I draw what I see under a microscope?
Label your diagram of the light
1) What are the 2 lenses in a light microscope?
2) Describe the journey of light through the
The light microscope
• Has a maximum resolution of 200nm – half
the wave length of light.
Observing and drawing cells.
• Follow the schedule for the plant cell so you
have a sample on your microscope.
Read the information on biological drawings.
Repeat with animal cells.
Stains are coloured chemicals that are used to bind to certain parts
of cells that might be clear, in order for them to be visualised.
Colours produced
Methylene Blue
Stains acidic cell parts
Acetic orcein
stains chromosomes and
connective tissue
Dark red
Stains alkaline parts of the
Gentian Violet
Stains bacterial cell walls
Iodine solution
Stains carbohydrates
Brown / black
Light green
Thin samples are needed for microscopy. This is
so that the light can get through.
TO see inside larger specimens, sections must be
cut – a bit like with one of those ham slicers on
the deli counter.
The sample is embedded in wax to stop it from
distorting, set and then sliced.
What are the differences and uses of
the 3 main types of microscope?
How many parts of an animal cell can you name.
There are at least 11 you need to know!
Did your animal cell look like this?
Modern Microscopes
• Light microscope – useful for basic microscopy
and in schools, but low resolution.
• Electron microscopes – use beams of
electrons so the resolution is as good as
• What is that in mm?
Transmission Electron Microscope –
Max magnification x 500’000
Electron beam passed through
a very thin sample.
Electrons pass through thick
bits less easily so give contrast.
Final image black and white.
What do you notice about these,
compared to light microscope images?
Scanning Electron Microscope – SEM
Max magnification x 100’000
Electron beam directed onto a
Electrons bounce off and
produce a 3D image of the
Final image black and white.

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