This is part of the PowerPoint that covers section 1.1 in the Cambridge Pre-U Biology course. The full PowerPoint covers the following topics: Microscopy, cell membrane structure, transport across membranes, cell organelles.

1. MAKING SENSE OF
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• The smallest unit of life is one cell big.
• This means that cells are the key to life.
• A single cell has everything required for life.
• If we look inside cells we can see that they are
compartmentalised into different sections which
each have their own role.
• In this section we will look at the structure of
eukaryotic cells and also how to observe them using
microscopes.

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• All cells can be split into two categories.
Prokaryotic Cells Eukaryotic Cells
• The major difference is that prokaryotes don’t have a nucleus
whereas eukaryotes do.
• We will look at eukaryote cell structure first.

4. MAKING SENSE OFMAKING SENSE OF
Microscopy
Cell membrane structure
Transport across membranes
Organelles
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• In 1665 biology changed forever because the first
microscope was evented.
• It opened up a whole new and exciting microscopic
world which allowed scientists to study cells and very
small organisms.
• Ever since then the microscope has developed and
today it is a sophisticated piece of technology.
• You will learn about two types in this section of the
course: light microscopes and electron microscopes.
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a) Discuss the relative advantages of light and electron
microscopes.
b) Explain and distinguish between resolution and
magnification with reference to light microscopy
and electron microscopy.

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• In 1665 a man called Robert
Hooke built this.
• It was the first microscope.
• He looked at many things down
his microscope and drew them
in great detail.
• For example this amazing flea!
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• Hooke also looked at some cork
under his microscope and saw
this structure.
• He thought the compartments
looked like the small cells that
monks lived in.
• Therefore he called them cells
and that is where the term
came from.
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• After plenty more
research it was finally
realised that cells were
the basic unit of life.
• Schleiden and Schwann
coined the cell theory in
1839 which stated that
all living organisms are
made of one or more
cells and the cell is the
most basic unit of life.
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• Microscopes are now much
more advanced and a huge
amount has been discovered
about how cells work.
• There are two types of
microscope that you should
know about.
• They have various pros and
cons that we will review.
Light
Microscope
Electron
Microscope

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• The microscopes can magnify the image by this many
times.
Light Microscope Electron Microscope
X1500 X500,000

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• However, it is also about how
much detail they can show.
• This is measured by the
resolving power or resolution
of the microscope.
• The resolution tells you the
limit that two objects are seen
as two objects, any closer and
it would appear as one.
• This is a measure of detail. Low resolution
High resolution

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• The resolving power of these microscopes:
Light Microscope Electron Microscope
200nm 0.5nm
1nm = 0.000,001mm

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1. Light enters here, either by a built in lamp or
a light shone on the mirror.
2. The light is reflected up through a condenser which
focusses the beam of light and then through specimen which
is mounted on a slide and placed on the stage.
3. It then passes up through one of the objective lenses.
There are usually three different objective lenses to choose
from.
4. It then passes through the eyepiece lens where the image
is magnified again before entering the eye.
Light Microscope

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• To work out the total magnification you just multiply the
objective lens with the eyepiece lens.
• In order to prepare a slide for viewing on a light
microscope you need to make sure the sample is thin
enough for light to pass through.
• Most biological matter, especially when cut in a thin slice,
is transparent so usually a stain is added to highlight
certain structures.
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Eyepiece lens magnification x Objective lens magnification = Total magnification
x10 x x40 = x400

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• Here are some common stains.
Haematoxylin and Eosin Stain Methylene Blue Iodine
Stains nuclei purple and
cytoplasm pink
Stains nuclei blue in animal
cells
Stains starch granules in
plant cells blue/black

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• Good
– Cheap, accessible and portable
– Can look at live cells with little
preparation
– For example blood samples and
sperm
• Bad
– Limited in terms of magnification
(X1500) and resolution (200nm).

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• The electron microscope works in a similar principle to
the light microscope, but a beam of electrons is used
instead of a beam of light.
• The electron beam has a much smaller wavelength so
can be magnified much more and has a higher
resolution.
• The beam is focused by magnets not lenses.
• There are two types the transmission electron
microscope (TEM) and the scanning electron microscope
(SEM).
Electron Microscope

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