Download Blood cells - AIS IGCSE Science

KEY STAGE 4
BLOOD
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What is blood?
If blood is separated it no longer looks like the red liquid
that we recognise.
centrifuge
The blood sample separates into two parts.
The top half is a straw coloured liquid called Plasma (55%).
The bottom half is a dark collection of Blood cells (45%).
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As blood is 55% plasma and only 45%
cells, the cells are actually suspended
within the plasma, a little like people would
be suspended within a swimming pool.
blood cell
blood cell
blood cell
plasma
The plasma actually surrounds the cells and carries them
along as it flows through the blood vessels.
This is the first function of plasma.
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Blood flows around the body, transporting substances
from one place to another.
it usually picks a
substance up from an
exchange site
takes it to a place
where it is used
a reaction occurs
Reaction
a useful product and a
waste product is made
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The blood then transports one or both of these
substances to another place in the body.
blood vessel
cell
useful/waste product
The cycle then starts again.
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Blood has to rely on its plasma to actually carry some
of these useful/waste products.
For example, plasma carries CO2 from the cells to the
lungs.
Magnify
blood flowing along
a capillary
CO2
CO2
blood cell
plasma
CO2
CO2
CO2
blood cell
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The third and fourth roles are also centred around the
moving of a substance from one place to another.
3rd Role:
Plasma is responsible for carrying dissolved food.
Remember! Our digestive system breaks down the food
we eat to release the useful nutrients.
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Mouth
food is eaten
Sugars
Useful products of
digestion are
absorbed from the
digestive system and
enter the blood.
Amino Acids
Glycerol
Fatty Acids
Anus
waste is excreted
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The soluble food dissolves into the plasma and is
carried from the small intestine to the cells of the
body. Here they diffuse into the cells and are used
in various chemical reactions.
Glycerol
plasma
Sugars
Amino acids
Fatty acids
Body cell
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The final role of the plasma is to carry a waste product
from the liver to the kidneys.
The waste product is called Urea.
Urea is made in the liver by the breakdown of
amino acids.
As urea is toxic, it must be
removed from the body as
quickly as possible!
The blood now has to help
the body do this.
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This is where the plasma takes control.
It carries the urea from the liver to the filtering organs
(the kidneys). As the blood passes into the kidney, the
urea is removed from the plasma and passes down a
tube that takes it to the bladder.
kidney
blood
urea
This urea passes to the bladder where
it is stored before it is excreted.
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The urea will leave the body within the liquid urine.
In summary, this tells us that plasma has a principle
role in transporting substances around the body.
Substance Moving from
Going to
CO2
Cells
Lungs
Cells
All over
The Body
Dissolved
food
Small
intestine
Cells
Urea
Liver
Kidney
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We’ve come a long way from calling blood just a red liquid.
After all, all this is being carried in just the bloods plasma.
White
Blood Cell
Platelets
Sugar
Fatty
Acids
CO2
Red
Blood
Cell
CO2
Urea
Amino
Acids
Urea
Carbon Dioxide
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Blood cells
There are 3 types of blood cell within human blood.
They have different shapes and carry out different functions.
Platelets
Red Blood
Cells
White Blood
Cells
(These are actually
fragments of cells so we
can’t really call them cells)
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Red blood cells
Of all the cells these are the most numerous.
In fact, every cubic centimetre of blood contains…
1 cm
1 cm
1 cm
5 000,000,000 cells
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Therefore, it is not hard to realise that each red
blood cell is extremely small.
In fact, each one is only on average 7 micrometers in
diameter (one micrometer is a millionth of a metre).
This is a basic diagram of a red blood cell.
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Actually, although the red blood cell is a “cell”,
it does not contain one of the 3 parts of a
“normal” cell.
Red blood cells have no nucleus.
This may seem odd but, there is a reason for it.
Red blood cells also contain a unique substance
called Haemoglobin.
This is a special iron based pigment whose
presence is essential if the red blood cell is to
perform its job.
And by the way, its job couldn’t be more important!
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Red blood cells carry OXYGEN (O2).
Let’s look at how it performs this job.
The story begins in the lungs because this is where the
oxygen gas enters the bloodstream.
Remember, during the process of breathing, oxygen gas
enters the body and is exchanged for carbon dioxide gas.
The oxygen gas will be needed for the process of respiration.
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O2
oxygen is inhaled
O2
O2
It passes through the
breathing system and
reaches an alveolus.
O2
O2 O2
O2
alveolus
The oxygen gas diffuses
across the lining of the
alveolus and the capillary.
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Here is a close up showing the diffusion of oxygen gas.
As the oxygen gas diffuses across the lining of the
alveolus, it dissolves in the moist layer.
This speeds up the diffusion process.
O2
moist layer
O2
lining of alveolus
lining of capillary
red blood cell
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If we now concentrate on one red blood cell, we can
see how important the haemoglobin molecule is to the
process of transporting oxygen.
O2
each red blood cell
contains the pigment...
The oxygen molecule diffuses
into the red blood cell.
Haemoglobin + O2
Oxyhaemoglobin
These two molecules bind together to
produce this new substance.
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Oxygen + Haemoglobin
Oxyhaemoglobin
It is important to remember that this reaction is
happening in red blood cells at the alveolus.
This is how the red blood cells are able to bind hold of
the oxygen and carry it within the blood.
Oxyhaemoglobin
Oxyhaemoglobin
Oxyhaemoglobin
Each red blood cell is now Oxyhaemoglobin
loaded with oxygen molecules.
Oxyhaemoglobin
Oxyhaemoglobin
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Once these red blood cells reach the cells of
the body, they are travelling through tiny
capillaries similar to those found in the alveolus.
capillary
cells
It is here that they offload their oxygen.
In order for this to happen, the Oxyhaemoglobin
molecule must be broken down.
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ENERGY
In the cell, the oxygen is used
in the process of respiration
which produces….
It diffuses across the cell
membrane and the lining
of the capillary and into
the cell.
The Oxyhaemoglobin
breaks down to release
the oxygen molecule.
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Questions
Why are red blood cells shaped like this?
Well, they are perfectly suited to do their job.
They are specialised in the following ways -
1 There are vast numbers of them.
The more cells there are, the more O2 can be carried
and delivered to the cells.
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2 They have no nucleus.
This means they have more room for haemoglobin
molecules and therefore each red blood cell can carry
more oxygen gas.
3 They have a large surface area compared to their volume.
large surface area
small volume
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Through having a small volume compared to its
surface area, the red blood cell is able to keep the
oxygen close to its surface.
This means it can quickly release its oxygen by reducing
the time it takes for the gas to diffuse out of the cell.
The distance for the gas to move
is much smaller in a cell shaped
like this.
O2
alternative cell
design
O2
The overall effect of this means that the blood can
cope with the oxygen demands of the body.
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4 The diameter of red blood cells is slightly larger
than the average diameter of a capillary.
red blood cell
capillary
This means that the red blood cell is forced to slow down as it
passes through the capillary.
This means the exchange of the gas will definitely happen.
It also means the surface of the red blood cell will be
exposed to the surface of the capillary.
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Let’s now consider the white blood cell.
The white blood cell is bigger than the red blood cell.
It has a much more varied shape and there are
different types of white blood cell within the blood.
White blood cells play a part in the defence system of the body.
They are designed to fight microbes such as bacteria and
viruses.
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There are far fewer white blood cells within the blood
compared with red blood cells.
When the body fights disease, more white blood cells
are produced. With some diseases, doctors can
establish how healthy someone is by testing their blood
to see how many white blood cells they have.
Disease
Test
Test
Person is
Normal
white blood cell
number is low
Person is
suffering
from
disease
white blood cell
number is higher
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Our final cell is the platelet.
As we mentioned, the platelet is actually a fragment
of a cell.
Therefore it does not have a nucleus.
They are also much smaller than both the white and
red blood cells.
Their role is to help to clot the blood when the body has a wound.
Blood
capillary
skin
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Activity
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Multiple choice questions
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Which of these is not a function of blood?
A To support the body.
B To fight disease.
C To carry gases around the body.
D To carry hormones to their site of action.
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What is the name of the pigment within red
blood cells?
A haemoglycin
B haemoglobin
C haemoglycerol
D haemoglucose
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Which of these descriptions best suits the
shape of a red blood cell?
A a doughnut
B a round flat plate
C a biconcave disc
D a disc shaped shell
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What is missing from a red blood cell?
A the nucleus
B the cytoplasm
C the cell membrane
D answers A and B
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What is the name of the straw-coloured liquid in
which blood cells are suspended?
A haem liquid
B cytoplasma
C blood fluid
D plasma
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What percentage of blood is made up of
plasma?
A 20%
B 40%
C 55%
D 65%
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Which of the these substances are carried by
blood plasma?
A oxygen, glucose, urea and amino acids
B amino acids, carbon dioxide, oxygen and fatty acids
C fatty acids, glucose, oxygen, glycerol
D urea, fatty acids, amino acids and carbon dioxide
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Blood plasma...
A defends the body against invading microbes.
B helps the blood to clot.
C transports urea from the liver to the kidneys.
D binds to oxygen.
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Red blood cells...
A need oxygen.
B attract carbon dioxide.
C carry oxygen.
D repel carbon dioxide.
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The white blood cells are larger than red blood
cells. Their job is to...
A make the blood clot.
B carry oxygen to the cells of the body.
C defend the body against invading microbes.
D carry carbon dioxide.
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