j

1. © Boardworks Ltd 20041 of 40
KS4 Biology
What is Blood?

2. © Boardworks Ltd 20042 of 40
Contents
What is Blood?
What is blood made of?
Plasma
White blood cells
Red blood cells
Platelets
Summary activities

3. © Boardworks Ltd 20043 of 40
Blood and the circulatory system
The circulatory system is
made up of the heart, blood
and blood vessels.
What exactly is blood and
what does it do?
Blood is the fluid that flows
in the circulatory system
and carries substances
around the body.

4. © Boardworks Ltd 20044 of 40
How much blood?
How many litres of blood
are there in the circulatory
system of an average adult?
5.5 litres5.5 litres

5. © Boardworks Ltd 20045 of 40
What is blood made of?
Blood is made up of a liquid
called plasma and blood cells
that float in this plasma.
If a test tube of blood is left
to stand for a while what
happens to it?
The blood cells sink to the
bottom of the test tube and
separate from the plasma
which is a clear yellow liquid.
The liquid in blood is yellow!
So why does blood look red?
blood cells
(45% of
volume)
plasma
(55% of
volume)

6. © Boardworks Ltd 20046 of 40
Different types of blood cells
Blood plasma carries three types of blood cells.
They have different shapes and carry out different functions.
red
blood cell
white
blood cell
platelet

7. © Boardworks Ltd 20047 of 40
What’s in a drop of blood?

8. © Boardworks Ltd 20048 of 40
Contents
What is Blood?
What is blood made of?
Plasma
White blood cells
Red blood cells
Platelets
Summary activities

9. © Boardworks Ltd 20049 of 40
Blood flows around the body
transporting substances from
one place to another.
Plasma is the blood fluid that
surrounds blood cells and
carries them along as it flows
through the blood vessels.
Plasma is mostly water and
contains other substances that
are dissolved in it.
What useful and waste
substances are dissolved in
and transported by plasma?
What does plasma do?

10. © Boardworks Ltd 200410 of 40
What is dissolved in plasma?
Plasma is mostly water with other
substances dissolved in it.
 Useful substances dissolved
in plasma are digested food.
This must be transported to
where it is needed in the body.
 Waste substances dissolved
in plasma are carbon dioxide
and urea.
These must be transported to
where they can be removed
from the body.

11. © Boardworks Ltd 200411 of 40
Plasma: transporting digested food
The digestive system breaks long insoluble molecules of
food into small soluble molecules that the body can use.
Where does soluble digested food enter the blood?
Soluble digested food diffuses from the small intestine
into the bloodstream and dissolves in the plasma.
The digested food is then carried to the body’s cells
and used in various chemical reactions.
digested food
in blood plasma

12. © Boardworks Ltd 200412 of 40
Carbon dioxide is produced by respiration in the body’s cells.
This waste product is poisonous to the body and so must
be removed as quickly as possible. How does this happen?
Plasma: transporting carbon dioxide
carbon dioxide
in blood plasma
Carbon dioxide diffuses from body cells into the blood
where it dissolves in plasma.
Carbon dioxide then carried from the cells to the lungs.
How is this waste product finally removed from the body?

13. © Boardworks Ltd 200413 of 40
Urea is another waste substance that is transported by the
blood. It is made in the liver.
Urea is toxic to the body and must be removed as quickly
as possible.
Plasma: transporting urea
urea
in blood plasma
Urea enters the blood in the liver and dissolves in plasma.
It is then carried from the liver to the kidneys.
The kidneys filter blood and remove urea from plasma.
This waste product is then removed from the body in urine.

14. © Boardworks Ltd 200414 of 40
Dissolved substances in plasma

15. © Boardworks Ltd 200415 of 40
What does plasma do?

16. © Boardworks Ltd 200416 of 40
Contents
What is Blood?
What is blood made of?
Plasma
White blood cells
Red blood cells
Platelets
Summary activities

17. © Boardworks Ltd 200417 of 40
Red blood cells are the most
common type of blood cell.
What do red blood cells do?
The job of red blood cells is to transport oxygen from the
lungs to the body’s cells, where is used in respiration.
The body contains millions and millions of red blood cells.
Why does it need so many?
oxygen

18. © Boardworks Ltd 200418 of 40
Features of a red blood cell
A red blood cell has several features that help it do its job:
Disc-shaped, with
a dent on each
side, creates a
large surface area
for gas exchange.
A large surface
area compared to
volume, so oxygen
is always close to
the surface.
It has no nucleus,
so there is more
space for
haemoglobin and
so more oxygen.
It contains
haemoglobin,
a special pigment
that combines
with oxygen.

19. © Boardworks Ltd 200419 of 40
Another important feature of a red blood cell is its size.
How does this help the release of oxygen?
The size of a red blood cell forces it to slow down as it
passes through a capillary. The surface of the red blood
cell is exposed to the surface of the capillary and so gas
exchange will definitely happen.
Another feature of red blood cell
The diameter of a red blood cell is slightly bigger
than the average diameter of a capillary.

20. © Boardworks Ltd 200420 of 40
Features of a red blood cell – activity

21. © Boardworks Ltd 200421 of 40
haemoglobinhaemoglobin
Red blood cells and haemoglobin
Haemoglobin is the special pigment in red blood cells.
At the lungs, oxygen diffuses into red blood cells and
combines with haemoglobin to form oxyhaemoglobin.
This is how red blood cells are able to bind to oxygen and
carry it in the blood.
Oxyhaemoglobin makes red blood cells appear bright red.
oxygenoxygen
++ oxyhaemoglobinoxyhaemoglobin

22. © Boardworks Ltd 200422 of 40
++
oxygenoxygen
haemoglobinhaemoglobin
Red blood cells and haemoglobin
Red blood cells loaded with oxyhaemoglobin carry oxygen
from the lungs to the body’s cells.
Here, oxyhaemoglobin changes back to haemoglobin and
oxygen is released.
Oxygen is then able to diffuse into the body’s cells.
Why do red blood cells appear a dull red colour when
oxygen is released?
oxyhaemoglobinoxyhaemoglobin

23. © Boardworks Ltd 200423 of 40
Journey of a red blood cell
Oxygen enters the body
when air is inhaled into
the lungs.
How does this oxygen
enter the blood?
Oxygen diffuses from
the alveoli on the
surface of the lungs
into the bloodstream.
The oxygen then
diffuses into the red
blood cells where it
meets haemoglobin.
(not to scale)
oxygen +
haemoglobin
oxygen +
haemoglobin

24. © Boardworks Ltd 200424 of 40
oxyhaemoglobinoxyhaemoglobin
Journey of a red blood cell
In the red blood cells
at the lungs, oxygen
combines with
haemoglobin to form
oxyhaemoglobin.
This oxygen-rich
blood travels from
the lungs, through the
circulatory system,
to body cells.
How does oxygen get
from red blood cells
into the body’s cells?
oxygen +
haemoglobin
oxygen +
haemoglobin
(not to scale)
oxyhaemoglobinoxyhaemoglobin

25. © Boardworks Ltd 200425 of 40
Journey of a red blood cell
When red blood cells
reach the body’s cells,
oxyhaemoglobin
changes back to
haemoglobin and
oxygen is released.
Oxygen then diffuses
from the red blood cells
across the lining of the
capillary and into the
body’s cells.
What happens next to
the red blood cells?
oxygen +
haemoglobin
oxygen +
haemoglobin
oxyhaemoglobinoxyhaemoglobin
(not to scale)
haemoglobinhaemoglobin
+ oxygen+ oxygen
oxyhaemoglobinoxyhaemoglobin

26. © Boardworks Ltd 200426 of 40
haemoglobinhaemoglobin
+ oxygen+ oxygen
Journey of a red blood cell
Red blood cells that
have released oxygen
to the body’s cells have
to get back to the lungs.
So this oxygen-poor
blood travels from the
body’s cells through the
circulatory system.
At the lungs, the red
blood cells can pick up
more oxygen and start
another journey around
the body.
oxygen +
haemoglobin
oxygen +
haemoglobin
oxyhaemoglobinoxyhaemoglobin
(not to scale)
oxyhaemoglobinoxyhaemoglobin

27. © Boardworks Ltd 200427 of 40
Red blood cells in an alvelous

28. © Boardworks Ltd 200428 of 40
Red blood cells in a capillary bed

29. © Boardworks Ltd 200429 of 40
How do red blood cells carry oxygen?

30. © Boardworks Ltd 200430 of 40
Contents
What is Blood?
What is blood made of?
Plasma
White blood cells
Red blood cells
Platelets
Summary activities

31. © Boardworks Ltd 200431 of 40
What do white blood cells do?
White blood cells are the largest type of blood cell.
They have a large nucleus and can change their shape.
White blood cells protect the body from disease by
fighting invading microbes that can cause infection.
White blood cells can squeeze through the walls of
capillaries. How does this help them fight against
microbes?

32. © Boardworks Ltd 200432 of 40
Different types of white blood cells
Different types of white blood cells protect the body
in different ways:
Some white blood cells fight against infection by
surrounding invading microbes and then digesting them!
Other white blood cells produce antibodies or antitoxins
to fight against infection.

33. © Boardworks Ltd 200433 of 40
White blood cell count
unwell
white blood cell
number is high
healthy
white blood cell
count is low
Doctors can check the number of white blood
cells in a person’s blood to find out if they are
healthy or fighting off an infection.
Why is the white blood cell count higher when a person
is fighting off an infection?

34. © Boardworks Ltd 200434 of 40
Contents
What is Blood?
What is blood made of?
Plasma
White blood cells
Platelets
Red blood cells
Summary activities

35. © Boardworks Ltd 200435 of 40
Platelets are the third type of blood cell.
They are important for blood clotting.
What do platelets do?
Platelets are cell fragments that have broken off from
other larger cells.
They are much smaller than red and white blood cells
and do not have a nucleus.
platelet

36. © Boardworks Ltd 200436 of 40
Platelets and blood clotting
Platelets help to
make tiny fibres
that form a net at
the site of a cut.
11 The clot dries and
forms a scab which
protects the cut
while new skin grows.
33
Red blood cells
are trapped in
this net forming
a blood clot.
22
Why is it important
not to pick a scab?

37. © Boardworks Ltd 200437 of 40
Contents
What is Blood?
What is blood made of?
Plasma
White blood cells
Red blood cells
Platelets
Summary activities

38. © Boardworks Ltd 200438 of 40
What do blood cells do?

39. © Boardworks Ltd 200439 of 40
Which type of blood cell?

40. © Boardworks Ltd 200440 of 40
Multiple-choice quiz