1. Parts of the blood
Blood is the fluid circulating in the body that carries nutrients and oxygen, removes waste products and fights infection.
Red Blood Cells
Plasma
White Cells
Platelets
Photo information: Human blood cells, coloured scanning electron micrograph (SEM). Seen here are red blood cells (red), a lymphocyte (pink), a neutrophil (large cream cell), a macrophage (green) and platelets (small cream cells). Magnification: x3300 when printed at 10 centimetres wide.

2. Red blood cells
Red blood cells carry oxygen to the body’s organs and tissues.
The inside of the red blood cell is filled with the protein haemoglobin.
Questions you may like to ask about red blood cells:
Q. Look at the shape. Why is this pressed in disc a better shape than a flat disc?
A. It has a greater surface area, so can take up more oxygen.
Q. Look at the colour. What do you notice about the shades of red?
A. Red blood cells without oxygen are a dull red, but oxyhaemoglobin (red blood cells combined with oxygen) are bright red.
Photo information: Red blood cell. Coloured scanning electron micrograph (SEM) of a red blood cell. This disc-shaped cell, also known as an erythrocyte, transports oxygen from the lungs to the tissues during respiration. It contains large amounts of haemoglobin, a pigmented protein which binds oxygen. It is one of several types of blood cell, all of which develop from stem cells in the bone marrow. The formation of a red blood cell is known as Erythropoiesis and takes about five days. Magnification: 11,200 at 6x7cm size.

3. Plasma Blood cells float in a straw-coloured liquid called plasma
Plasma consist of water and many dissolved substances required in the body
A question you may like to ask about plasma:
Q. What substances do you think might be carried in the plasma? (Think about the things that your body must take in and get rid of)
A. Examples include: food, waste (urea) and hormones.

4. White blood cells
White blood cells attack invading microbes that cause disease
They do this in two ways:
1. One type of white blood cell produces chemicals called antibodies.
These antibodies lock on to proteins called antigens on the surface of the microbes.
2. Another type of white blood cell digests any microbes the antibodies lock on to.
Questions you may like to ask about white blood cells:
Q. Why do you think our neck glands swell up when we get a cold?
A. Millions of new white blood cells are being made in the glands to fight the cold virus.
Photo information: White blood cell. Coloured scanning electron micrograph (SEM) of a T-lymphocyte, a type of white blood cell. T-lymphocytes characteristically have long microvilli that project from the cell's surface. They are an important part of the body's immune system. They track down and destroy foreign bodies and infected cells. They also help to mediate the production of antibodies to invading organisms, such as bacteria and viruses. Tlymphocytes originate in the bone marrow, but mature in the thymus gland. Magnification: x9250 when printed 10cm high.
White blood cells attack invading microbes that cause disease.

5. Platelets Platelets are bits of cell broken off large cells They
help blood to clot
and stop bleeding at cuts.
Questions you may like to ask about platelets:
Q. What do you think happens if a wound is very large and the blood does not clot fast enough?
A. You lose too much blood and require a blood transfusion – that is the transfer of blood from one person to another.
Photo information: Platelets, responsible for the clotting action in blood, shown in an image created with a Scanning Electron Microscope (SEM).

6. Blood transfusions save lives everyday
One-off to replace a sudden loss of blood, e.g. following a serious accident, during surgery or childbirth, etc.
Ongoing to treat blood diseases like sickle cell anaemia or thalassaemia, or to treat cancer patients who survive their treatment.
Often transfusions are just of the part of the blood that the patient needs, e.g. red blood cells for sickle cell sufferers, whose own red cells are defective.
Medical breakthroughs like organ transplants increase the demand for donated blood.
Q: What is a blood transfusion?
A: Receiving donated blood, either whole blood or, more usually, just the parts of blood that you need.
Q: Why might you need a transfusion?
A: To replace lost blood, or regularly to treat a serious blood disease.

7. Donating blood What’s so special about turning 17?
At 17, if you are fit and healthy, you can donate blood.
This is a ‘unit’ of blood, about 450ml.
Donate this much and you can help save lives.
Donated blood gets separated, and its four component parts can be used to help more than one patient in need.
So, even a single donation can help several people.
Imagine how many people a regular donor can help…
But not everyone can donate to everyone…
Questions you may like to ask about blood donation:
Q. How do you think the blood is separated so that its component parts can help more than one person?
It gets put in a machine called a centrifuge and spun around a lot until the blood separates.
NOTE: Students may have met the use of a centrifuge when separating solutions in Year 8 (Unit 8F – Compounds and mixtures)
Q: Why is it important to give blood regularly, instead of just once?
Lots of donated blood is needed to supply enough of all the different blood parts and groups to meet everyday demand and to keep some in reserve for emergencies. Also, stored blood components don’t keep forever, so fresh supplies are needed to keep stocks up.
Q: How long does it take for your body to replace a unit of donated blood?
A: Your body is replacing worn out blood cells all the time, so you completely replace the blood you give. It takes a few hours to replace the fluid, 4 weeks to replace the red blood cells and 8 weeks to replace the iron.

8. Blood groups There are four blood groups – A, B, AB and O
Blood groups are classed as ‘positive’ with the presence of a particular antigen, ‘negative’ if it’s not there
Your parents’ blood groups affect what group you belong to
O is the only blood group that everyone can receive whatever group they belong to
Some blood groups are more common among some ethnic communities
Some ethnic communities are more likely to develop particular medical conditions that require blood donations
Questions you may like to ask:
Q. Does anyone know which blood group they are?
Q: Is blood group an inherited characteristic, or environmental?
A: Inherited.
An important point to mention:
Some blood groups are more common than others. A frequent misconception is that it’s only important to donate blood if you belong to a rare blood group. The demand for common blood groups is higher, so more is needed than rare groups. Also, the most common blood types vary between different ethnic groups, so it is important to get donations from people from a representative mix of ethnic backgrounds.

9. Blood groups in detail
Blood group
Group A:
Group B:
Group AB:
Group O:
Antigens
You have certain proteins (called antigens) on the surface of your red blood cells:
Has A
antigens B
A and B
Has neither A nor B
Antibodies
Your blood plasma contains certain antibodies which would attack red blood cell antigens that you do not have:
Against B antigens – Anti-B
Against A antigens – Anti-A
Against no antigens
Against A and B antigens – Anti-A, B
Can donate to:
Only those with antibodies that will NOT react with the antigens in the donated blood.
e.g. Group A donor can only donate to recipients without Anti-A
Can donate to Group A and Group AB
Can donate to Group B and Group AB
Can donate to Group AB
Can donate to all groups
Can receive from:
Only those whose antigens will NOT react with its own antibodies.
e.g. Group A recipient can receive from anyone without B antigens.
Can receive from Group A and Group O
Can receive from Group B and Group O
Can receive from all groups
Can only receive from Group O
NB: Check your exam specification for how much detail is appropriate here. Many do not require knowledge of antibodies and antigens, only the general principle.
Additional information:
What happens if a recipient receives the wrong blood type:
If a recipient’s plasma contains antibodies that correspond to a donor’s antigens, then the donor’s red blood cells clot together, blocking blood vessels and stopping supplies of oxygen and other substances from reaching the cells in the recipient’s body. This must be avoided.