IGCSE Edexcel Biology: blood

What is the composition of blood?

Plasma, red blood cells, white blood cells, platelets

Over 50% of volume of the blood is made up of plasma. Majority of the other half is made up of red blood cells. Remaining fraction consists of white blood cells and platelets.

What is the plasma?

Clear-straw coloured liquid (mostly water) in which blood cells, dissolved nutrients (e.g amino acids), hormones, CO2 and urea are suspended within.

What substances does plasma transport?

• Oxygen

• Carbon dioxide

• Digested food and mineral ions (e.g glucose, amino acids)

• Urea

• Hormones

• (Heat energy) normally not in mark scheme

Oxygen, transported in plasma

From lungs to all cells in body

Carbon dioxide, transported in plasma

Carbon dioxide - the waste product of respiration.

Dissolved in the plasma and transported from respiring cells to the lungs

Urea, transported in plasma

Urea - the waste substance produced in the breakdown of proteins by the liver.

Urea is dissolved in the plasma and transported from the liver to the kidneys

Hormones, transported in plasma

Hormones - chemical messengers released into the blood from the glands and delivered to target tissues/organs of the body

Heat energy, transported in plasma

Heat energy — created in respiration (an exothermic reaction), heat energy is transferred to cooler parts of the body or to the skin where heat can be lost

What is a red blood cell + its function? What are the adaptations of red blood cells?

Specialised blood cell that carry oxygen to respiring cells for aerobic respiration.

- Full of haemoglobin, a protein that binds to oxygen to form oxyhemoglobin.
- Have a biconcave disc shape to give a large surface area to volume ratio maximises diffusion of oxygen.
- Don't have a nucleus to free up space for more haemoglobin so more oxygen is carried.

Not in MS - Very small and flexible so they can pass through thin capillaries

What is a white blood cell? What are the two main types and 2 main ways they protect body against pathogens?

Specialised blood cell which is involved in the immune system of the body, that protects it from invading pathogens (via the production or antibodies and antitoxins).

Phagocytes and lymphocytes. Phagocytosis and antibodies

What do lymphocytes do?

- Produce antibodies that match certain antigens.
- When the antibodies stick to the microorganism it causes them to get stuck together in a lump.
- This makes it easier phagocytes to find them.
- Lymphocytes also clones itself, which all will produce the specific antibody required.

What are antibodies? In what ways can antibodies destroy pathogens?

Proteins with a shape that is specific to the antigens on the surface of the pathogen.

• Causing bacteria to stick together, so that pathogens can ingest them more easily

• Acting as a ‘label’ on the pathogen, so that it is more easily recognised by a phagocyte

• Causing bacterial cells to burst open

• Neutralising toxins produced by pathogens

What do phagocytes do? What is this process called? Describe what is happening at each state of the process where these white blood cells destroy pathogens (4 stages)

- Detect foreign bodies and engulf and destroy them.
- Phagocytosis

- Phagocytes engulfs pathogen/bacteria/etc
- They release digestive enzymes to digest it/vesicle fuses with bacteria/pathogen/etc.
- Bacteria inside vesicle.
- Products of digestion expelled from cell.

How can phagocytes detect foreign bodies?

- They have a sensitive cell surface membrane that can detect chemicals produced by pathogenic cells.

What type of immune response give the phagocytes and the lymphocytes? Why?

Phagocytes = non-specific immune response because they will engulf all types of pathogens they encounter.

Lymphocytes = specific immune response as the antibodies produced will only fit one type of antigen on a pathogen.

What causes symptoms in a patient?

A release of toxins (in the case of bacteria) and infection of body cells.

Start of triple: What is immunity?

When an organism has high levels of antibodies by producing them at a faster rate and in higher quantities.

This means the organism won't suffer from the disease or its symptoms.

REMEMBER: when pathogen enters the blood stream it multiplies (ns de qué me va a servir esta info)

What are vaccines used for?

Induce immunity to infectious diseases

Explain how vaccination can give a person immunity to a disease (5)

• Dead or weakened pathogen/bacteria/virus is injected

• Lymphocytes make antibodies specific to the antigen

• Antibodies stick to antigens on the pathogen (and phagocytes engulf and digest them)

• Some lymphocytes develop into memory cells. Secondary immune response produces higher number of antibodies and faster killing the pathogen before they have time to multiply to the point where they could cause disease.

What are methods that scientist use to ensure that vaccines contain harmless pathogens? How can vaccines be administered?

- Killing the pathogen
- Making the pathogen unable to grow or divide
- Using fragments of pathogens.

- Orally, nasally or via an injection

Continuation of triple: What are platelets?

Cell fragments involved in blood clotting (and forming scabs). Fragments of large cells made in the bone marrow.

How are platelets involved in blood clotting?

When the skin is broken (also broken blood vessel wall) (ie. there is a wound) exposure to air stimulates the platelets and damaged tissue to produce chemical. They arrive to stop the bleeding.

A series of reactions occur within the blood plasma:

• Platelets release chemicals that cause soluble fibrinogen proteins to convert into insoluble fibrin.

• This forms an insoluble mesh across the wound, trapping red blood cells and forming a clot.

• The clot eventually dries and develops into a scab.

End of triple: What does the process of blood clotting used for?

Prevents excessive blood loss and protects the wound from the entry of microorganisms until new skin has formed.