Module 4: Section 1 - Disease and the Immune System

Question 1

Define direct transmission and give several examples

Answer 1

Direct transmission is when a disease is transmitted directly from one organism to another. Examples include droplet infection (coughing or sneezing tiny droplets of mucus or saliva directly onto someone, sexy times or touching an infected organism

EXAMPLE: HIV can be transmitted through the sexytimes and athletes foot can be transmitted via touch

Question 2

Define indirect transmission and give several examples

Answer 2

Indirect transmission is when a disease is transmitted from one organism to another through an intermediate. Intermediates include air, water, food or a vector

Question 3

What three factors affect disease transmission?

Answer 3

Living conditions, climate and social factors

Question 4

How do living conditions affect disease transmission and give an example?

Answer 4

Overcrowded living conditions increase the transmission of many communicable diseases.

E.g. TB is spread directly via droplet infection. It’s also spread indirectly because the bacteria can remain in the air for long periods of time and infect new people. The risk of TB infection is increased when lots of people live crowded together in a small space.

Question 5

How does climate affect disease transmission and give an example?

Answer 5

Potato/tomato late blight is especially common during wet summers because the spores need water to spread.

Malaria is most common in tropical countries, which are humid and hot. This is because these are the ideal conditions for mosquitoes (the malaria vectors) to breed/

Question 6

How can social factors increase the transmission of communicable diseases and give an example?

Answer 6

The risk of HIV infection is high in places where there’s limited access to:

• good healthcare - people are less likely to be diagnosed and treated for HIV, and the most effective anti-HIV drugs are less likely to be available, so the virus is more likely to be passed on to others
• good health education - to inform people about how HIV is transmitted and how it can be avoided e.g. condoms

Question 7

How does skin act as a primary, non-specific immune defense?

Answer 7

Skin - this acts as a physical barrier, blocking pathogens from entering the body. It also acts as a chemical barrier by producing chemicals that are antimicrobial and can lower pH, inhibiting the growth of pathogens.

Question 8

How do mucous membranes act as a primary, non-specific immune defense?

Answer 8

Mucous membranes - these protect body openings that are exposed to the environment. Some membranes secrete mucus - a sticky substance that traps pathogens and contains antimicrobial enzymes.

Question 9

How does blood clotting act as a primary, non-specific immune defense?

Answer 9

Blood clotting - a blood clot is a mesh of protein (fibrin) fibres. Blood clots plug wounds to prevent pathogen entry and blood loss. They’re formed by a series of chemical reactions that take place when platelets (fragments of cells in the blood) are exposed to damaged blood vessels.

Question 10

How does inflammation act as a primary, non-specific immune defense?

Answer 10

Inflammation - the signs of inflammation include swelling, pain, heat and redness. It can be triggered by tissue damage - the damaged tissue releases molecules, which increase the permeability of the blood vessels, so they start to leak fluid into the surrounding area. This causes swelling and helps to isolate any pathogens that may have entered the damaged tissue. The molecules also cause vasodilation, which increases blood flow to the affected area. This makes the area hot and brings white blood cells to the area to fight off any pathogens that may be present.

Question 11

How does wound repair act as a primary, non-specific immune defence?

Answer 11

Wound repair - the skin is able to repair itself in the event of injury and re-form a barrier against pathogen entry. The surface is repaired by the outer layer of skin cells dividing and migrating to the edges of the wound. The tissue below the wound then contracts to bring the edges of the wound closer together. It is repaired using collagen fibres - too many collagen fibres and you’ll end up with a scar.

Question 12

What three physical defences to plants have against pathogens and why are these defences effective?

Answer 12

1) most plant leaves and stems have a waxy cuticle, which provides a physical barrier against pathogen entry. It may also stop water collecting on the leaf, which could reduce the risk of infection by pathogens that are transferred between plants in water.
2) plant cells themselves are surrounded by cell walls. These form a physical barrier against pathogens that make it past the waxy cuticle.
3) plants produce a polysaccharide called callose. Callose gets deposited between plant cell walls and plasma membranes during times of stress, e.g. pathogen invasion. Callose deposition may make it harder for pathogens to enter cells. Callose deposition at the plasmodesmata (small channels in the cell walls) may limit the spread of viruses between cells.

Question 13

Plants don’t just rely on physical defenses. They also produce antimicrobial chemicals which kill pathogens or inhibit their growth. Give two examples.

Answer 13

Some plants produce chemicals called saponins. These are thought to destroy the cell membranes of fungi and other pathogens.

Plants also produce chemicals called phytoalexins, which inhibit the growth of fungi and other pathogens.

Question 14

Other chemicals secreted by plants are toxic to insects - what does this mean?

Answer 14

Other chemicals secreted by plants are toxic to insects - this reduces the amount of insect-feeding on plants and therefore reduces the risk of infection by plant viruses carried by insect vectors.

Question 15

Foreign antigens trigger an immune response. Summarise briefly the three steps involved.

Answer 15

1) antigens are molecules (usually proteins or polysaccharides) found on the surface of cells
2) when a pathogen (like a bacterium) invades the body, the antigens on its cell surface are identified as foreign, which activates cells in the immune system
3) the immune response involves specific and non-specific stages. The non-specific response happens in the same way for all microorganisms - whatever foreign antigens they have. The specific response is antigen-specific - it is aimed at specific pathogens. It involves white blood cells called T and B lymphocytes.

Question 16

What are the four main stages in the immune response?

Answer 16

1) phagocytes engulf pathogens
2) phagocytes activate T lymphocytes
3) T lymphocytes activate B lymphocytes, which divide into plasma cells
4) plasma cells make more antibodies to a specific antigen

Question 17

A phagocyte is a type of white blood cell that carries out phagocytosis. They’re found in the blood and in tissues and carry out a non-specific immune response. Give the 5 steps in how they work.

Answer 17

1) a phagocytes recognises the antigens on a pathogen.
2) the cytoplasm of the phagocyte moves round the pathogen, engulfing it. This may be made easier by the presence of opsonins - molecules in the blood that attach to foreign antigens to aid phagocytosis
3) the pathogen is now contained in a phagosome (a type of vesicle) in the cytoplasm of the phagocyte
4) a lysosome fuses with the phagosome. The enzymes break down the pathogen
5) the phagocyte then presents the pathogen’s antigens, It sticks the antigens on its surface to activate other immune system cells. When a phagocyte does this it is acting as an antigen-presenting cell (APC).

Question 18

How do opsonins work?

Answer 18

Opsonins work in different ways. Some hide the negative charges on the membrane of the pathogen, making it easier for the negatively-charged phagocyte to get closer to the pathogen.

Question 19

What are neutrophils and what do they do?

Answer 19

Neutrophils are a type of phagocyte. They’re the first white blood cells to respond to a pathogen inside the body. Neutrophils move towards a wound in response to signals from cytokines (proteins that act as messenger molecules). The cytokines are released by cells at the site of the wound.

Question 20

The second stage in the immune response is: phagocytes activate T lymphocytes. Give the seven steps in which this happens.

Answer 20

1) A T lymphocyte is another type of white blood cell
2) their surface is covered with receptors
3) the receptors bind to antigens presented by APCs
4) each T lymphocyte has a different receptor on its surface
5) when the receptor on the surface of a T lymphocyte meets a complementary antigen, it binds to it - so each T lymphocyte will bind to a different antigen
6) this activates the T lymphocyte - the process is called clonal selection
7) the T lymphocyte then undergoes clonal expansion - it divides to produce clones of itself. Different types of T lymphocytes carry out different functions.

Question 21

What three different types of activated T lymphocyte cells are there and what do they do?

Answer 21

1) T helper cells - these release substances to activate B lymphocytes and T killer cells
2) T killer cells - these attach to and kill cells that are infected with a virus
3) T regulatory cells - these suppress the immune response from other white blood cells. This helps to stop immune system cells from mistakenly attacking the host’s body cells

Question 22

The third stage in the immune response is: T lymphocytes activate B lymphocytes, which divide into plasma cells. What seven steps occur in this stage?

Answer 22

1) B lymphocytes are another type of white blood cell
2) they’re covered with proteins called antibodies
3) antibodies bind to antigens to form an antigen-antibody complex
4) each B lymphocyte has a different shaped antibody on its surface
5) when the antibody on the surface of a B lymphocyte meets a complementary shaped antigen, it binds to it - so each B lymphocyte will bind to a different antigen
6) this, together with substances released from T helper cells, activates the B lymphocyte. This process is another example of clonal selection
7) the activated B lymphocyte divides by mitosis, into plasma cells and memory cells. This is another example of clonal expansion

Question 23

Cell signalling is how cells communicate. Briefly tell me how this works.

Answer 23

A cell may release a substance that binds to the receptors on another cell - this causes a response of some kind in the other cell.

Question 24

Why is cell signalling important in the immune response and give an example of how it is used?

Answer 24

Cell signalling is really important in the immune response because it helps to activate all the different types of white blood cells that are needed.

For example, T helper cells release interleukins (a type of cytokine) that bind to receptors on B lymphocytes. This activates the B lymphocytes - the T helper cells are signalling to the B lymphocytes that there’s a pathogen in the body.

Question 25

The fourth and final step in the immune response is: plasma cells make more antibodies to a specific antigen. What are the three steps in this stage?

Answer 25

1) plasma cells are clones of the B lymphocyte
2) they secrete loads of the antibody, specific to the antigen, into the blood
3) these antibodies will bind to the antigens on the surface of the pathogen to form lots of antigen-antibody complexes

Question 26

Talk me through the structure of antibodies. See pg 99 for a diagram also.

Answer 26

• the variable regions of the antibody form the antigen binding sites
• the shape of the variable region is complementary to a particular antigen. The variable regions differ between antibodies
• the hinge region allows flexibility when the antibody binds to the antigen
• the constant regions allow binding to receptors on immune system cells, e.g. phagocytes. The constant region is the same (i.e. it has the same sequence of amino acids) in all antibodies
• disulphide bridges hold the polypeptide chains of the protein together

Question 27

How does agglutinating pathogens help to clear an infection?

Answer 27

agglutinating pathogens - each antibody has two binding sites, so an antibody can bind to two pathogens at the same time - the pathogens become clumped together. Phagocytes then bind to the antibodies and phagocytose a lot of pathogens all at once. Antibodies that behave in this way are known agglutinins.

Question 28

How does neutralising toxins help to clear an infection?

Answer 28

Neutralising toxins - like antigens, toxins have different shapes. Antibodies called anti-toxins can bind to the toxins produced by pathogens. This prevents the toxins from affecting human cells, so the toxins are neutralised. The toxin-antibody complexes are also phagocytosed.

Question 29

How does preventing pathogens from binding to human cells help to clear an infection?

Answer 29

When antibodies bind to the antigens on pathogens, they may block the cell surface receptors that the pathogens need to bind to the host cells. This means the pathogen can’t attach to or infect the host cells.

Question 30

When a pathogen enters the body for the first time, the antigens on its surface activate the immune system. What is this called?

Answer 30

The primary response.

Question 31

Why is the primary response slow?

Answer 31

The primary response is slow because there aren’t many B lymphocytes that can make the antibody needed to bind to it.

Question 32

Talk me through the four steps of primary response which leads to a person’s immunity to that particular pathogen.

Answer 32

1) Eventually the body will produce enough of the right antibody to overcome the infection. Meanwhile the infected person will show symptoms of the disease.
2) After being exposed to an antigen, both T and B lymphocytes produce memory cells. These memory cells remain in the body for a long time.
3) Memory T lymphocytes remember the specific antigen and will recognise it a second time around. Memory B lymphocytes record the specific antibodies needed to bind to the antigen.
4) The person is now immune - their immune system has the ability to respond quickly to a second infection.

Question 33

If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response. What is this response and explain how it works?

Answer 33

The secondary response - clonal selection happens faster. Memory B lymphocytes are activated and divide into plasma cells that produce the right antibody to the antigen. Memory T lymphocytes are activated and divide into the correct type of T lymphocytes to kill the cell carrying the antigen.

The secondary response often gets rid of the pathogen before you begin to show any symptoms.

Question 34

What is a blood smear?

Answer 34

A blood smear is a sample of blood smeared over a microscope slide.

Question 35

What are you likely to see when looking at a blood smear?

Answer 35

Red blood cells, white blood ells and platelets. Some types of white blood cells have granules in their cytoplasm (so they look grainy) and other types don’t.

Question 36

What is active immunity?

Answer 36

This is the type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen.

Question 37

Define the two different types of active immunity.

Answer 37

Natural - this is when you become immune after catching a disease. e.g. if you have measles as a child, you shouldn’t be able to catch it again later on in life

Artificial - this is when you become immune after you’ve been given a vaccination containing a harmless dose of antigen

Question 38

What is passive immunity?

Answer 38

This is the type of immunity you get from being given antibodies made by a different organism - your immune system doesn’t produce any antibodies of its own

Question 39

Define the two types of passive immunity.

Answer 39

Natural - this is when a baby becomes immune due to the antibodies it receives from its mother, through the placenta and breast milk

Artificial - this is when you become immune after being injected with antibodies from someone else. e.g. if you contract tetanus you can be injected with antibodies against the tetanus toxin, collected from blood donations

Question 40

What are the four main differences between active and passive immunity?

Answer 40

Active immunity:

• requires exposure to antigen
• it takes a while for protection to develop
• protection is long-term
• memory cells are produced

Passive immunity:

• no exposure to antigen
• protection is immediate
• protection is short-term
• memory cells aren’t produced

Question 41

Give two examples and the causes of autoimmune diseases.

Answer 41

• lupus - caused by the immune system attacking cells in the connective tissues. This damages the tissues and causes painful inflammation. Lupus can affect the skin and joints as well as organs.
• rheumatoid arthritis - caused by the immune system attacking cells in the joints. Again this causes pain and inflammation.

Question 42

What is an abnormal immune response and what does this result in?

Answer 42

Sometimes, an organism’s immune system isn’t able to recognise self-antigens

When this happens, the immune system treats the self-antigens as foreign antigens and launches an immune response against the organism’s own tissues

A disease resulting from this abnormal immune response is known as an autoimmune disease. Autoimmune diseases are usually chronic. They can often be treated, but not cured.

Question 43

Why is vaccination not the same as immunisation?

Answer 43

Vaccination is not the same as immunisation. Vaccination is the administration of antigens (in a vaccine) into the body. Immunisation is the process by which you develop immunity. Vaccination causes immunisation.

Question 44

What is herd immunity?

Answer 44

If most people in a community are vaccinated, the disease becomes extremely rare. This means that even people who haven’t been vaccinated are unlikely to get the disease as there is no one to catch it from. This is known as herd immunity -it helps to prevent epidemics.

Question 45

How does vaccination mean you become immune without getting any symptoms?

Answer 45

Vaccines contain antigens that cause your body to produce memory cells against a particular pathogen, without the pathogen causing disease. This means you become immune without getting any symptoms.

Question 46

Vaccines and vaccination programmes change - explain why with the example of the influenza vaccine.

Answer 46

1) the flu vaccine changes every year. That’s because the antigens on the surface of the influenza virus change regularly, forming new strains of the virus.
2) Memory cells produced from vaccination with one strain of the flu will not recognise other strains with different antigens. The strains are immunologically distinct
3) Every year there are different strains of the flu virus circulating in the population, so a different vaccine has to be made
4) Laboratories collect samples of these different strains, and organisations such as the WHO and CDC test the effectiveness of different flu vaccines against them
5) New vaccines are developed and one is chosen every year that is the most effective against the recently circulating flu viruses

Question 47

Give two examples of antibiotic resistant bacteria

Answer 47

1) MRSA causes serious wound infections and is resistant to several antibiotics, including meticillin
2) Clostridium difficile infects the digestive system, usually causing problems in people who have already been treated with antibiotics. It is thought that the harmless bacteria that are normally present in the digestive system are killed by the antibiotics, which C. difficile is resistant to. This allows C.difficile to flourish. C.difficile produces a toxin, which causes severe diarrhoea and cramps

Question 48

What is synthetic biology and the applications of this?

Answer 48

Synthetic biology involves using technology to design and make things like artificial proteins, cells and even microorganisms.

It has applications in lots of different areas, including medicine. For example, scientists are looking at engineering bacteria to destroy cancer cells, while leaving healthy body cells intact

Question 49

What are personalised medicines and how do they work?

Answer 49

• your genes determine how your body responds to certain drugs. Different people respond to the same drug in different ways -which makes certain drugs more effective for some people than others. This is where personalised medicines come in.
• personalised medicines are medicines that are tailored to an individual’s DNA. The theory is that if doctors have your genetic information, they can use it to predict how you will respond to different drugs and only prescribe the ones that will be most effective for you.

Question 50

What do scientists hope from studying the relationship between someone’s genetic make-up and their responsiveness to drugs?

Answer 50

Scientists hope that by studying the relationship between someone’s genetic make up and their responsiveness to drugs, more effective drugs can be produced in the future.

Question 51

How do we protected possible sources of drugs and why do we do this?

Answer 51

Possible sources of drugs need to be protected by maintaining the biodiversity on Earth. If we don’t protect them, some species could die out before we get a chance to study them.

Even organisms that have already been studied could still prove to be useful sources of medicines as new techniques are developed for identifying, purifying and testing compounds.

Question 52

Give three examples of a drug that is manufactured using natural compounds found in plants

Answer 52

-penicillin is obtained from a fungus, some cancer drugs are made using soil bacteria, and daffodils are now grown to produce a drug used to treat Alzheimer’s disease