Chapter 12- Defences Against Pathogens/ Disease

Question 1

Physical plant defences against pathogens

Answer 1

Callose- plants produce callose when under pathogen invasion. This is deposited between plant cell wall and plasma membranes making it harder for pathogens to enter cells.

Waxy cuticle- provided a physical barrier against pathogens. It also stops water collecting on the leaf, which reduces spread of pathogens by water

Cell wall form a physical barrier against pathigens

Question 2

Plant chemical defences against pathogens

Answer 2

Insect repellents- eg pine resin

Insecticides - for example pyrethins. They acts as insect neurotoxins

Antibacterial compounds - for example phenols. These disrupts bacterial and fungal cell membranes.

Antifungal compounds -for example chitinases which are enzymes that break down chitin in fungal cell wall.

Question 3

Animal non specific defences against pathogens

Answer 3

1) the skin- physical barrier, blocking pathogens from entering the body. Also a chemical barrier as it produces chemicals that are anti microbial

2) mucous membranes protect body openings eg nostrils as it traps pathogens and contains anti microbial enzymes

3) blood clots plug wounds to prevent pathogen entry and blood loss. Form from chemical reactions that take place when platelets are exposed to damaged blood vessels.

4) inflammation- damaged tissues release molecules that leak fluid to the surrounding area. This causes swelling and isolates pathogens that have entered damaged tissue. These molecules also cause vasodilation. This makes the area hot and brings white blood cells to fight off pathogens.

5) wound repair- skin is able to repair itself in the event of injury and reform a barrier against pathogen entry. It is repaired using collagen fibres.

6) expulsive fibres - this includes coughing and sneezing. This happens when mucous membranes are irritated by things like dust. Sneezing attempts to expel foreign objects.

Question 4

What is an immune response

Answer 4

An immune response is the body’s reaction to a foreign antigen. The immune response involves specific and non specific stages.

Question 5

What are the four main stages of the immune response

Answer 5

1) phagocytosis
2) T lymphocyte activation
3) B lymphocyte activation
4) Antibody production

Question 6

What are opsonins

Answer 6

Molecules in the blood that attach to foreign antigens to aid phagocytosis

Question 7

What is the process of phagocytosis

Answer 7

1) a phagocyte recognises the antigens on a pathogen

2) the cytoplasm of the phagocyte moves around the pathogen engulfing it. This may be easier with the presence of opsonins

3) the pathogen is now contained in a phagosome in the cytoplasm of the phagocyte

4) a lysosome fuses with the phagosome. The enzymes break down the pathogen.

5) the phagocyte then sticks the pathogen’s antigens onto its own surface to activate other immune cells. Here it acts as an antigen-presenting cell. (APC)

Question 8

What are neutrophils

Answer 8

They are a type of phagocyte and the first white blood cells to respond to a pathogen inside the body. They move towards a wound in response to cytokines.

Question 9

What are cytokines

Answer 9

They are proteins that act as messenger molecules. They are released by cells at the site of the wound.

Question 10

How does T lymphocyte activation occur

Answer 10

1) Each T lymphocyte is covered in receptors and each lymphocyte is different to the next

2) when the receptor on the surface of the T lymphocyte meets a complementary antigen, it binds to it. (Receptors on APCs)

3) this process activates the T lymphocyte and is known as clonal selection.

4) this activated T lymphocyte undergoes clonal expansion (divided to produce clones of itself)

Question 11

different types of activated T lymphocyte and their functions

Answer 11

1) T helper cells- release interleukins to activate B lymphocytes and T killed cells

2) T killer cells- attach to and kill cells that are infected with a virus

3) T regulatory cells- suppress the immune response from other white blood cells. This prevents immune system cells mistakenly attacking the host’s body cells.

Some activated T lymphocytes become memory cells.

Question 12

What is the process of B lymphocyte activation

Answer 12

1) B lymphocytes are covered in antibodies. These antibodies bind to antigens to form an antigen- antibody complex

2) when an antibody on the surface of a B lymphocyte meets a complementary antigen, it binds to it.

3) with help from substances released by T helper cells, this activates the B lymphocyte. (Clonal selection).

4) the activated B lymphocyte the divides by mitosis into plasma cells and memory cells (clonal expansion)

Question 13

What happens in antibody production

Answer 13

Plasma cells are clones of B lymphocytes. These secrete loads of the antibody, specific to the antigen in the blood. They bind it form lots of antigen-antibody complexes. This is a signal for the immune system to attack and destroy the pathogen.

Question 14

How to identify cells in a blood smear

Answer 14

1)red blood cells will not be stained as they do not have a nucleus

2) white blood cells have a multi-lobed nucleus and the cytoplasm is grainy

3)monocytes have a kidney bean shaped nucleus

4) lymphocytes are smaller than neutrophils and nucleus takes up most of the cell.

Question 15

What is the primary immune response

Answer 15

When a pathogen enters the body for the first time, the antigens on the surface activate the immune system. This is a primary response. This response is slow because there aren’t many B lymphocytes that can make the antibody needed to bind to the antigen. Eventually the body will produce enough of the right antibody to overcome the infection

Question 16

What do Memory T/B lymphocytes do

Answer 16

1) Memory T lymphocytes remember the specific antigen and will recognise it a second time round

2) Memory B lymphocytes record the specific antibodies needed to bind to the antigen

Question 17

What happens in the secondary immune response

Answer 17

If the same pathogen enters the body again, the immune system produces a quicker, stronger immune response. Clonal selection happens faster. Memory B lymphocytes divide into plasma cells that produce the right antibody to the antigen. Memory T lymphocytes are activated and divide into the correct T lymphocytes to kill the cell carrying the antigen. Secondary response often gets rid of pathogen before symptoms occur.

Question 18

How to maintain immunity

Answer 18

Memory B and T lymphocytes have a limited lifespan. Once they have died, the person is susceptible to attack by the pathogen again. Immunity is maintained by continual exposure to the pathogen, so you continue to make more B and T lymphocytes.

Question 19

Comparison between primary and secondary reponse

Answer 19

1) in primary, pathogen enters for 1st time, in secondary, pathogen enters for 2nd time

2) primary response is slow, secondary response is fast

3) in primary response, B and T lymphocytes are activated, in secondary response, memory cells are activated.

4) in primary response, there are symptoms. In secondary response, there is usually no symptoms.

Question 20

What is an antibody’s structure

Answer 20

1) the variable regions of the antibody form the antigen binding sites. It is complementary to a particular antigen.

2) the hinge region allows flexibility when the antibody binds to the antigen.

3) the constant regions allow binding to receptors on immune system cells eg phagocytes. Constant region is the same in all antibodies, and disulphide bridges hold the polypeptide chains of the protein together.

Question 21

Describe the process of agglutinating pathogens

Answer 21

1) each antibody has two binding sites, so an antibody can bind to two pathogens at the same time, so the pathogens become clumped together.

2) phagocytes then bind to the antibodies and phagocytose a lot of pathogens all at once.

3) antibodies that behave in this way are called agglutinins.

Question 22

Describe the process of neutralising toxins

Answer 22

1) like antigens, toxins have different shapes. Antibodies called anti-toxins can bind to the toxins produced by the pathogens.

2) this prevents the toxins from affecting human cells, so the toxins are neutralised.

3) the toxin-antibody complexes are also phagocytosed.

Question 23

How do antibodies prevent the pathogen from binding to host cells

Answer 23

1) 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.

2) This means the pathogen can’t attach to or infect the host cells.

Question 24

What is active immunity

Answer 24

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

Natural- this is when you become immune after catching a disease
Artificial - this is when you become immune after you have been given a vaccination containing a harmless dose of antigen.

Question 25

What is passive immunity

Answer 25

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 if it’s own.

Natural- this is when a baby become immune due to antibodies it receive from its mother, through the placenta and in breast milk
Artificial- this is when you become immune after being injected with antibodies from someone else.

Question 26

Comparison between active and passive immunity

Answer 26

1) active immunity required exposure to the antigen, but passive immunity doesn’t
2) active immunity takes a while for protection to develop but in passive immunity, protection is immediate
3) in active immunity, protection is long term, in passive immunity, protection is short term
4) in active immunity, memory cells are produced. In passive immunity, memory cells are not produced.

Question 27

What is an autoimmune disease

Answer 27

This is when an organism’s immune system isn’t able to recognise self-antigens. Therefore, the immune system treats the self antigens as foreign antigens and launches an immune response against the organisms own tissues.
An example is lupus, where the immune system attacks cells in the connective tissue.

Question 28

How do vaccines work

Answer 28

Vaccines contain antigens that causes your body to produce memory cells against a particular pathogen, without the pathogen causing disease. This means you become immune without getting any symptoms. These antigens may be free or attached to a dead or attenuated pathogen. Vaccines may be taken orally or injected.

Question 29

Disadvantage of taking vaccine orally

Answer 29

A disadvantage of taking a vaccine orally are that it could be broken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed into the blood. Sometimes booster vaccines are given later on to make sure more memory cells are produced.

If most people in a community are vaccinated, the disease becomes extremely rare. This is called herd immunity. This helps to prevent epidemics.

Question 30

What are some routine vaccines

Answer 30

1) the MMR - protects against measles, mumps and rubella. It is usually given to children as an injection at around a year old, and again before they start school. It contains attenuated measles, mumps and rubella viruses.

2) the meningitis C vaccine- protects against the bacteria that causes meningitis C. It is first given as an injection ti babies at 3 months. Boosters are then given to 1 year olds and teenagers.

Question 31

Why do vaccine and vaccination programmes change

Answer 31

Some pathogens can change their surface antigens. This means that when you are infected, the memory cells produced following a vaccination will not recognise the different antigens so the immune system has to start from stratch and carry out a primary response against these new antigens. Therefore, vaccines may have to change regularly.
For example the influenza vaccine changes every year, due to the antigens changing and new strains of the virus forming.

Question 32

What are antibiotics

Answer 32

Antibiotics are chemicals that kill or inhibit the growth of bacteria. They’re used by humans to treat bacterial infections. They can target bacterial cells without damaging human body cells.

Question 33

History of antibiotics

Answer 33

Penicillin was the first antibiotic to be isolated (by Alexander Fleming in 1928). Antibiotic use became widespread from the mid twentieth century- partly due to the successful treatment of soldiers with penicillin in the Second World War.

For the past few decades, we’ve been able to deal with bacterial infections pretty easily using antibodies and as a result, death rate from infectious bacterial disease has fallen dramatically.

Question 34

Risks of using antibiotics

Answer 34

They can cause side effects and even severe allergic reactions in some people. However the biggest risk is antibiotic resistance.

Question 35

What is antibiotic resistance

Answer 35

There is genetic variation in a population of bacteria. Genetic mutations make some bacteria naturally resistant to an antibiotic. This allows the bacteria to survive in a host and live longer, so it reporiduces many more times. These leads to the allele for antibiotic resistance being passed onto lots of offspring. It’s an example of natural selection.

Question 36

Problems with antibiotic resistance

Answer 36

Antibiotic resistance means that people infected with these pathogens cannot easily get rid of them with antibiotics. This means we are less able to treat some potentially life threatening bacterial infections

Question 37

Examples of antibiotic resistant bacteria

Answer 37

1) MRSA causes serious wound infections and is resistant to several antibiotics, including meticillin.

2) Clostridium difficile infects the digestive system. C. difficile is resistant to the antibiotics used to kill bacteria in the digestive system. This allows C. difficile to reproduce and it produces a toxin, that causes severe diarrhoea, fever and cramps.

Question 38

How to prevent antibiotic resistance

Answer 38

1) doctors are encouraged to reduce their use if antibiotics for example not to prescribe them for minor infection or to prevent infections except for people with weak immune systems.

2) patients are advised to take all of the antibiotics they are prescribed to make sure the infection is fully cleared and all bacteria has been killed.

Question 39

Sources of medicines

Answer 39

1) many medicinal drugs are manufactured using natural compounds found in plants, animals or microorganisms

2) examples: penicillin is obtained from a fungus, some cancer drugs are made using soil bacteria, daffodils are grown to produce a drug to treat Alzheimer’s disease

3) only a small proportion of organisms have been investigated so far so it’s possible that plants or microorganisms exist that contain compounds to treat currently incurable diseases eg aids.

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

Question 40

What is personalised medicine

Answer 40

These are medicines that are tailored to an individual’s DNA. The theory is that if doctors know your genetic information, they can predict how you will respond to different drugs and prescribe the ones that will be most effective for you.

Question 41

What is synthetic biology

Answer 41

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 eg medicine. For example, scientists are looking at engineering bacteria to destroy cancer cells, while leaving healthy body cells in.tact