Defense Against Infectious Disease (6.3, 11.1)

Question 1

What is a pathogen?

Answer 1

A disease causing agent that disrupts the normal physiology of the infected organism. They can be cellular (eg. bacteria) or acellular (eg. viruses).

Question 2

How do bacteria reproduce?

Answer 2

Binary fission (asexual reproduction). The bacterium divides into two identical daughter cells. It occurs quickly, thus allowing for a rapid rate of reproduction.

Question 3

Give three diseases caused by bacteria

Answer 3

Meningitis (caused by droplet infection, affects the brain).
Tuberculosis (caused by droplet infection, affects the respiratory organs).
Salmonella (caused by ingesting contaminated food, affects the digestive system).

Question 4

How do viruses reproduce?

Answer 4

The virus attaches to the host cell with its tail and injects its genetic material into the cell. It then hijacks the host cell and uses it to produce more viruses.

Question 5

Give three viral diseases

Answer 5

Influenza (caused by droplet infection, affects the respiratory organs).
Smallpox (caused by droplet infection/contact, affects the skin/blood).
Ebola (caused by contact with body fluids, affects the immune system cells).

Question 6

Why are antibiotics ineffective against viruses?

Answer 6

Because viruses do not undergo metabolic reactions.

Question 7

How are infectious diseases spread?

Answer 7

• Direct contact (eg. sexual transmission)
• Insect bites
• Droplets
• Contaminated food/water

Question 8

How do pathogens enter the body?

Answer 8

• Natural openings
• Untreated wounds
• Insect/animal bites

Question 9

What are common symptoms of a disease?

Answer 9

Increased temperature (to kill the pathogen).
Inflammation (increased blood flow to infected area).
Swollen glands (white bloods cells fighting the pathogen in the glands).
Tiredness (energy is used to fight the pathogen).
Increased secretions/pus (to sweep pathogens out of the body).

Question 10

The first line of defence.

Answer 10

Surface barriers that prevent the pathogens entry to the body.

Question 11

Examples of the first line of defence.

Answer 11

The skin protects internal structures. It is waterproof and contains chemicals that are antimicrobial (sebum, earwax, sweat and tears).

Mucous membranes protect internal structures (externally accessible tubes such as the trachea). Mucus is an antiseptic sticky secretion that traps pathogens and dust. It contains lysozyme, an enzyme which is effective against bacteria. The cilia hairs sweep the mucus and trapped pathogens out of the respiratory system into the nose/mouth where physical actions such as coughing and sneezing remove the pathogens from the body entirely.

Question 12

What is the function of clotting?

Answer 12

To prevent blood loss and limit pathogenic access to the bloodstream.

Question 13

What are the components of blood clots?

Answer 13

Platelets and fibrin strands.

Question 14

Describe the process of clotting.

Answer 14

This process is collectively called the coagulation cascade. It is stimulated by the release of clotting factors from damaged cells or platelets.

Clotting factors triggers the production of thrombin which catalyses the production of fibrin. Fibrin forms a mesh of fibres across the wound and traps blood cells to form a insoluble, temporary clot. When exposed to air the clot dries to form a protective scab.

When the wound has healed the enzyme plasmin is activated to dissolve the clot.

Question 15

Haemophilia

Answer 15

A bleeding disorder where blood doesn’t clot normally. People with haemophilia have lower levels of clotting factors in their blood so the normal coagulation cascade is impaired and fibrin formation does not occur. This means a lasting blood clot does not form.

Question 16

The second line of defence.

Answer 16

The innate immune system (phagocytes). It is non-specific in its response (i.e. it does not differentiate between different types of pathogens and responds to an infection the same way every time).

Question 17

What are leucocytes?

Answer 17

A general term for white blood cells. There are two types: phagocytes and lymphocytes.

Question 18

How does the second line of defence work?

Answer 18

Damaged tissues release chemicals (eg. histamine) that dilate blood vessels and increase capillary permeability, causing inflammation. This draws white blood cells (phagocytes) to the site of infection. The pathogens are engulfed when cellular extensions surround the pathogen and fuse to form an internal vesicle. This vesicle is then fused to a lysosome and the pathogen is digested. Fragments of the pathogen (antigens) may be present on the surface of the phagocyte in order to stimulate the third line of defence.

Question 19

What are the effects of the release of histamine?

Answer 19

Inflammation. The widening of the blood vessels (dilation) and increased capillary permeability increase the blood flow to the area and thus the supply of defence cells. However, this causes inflammation of which the symptoms are redness, heat, swelling and pain.

Question 20

The third line of defence.

Answer 20

The adaptive immune system. It is specific in its response (i.e. it can differentiate between pathogens and target a response that is specific to the given pathogen. It can respond rapidly upon re-exposure to a specific pathogen, preventing symptoms from developing in a process called immunological memory.)

Question 21

Define antigens.

Answer 21

Substances that the body recognises as foreign that induce an immune response.

Question 22

Define antibodies.

Answer 22

Proteins produced by B lymphocytes and plasma cells that target a specific pathogen.

Question 23

Describe the leukocytes used in the third line of defence.

Answer 23

Lymphocytes defend the body by producing antibodies. They are found in the lymph nodes and the blood stream.

B lymphocytes: Found in the bone marrow.
They produce antibodies that recognise and target particular pathogen fragments (antigens).

T lymphocytes: Found in the thymus gland.
They release chemicals (cytokines) to activate specific B lymphocytes.

Cytotoxic T-cells (killer T cells) specifically destroy cells that are infected or cancerous.

Question 24

How are antibodies produced in the third line of defence?

Answer 24

After engulfing a pathogen some phagocytes will have antigen fragments on their surface. These cells (called dendritic cells) move to the lymph nodes and activate specific helper T lymphocytes. The helper T lymphocytes release cytokines to activate the B cell capable of producing antibodies specific to the antigen. The B cell will divide and differentiate to form plasma cells which produce high amounts of the specific antibody. The antibodies will target and destroy the specific antigen. Some of the B cells and helper T cells will develop into memory cells to provide long-lasting immunity.

Question 25

How do antibodies inactivate pathogens?

Answer 25

Antibodies attack antigens by binding to them. This neutralises the antigen as it changes its chemical composition.

Question 26

What is HIV?

Answer 26

HIV stands for the Human Immunodeficiency Virus. It infects helper T cells, thus disabling the body’s adaptive immune system. It causes a variety of symptoms, collectively referred to as AIDS (Acquired Immuno-Deficiency Syndrome).

Question 27

How is HIV transmitted?

Answer 27

The transfer of bodily fluids.
- Sex.
- Shared hypodermic needles between intravenous drug users.
- Across the placenta from a mother to a baby.
- Transfused blood.

Question 28

Give the social implications of HIV/AIDS.

Answer 28

• People with HIV can be stigmatised and not find a partner, house or employment.
• Sexual activity and reproduction in a population can be reduced because of the fear of HIV.
• Depleted family income due to loss of work.

Question 29

Define immunity.

Answer 29

The ability of an organism to resist disease.

Question 30

Give examples of Active Immunity

Answer 30

Natural – The production of antibodies in response to exposure (i.e. the person has had the disease before and has made their own antibodies).
Artificial – The production of antibodies in response to the controlled exposure to a attenuated pathogen (i.e. vaccination).

Question 31

Give examples of Passive Immunity.

Answer 31

Natural – Antibodies are received from another organism (e.g. across the placenta).
Artificial – Receiving manufactured antibodies via external delivery (i.e. the person is injected with monoclonal antibodies. It provides immediate, but short term, immunity).

Question 32

What are the benefits and dangers of vaccination?

Answer 32

Benefits:
- Prevents epidemics/pandemics and can eradicate diseases.
- Prevents deaths.
- Prevents disability, thus decreasing health care cost.
- Provides herd immunity to individuals who are unable to be vaccinated or are susceptible.

Dangers:
- Vaccinations can cause an anaphylactic reaction however this is extremely rare.

Question 33

What is the principle of vaccination?

Answer 33

To induce protection against a pathogen by stimulating an immune response similar to natural infection.

Question 34

How do blood type transfusions work?

Answer 34

A, B and O alleles all produce a basic antigen on the surface of red blood cells however the structure of this antigen varies based on the allele. Humans produce antibodies against foreign antigens so blood transfusions are not compatible between certain blood groups. An incompatible blood transfusion causes haemolysis (the destruction of red blood cells) as the body reads the donor blood cells as antigens and produces antibodies to destroy them.

Question 35

What are antibiotics?

Answer 35

Compounds that kill or inhibit the growth of microbes (specifically bacteria) by targeting prokaryotic metabolism. They destroy the bacteria’s plasma membrane and cell wall, thus interfering with DNA replication and binary fission, inhibiting the bacteria’s metabolism. This kills the bacteria or slows its growth.

Question 36

Who first discovered penicillin and how?

Answer 36

In 1928 Alexander Fleming discovered mould growing on a glass dish which killed the bacteria he was cultivating. He concluded that the mould was releasing a substance (penicillin) that was killing the nearby bacteria.

Question 37

Describe Florey and Chain’s experiments

Answer 37

In the test, eight mice were injected with a lethal bacteria with four of these mice also being injected with doses of penicillin. The untreated mice died of bacterial infection while those treated with penicillin all survived – demonstrating its antibiotic potential.

Question 38

Describe antibiotic resistance causes and effects

Answer 38

Antibiotic resistance is caused by the misuse and overuse of antibiotics. It causes higher medical costs, prolonged hospital stays and increased mortality rates because the bacterial infection is harder to treat.

Question 39

Give an example of antibiotic resistance in bacteria

Answer 39

Golden staph causes infection to the skin as well as other infections like meningitis. Historically, it was treated with medicillin. However, bacterial strains developed that were resistant to this antibiotic (called MRSA). MRSA infections are predominantly present in nursing homes where medicillin was used. It is antibiotic resistant so a post operative infection can be fatal.

Question 40

How are monoclonal antibodies produced?

Answer 40

An animal, typically a mouse, is injected with the antigen that corresponds to the desired antibody. The B-cells that produce the antibodies are extracted and fused with cultivated tumour cells to produce hybridomas. The hybridomas are capable of producing large quantities of monoclonal antibodies which can be extracted and purified.

Question 41

Treatment use of monoclonal antibodies.

Answer 41

Monoclonal antibodies are used to treat various cancers and autoimmune diseases. They can be used as an effective emergency treatment.

Question 42

How are monoclonal antibodies used in pregnancy test kits?

Answer 42

Monoclonal antibodies can be used to test pregnancy through the presence of the HCG hormone in urine.

Question 43

Define toxins.

Answer 43

A naturally occurring organic poison which is toxic to humans.