SUMMARY QUESTIONS

Question 1

State 2 differences between a specific and a non-specific defence mechanism

Answer 1

• A specific mechanism distinguishes between different pathogens but responds more slowly than a non-specific mechanism
• A non-specific mechanism treats all pathogens in the same way but responds more rapidly than a specific mechanism

Question 2

After a pathogen gains entry to the body it is often a number of days before the body’s immune system begins to control it. Suggest a possible reason why this is so

Answer 2

The lymphocytes that will finally control the pathogen need to build up their numbers and this takes time

Question 3

After a pathogen gains entry to the body it is often a number of days before the body’s immune system begins to control it. Why would it be inaccurate to say that the body takes days to ‘respond’ to the pathogen

Answer 3

• the body responds immediately by ‘recognising’ the pathogen (and by phagocytosis)
• the delay is in the building up numbers of lymphocytes and therefore controlling the pathogen

Question 4

In the following passage, state the missing word indicated by each letter, a-d:

Pathogens that invade the body may be engulfed by cells which carry out (A). The engulfed pathogens forms a vesicle known as a (B). Once engulfed the pathogen is broken down by enzymes known as (C) released from organelles called (D)

Answer 4

A - phagocytosis
B - phagosome
C - lysozyme
D - lysosome

Question 5

Among other places, lysozymes are found in tears. Suggest a reason why this is so

Answer 5

• the protective covering of the eye, and especially the tear ducts, are potential entry points for pathogens
• therefore making the eyes vulnerable to infection because the coverings are (to allow light through)
• lysozyme will break down cell walls of any bacterial pathogens and so destroy them before they can cause harm

Question 6

Define an antigen

Answer 6

An organism or substance, usually a protein, that is recognised as foreign by the immune system and therefore stimulates an immune response

Question 7

State 2 similarities between T cells and B cells

Answer 7

• Both are types of white blood cells
• Both have a role in immunity
• Both are produced from stem cells

Question 8

State 2 differences between T cells and B cells

Answer 8

• T cells mature in the thymus gland and B cells mature in the bone marrow
• T cells are involved in cell-mediated immunity and B cells are involved in humoral immunity

Question 9

From your knowledge of of cell-mediated immunity and lung structure suggest why humans infected with the H5N1 virus may sometimes die from suffocation

Answer 9

• H5N1 infects the lungs, leading to massive production of T cells
• Accumulation of these cells may block the airways/fill the alveoli —> causing suffocation

Question 10

Suggest a reason why any spread of bird flu across the world is likely to be very rapid

Answer 10

Birds carry H5N1 virus
—> can fly vast distances across the world in a very short amount of time

Question 11

Explain why the secondary immune response is much more rapid than the primary one

Answer 11

• in the primary response, the antigens of the pathogen have to be digested, processed, then presented by B cells. T helper cells need to link with B cells that then clone, some of the cells developing into plasma cells then produce antibodies. These processes occur consecutively and therefore take time
• in the secondary response, memory cells are already present and the only processes are cloning and development into plasma cells that produce antibodies
• Fewer processes means a quicker response

Question 12

Contrast the cell-mediated and humoral responses to a pathogen

Answer 12

Cell-mediated immunity
- involves T cells / no antibodies / first stage of immune response / effective through cells

Humoral immunity
- involves mostly B cells / antibodies produced / 2nd stage of immune response (after CMI) / effective through bodily fluids

Question 13

Plasma cells can produce around 2000 protein antibodies each second. Suggest 3 cell organelles that you might expect to find in large quantities in a plasma cell, and explain why

Answer 13

• rough ER: to make and transport the proteins of the antibodies
• Golgi apparatus: to sort, process and compile the proteins
• Mitochondria: to release the energy needed for such massive antibody production

Question 14

Suggest why antibodies made of proteins, rather than carbohydrates or fats are more likely to be effective against a wide range of diseases

Answer 14

• there must be a massive variety of antibodies as each responds to a different antigen, of which there are millions
• only proteins have the diversity of molecular structure to produce millions of different types of antibodies

Question 15

Distinguish between an antigen and an antibody

Answer 15

• Antigen: a molecule that triggers an immune response by lymphocytes
• Antibody: the molecule that has a complementary shape to the antigen and is produced in response to it

Question 16

Discuss whether drug trials should be limited to volunteers who are terminally ill with a condition that the monoclonal antibody is designed to treat

Answer 16

In favour
- removes the risk of healthy volunteers being harmed
- terminally ill patients have most to gain and less to lose

Against
- response of terminally ill might be different to response to those in early stages of the disease, therefore results may be unreliable
- sample size likely to be smaller