3.2.4 Cell Recognition and the Immune System

Question 1

What is an antigen?

Answer 1

Any part of an organism or substance that is recognised as non-self by the immune system and stimulates an immune response
Usually proteins that are a part of the cell-surface membrane or cell walls of invading cells

Question 2

What is non-specific immunity?

Answer 2

Includes physical barriers and phagocytosis

Question 3

What is the physical barrier of immunity?

Answer 3

Mucous membranes: mucous traps pathogens
Dead skin cells block pathogens
Hydrochloric acid kills pathogens in the stomach

Question 4

What is a phagocyte?

Answer 4

Cells which engulf pathogens
They move through blood and lymph into connective tissue

Question 5

What is the process of phagocytosis?

Answer 5

Phagocyte is attracted to the pathogen by chemical products of the pathogen along a concentration gradient
The phagocytes has several receptors on its cell surface membrane that attach to chemicals on the surface of the pathogen
Lysosomes within the phagocyte migrate towards the phagosome formed by engulfing the bacterium
The lysosomes release their lysozymes into the phagosome, where they hydrolyse the bacterium
The hydrolysis products of the bacterium are absorbed by the phagocyte

Question 6

What is specific immunity?

Answer 6

Cell mediated response and humoral response

Question 7

What is the process of B cells?

Answer 7

1. The surface antigens of an invading pathogen are taken up by a B cells
2. The B cell processes the antigens and presents them on its surface
3. Helper T cells attach to the processed antigens on the B cells thereby activating the B cell
4. The B cell is now activated to divide by mitosis to give a clone of plasma cells
5. The cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogens surface
6. The antibody attaches to antigens on the pathogen and destroys them
7. Some B cells develop into memory cells. These can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies. This is the secondary immune response

Question 8

What is the process of T helper cells?

Answer 8

Associated with cell-mediated immunity
1. Mature in the thymus gland
2. Bacteria has foreign antigens on its surface
3. Pathogens invade body cells or are taken in by phagocytosis
4. The phagocyte places antigens from the pathogen on its cell-surface membrane
5. Receptors on a specific helper T cell fit exactly onto these antigens
6. The attachment activates the T cell to divide rapidly by mitosis and form clones of genetically identical cells
7. The cloned cell:
Develop into memory cells that enable a rapid response to future infections by the same pathogen
Stimulate phagocytes to engulf pathogens by phagocytosis
Stimulate B cells to divide and secrete their antibody
Activates cytotoxic T cells

Question 9

How do cytotoxic T cells kill infected cells?

Answer 9

They produce a protein called perforin which makes holes in the cell-surface membrane
These holes make the membrane freely permeable
The cell dies as a result
Associated with cell-mediated immunity

Question 10

What is the structure of an antibody?

Answer 10

See card

Question 11

How does agglutination occur?

Answer 11

Each antibody binds to two pathogens due to its two active sites
This clumps the pathogens together to make them easier to engulf by phagocytes

Question 12

What is an antibody?

Answer 12

A protein produced by lymphocytes in response to the presence of the appropriate antigen

Question 13

Why are monoclonal antibodies needed?

Answer 13

A pathogen has many different proteins on its surface, all of which act as antigens
Each toxin molecule also acts as an antigen
Therefore many different B cells make clones, each of which produces different antibodies
These antibodies are called monoclonal antibodies as they’re antibodies which all work on the same pathogen

Question 14

What is direct monoclonal antibody therapy?

Answer 14

Monoclonal antibodies are produced that are specific to cancer cells
Antibodies are given to a patient which attaches themselves to receptors on cancer cells
They attach to the surface of the cells and block chemical signals that stimulate uncontrolled growth

Question 15

What is the ELISA test?

Answer 15

Using antibodies to detect antigens in a sample of blood/urine, combined with an enzyme that will give a colour change

Question 16

How are monoclonal antibodies used in pregnancy tests?

Answer 16

A hormone (HCG) is released by the placenta during pregnancy which is excreted in the urine
Monoclonal antibodies show its presence

Question 17

Do vaccines work if you have an autoimmune disease?

Answer 17

No because no antibodies are produced and so the person will not be immune to the disease

Question 18

What does a vaccine do?

Answer 18

It can’t stop the pathogen from entering your body but it stops you from experiencing any symptoms because the pathogen is defeated too quickly

Question 19

How does a vaccine work?

Answer 19

It contains dead or inactive pathogen cells
The immune system destroys the pathogen easily
The memory cells remember the antibodies used so that it can kill the pathogen if it returns

Question 20

What are the ethical issues of vaccinations?

Answer 20

Children that are vaccinated can’t consent

Question 21

What are the ethical issues of monoclonal antibodies?

Answer 21

Tested on animals

Question 22

What is passive immunity?

Answer 22

Antibodies that aren’t made by the individual are given to them
E.g. mammals through the placenta

Question 23

What is active immunity?

Answer 23

Memory cells and antibodies are made by the individual infected either naturally or following a vaccination

Question 24

Why do vaccinations need to be repeated?

Answer 24

A booster allows for a better immune response because the pathogen could overwhelm the immune response and cause symptoms

Question 25

What is the structure of HIV?

Answer 25

Capsid: protein coat which protects RNA within
Viral envelope: a piece of the cell membrane budded off from the last human host cell
Nucleic acid: RNA containing genetic blueprint
Reverse transcriptase: enzyme which converts DNA into RNA once inside a host cell
Surface proteins: spikes which allow HIV to attach to host cells

Question 26

How does HIV replicate inside T helper cells?

Answer 26

It can’t replicate himself so uses the host cell’s machinery
1. HIV enters the bloodstream and circulates
2. Protein on the HIV readily binds to (mostly) helper T cells
3. Protein capsid fuses with the cell-surface membrane. RNA and enzymes of HIV enter the helper T cell
4. HIV reverse transcriptase converts the virus’s RNA into DNA
5. DNA moves into the helper T cell nucleus and is inserted into the cell’s DNA
6. HIV DNA creates messenger RNA using the cell’s enzymes
7. mRNA passes out of the nucleus through a nuclear pore
8. The cell’s protein synthesis mechanisms use the mRNA to make HIV particles
9. HIV particles break away from the host with a piece of its cell-surface membrane surrounding them to form the lipid envelope

Question 27

What are the stages from HIV to AIDS?

Answer 27

1. Few/no symptoms, infection can spread
2. Free from symptoms, low level of HIV in blood, lasts for 10 years, HIV antibodies are detected in the blood
3. Mild symptoms, immune system deteriorates, opportunistic infections
4. Opportunistic infections cause AIDS

Question 28

How is HIV spread?

Answer 28

Bodily fluids
E.g. sexual intercourse, infected needles, blood transfusions,

Question 29

What is the structure of an antibody?

Answer 29

See card

Question 30

What is an infection?

Answer 30

An interaction between the pathogen and the body’s various defence mechanisms

Question 31

How can lymphocytes distinguish between the body’s cells and foreign cells?

Answer 31

The highly specific protein molecules on the cell surface membrane

Question 32

What are the two types of defence mechanisms against pathogens?

Answer 32

Non-specific (same for every pathogen): physical barriers and phagocytosis
Specific (specific to each pathogen): response is slower, cell-mediated response by T lymphocytes, humoral response by B lymphocytes

Question 33

What happens to lymphocytes with receptors matching those of the host’s body?

Answer 33

In the foetus: lymphocytes either die or are suppressed
In the bone marrow: undergo programmed cell death (apoptosis) before they differentiate

Question 34

What are the two types of white blood cells?

Answer 34

Phagocytes and lymphocytes

Question 35

What is the function of phagocytes?

Answer 35

To ingest and destroy pathogens via phagocytosis

Question 36

What is immunity?

Answer 36

The ability of organisms to resist infection by protecting against disease-causing microorganisms or their toxins that invade their bodies
It involves the recognition of foreign material

Question 37

What are the two types of lymphocytes?

Answer 37

B lymphocytes: mature in the bone marrow, associated with humoral immunity (antibodies present in bodily fluids)
T lymphocytes: mature in the thymus gland, associated with cell-mediated immunity (immunity involving body cells)

Question 38

How can T lymphocytes determine whether a body cell has been infected with non-self material?

Answer 38

Phagocytes that have engulfed a pathogen and body cells invaded by viruses present some of the antigens on their cell-surface membrane
Transplanted cells from members of the same species and cancer cells present different antigens on their cell-surface membranes

Question 39

What is the name for cells that display foreign antigens on their surface?

Answer 39

Antigen presenting cells

Question 40

What do T lymphocytes respond to?

Answer 40

Antigens that are presented on a body cell rather than to antigens within bodily fluids
This is called cell-mediated immunity
The receptors on each at cell respond to a specific antigen

Question 41

What microorganisms are T cells most effective against?

Answer 41

Viruses because they replicate inside cells so the sacrifice of body cells prevents viruses from multiplying

Question 42

Why is humoral immunity called as such?

Answer 42

It involves antibodies
Antibodies are soluble in the blood and tissue fluid of the body

Question 43

What are plasma cells?

Answer 43

Cells which secrete antibodies usually into blood plasma
They rapidly produce antibodies during its brief lifespan
The antibodies lead to the destruction of the pathogen
Production of antibodies and memory cells is known as the primary immune response

Question 44

What are memory cells?

Answer 44

Secondary immune response
Live longer than plasma cells
Divide rapidly at a later date to produce plasma and memory cells when encountering an antigen
Provide long-term immunity
Ensures a fast response so that symptoms do not arise