Download doc 3.2.4 immunity notes Student notes for section 3.2.4

3.2.4 Cell recognition and the immune system
14/05/2017
Cell recognition and the immune system
Prior knowledge from GCSE:
What is a pathogen?.................................................................................................
How do white blood cells defend against pathogens?
…………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………
How do vaccinations work?
…………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………
Cell recognition
Prior knowledge from A level cells topic – in the space below draw and label a
diagram of the cell-surface membrane.
The proteins and glycoproteins in the cell membrane of a cell help to identify it.
Natural defence mechanisms
The human body has a range of defences to protect itself from pathogens.
Non-specific mechanisms do not distinguish between one type of pathogen and
another. They include:
1................................................................................................................................
..................................................................................................................................
Page 1 of 10
3.2.4 Cell recognition and the immune system
14/05/2017
2................................................................................................................................
..................................................................................................................................
3................................................................................................................................
..................................................................................................................................
4................................................................................................................................
..................................................................................................................................
Phagocytosis
See separate sheet.
The immune system
Specific mechanisms do distinguish between different pathogens, and involve
white blood cells called lymphocytes.
Copy summary diagram figure 2 from page 103.
The immune response to invading microorganisms (the specific immune response)
is triggered by antigens.
Antigen = antibody generator
These are complex molecules (proteins, polysaccharides or glycoproteins) found on
the surface of cells which trigger antibody production. An antigen must be
Page 2 of 10
3.2.4 Cell recognition and the immune system
14/05/2017
recognised by the immune system as “non-self” – this is to prevent the body
destroying its own cells.
Antigens can be found:
 On the cell surface of bacteria
 On the surface of a virus
 On the cell surface of a tissue or organ transplant
 As a free molecule e.g. a toxin
Antibody structure and function
Antibodies are molecules released into the bloodstream which bind with antigens.
Antibodies consist of two heavy protein
chains forming a Y shape connected by a
disulphide bond. Two light chains are
attached to the arms of the Y shape, also
by disulphide bonds. The variable
regions consist of different amino acids
which allow the antibody to attach to a
particular antigen. This forms an
antibody-antigen complex.
B lymphocytes:
Are derived from stem cells in the bone marrow.
These cells secrete antibodies into the blood plasma, tissue fluid and lymph once
they are activated. Plasma cells actively secrete antibodies. Memory cells are
inactive cells ready to be activated should the need arise.
T lymphocytes:
These get their name from the fact that they are activated by the thymus gland.
T helper cells (TH cells) : These cells activate the B lymphocytes to divide and
become plasma cells.
T killer cells, also called cytotoxic T cells (TC cells) : These kill infected cells.
Humoral immunity – B cells
Use information on page 110 to produce a flow chart / diagram showing how B cells
are involved in immunity on the next page.
You should learn the 7 points on page 110
Page 3 of 10
3.2.4 Cell recognition and the immune system
14/05/2017
How antibodies kill bacteria:
 They make pathogens clump together – agglutination see diagram p.112
 Antitoxins neutralise the toxins produced by bacteria.
 Lysis digests the bacterial membrane, killing the bacterium.
 They coat the pathogens in proteins which stimulate phagocytosis.
Page 4 of 10
3.2.4 Cell recognition and the immune system
14/05/2017
Cell mediated immunity – T cells
Use information on page 107 to produce a diagram / flowchart showing how T cells
are involved in immunity:
You should learn the five points on page 107.
Page 5 of 10
3.2.4 Cell recognition and the immune system
Humoral Immunity
14/05/2017
Cell mediated immunity
Main cells
involved
Where do cells
develop?
Antibodies?
How are
pathogens
identified?
How are
pathogens
killed?
How do cells
divide once they
are stimulated?
Secondary immune response and antigenic variability
When a bacterial infection occurs and
an antigen is presented for the first
time, time is taken for the B and T
cells to multiply. Once the B cells
have differentiated into plasma cells,
specific antibodies can be secreted.
This primary response lasts several
days or weeks and then the
concentration of antibody decreases.
B memory cells are left in the body.
The memory cells will enable us to produce a fast and massive response to any later
attack by the infectious organism so that disease symptoms rarely appear twice.
So why do we suffer from colds and flu more than once in our lives?
…………………………………………………………………………………………………………………
Page 6 of 10
3.2.4 Cell recognition and the immune system
14/05/2017
…………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………
Vaccination
What is the difference between passive immunity and active immunity?
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
Do these statements refer to active immunity, passive immunity, or both?
- Antibodies rapidly produced on re-infection by same pathogen……………………..
- An antibody reacts with an antigen………………………..
- Antibodies received in breast milk……………………………
- Attenuated microorganisms in a vaccine…………………………
Definition of vaccination:
..................................................................................................................................
..................................................................................................................................
Page 7 of 10
3.2.4 Cell recognition and the immune system
14/05/2017
This is achieved by injecting small amounts of antigen - the vaccine - into the body
of an individual. The small dose of antigen is usually safe because the pathogen is
either killed or attenuated (weakened).
This ensures that the individual does not contract the disease itself, but is
stimulated to manufacture antibodies against the antigen.
Did you know?
Three million children die each year because they have not been vaccinated against
preventable diseases like measles.
Read about vaccination page 115-118
Are vaccines safe to use?
The live vaccines present the highest risk because it is always possible that a
mutation may occur that reverts the non-virulent strain to virulence or that a
particular individual will be susceptible to the non-virulent strain.
Killed vaccines have had safety problems when the lethal treatment failed to kill
100% of the microbes.
The use of chemical components of pathogens also carries some risks. Some
people may have an allergic reaction to these.
Two controversial vaccines – MMR and HPV. It’s worth keeping an eye out for news
stories about these. There is further reading on page 118.
Monoclonal antibodies
Read about monoclonal antibodies page 112-114, pay attention to the ethical
issues.
Page 8 of 10
3.2.4 Cell recognition and the immune system
14/05/2017
HIV
Draw a simple diagram to show HIV structure in the space below, and label the
components of the virus.
Summarise answers to the following:
1) How HIV replicates
2) How HIV causes the symptoms of AIDS
3) How the ELISA test can be used to detect HIV infection
Page 9 of 10
3.2.4 Cell recognition and the immune system
14/05/2017
4) Why antibiotics are ineffective against viral disease
Further reading and questions:
Chapter 5 in textbook. Summary questions pages 103, 105, 108, 110, 114, 117, 121
End of chapter questions page 122.
Extract from “Bad Science” on MMR controversy:
http://www.badscience.net/2008/08/the-medias-mmr-hoax/
Page 10 of 10