5-Cell Recognition & Immune System

Question 1

Non Specific Defence Mechanisms

Answer 1

An immediate response and is the same for all pathogens; physical barriers like skin, or phagocytosis.

Question 2

Specific Defence Mechanisms

Answer 2

A slower response but specific to each pathogen: a cell mediated response (T lymphocytes) or a humoral response (B lymphocytes)

Question 3

Lymphocytes

Answer 3

A type of white blood cell involved in immune responses.

Question 4

Phagocytes

Answer 4

A type of white blood cell which destroy pathogens by ingesting them before they cause any harm.

Question 5

Phagocytosis

Answer 5

1) Phagocyte is attracted to pathogen.
2) Phagocyte’s receptors on its surface attach to chemicals on surface of pathogen.
3) Lysosomes in phagocyte migrate to phagosome formed by engulfing the bacteria.
4) Lysosomes release lysozymes which hydrolyse bacterium.
5) The products of hydrolysis are absorbed by the phagocyte.

Question 6

Antigens

Answer 6

Any part of an organism that’s recognised as non self (foreign) by the immune system and simulates an immune response.

Question 7

B Lymphocytes (B cells)

Answer 7

Lymphocytes that mature in the bone marrow and are associated with humoral immunity (immunity involving antibodies present in body fluids/humour in blood plasma).

Question 8

T Lymphocytes (T cells)

Answer 8

Lymphocytes that mature in the thymus gland and are associated with cell-mediated immunity involving body cells.

Question 9

Cell-mediated Immunity

Answer 9

1) Pathogens invade body cells/are taken in by phagocytes.
2) Phagocyte places antigen from pathogen on its cell-surface membrane.
3) Receptors on a specific helper T cell fit exactly onto these antigens.
4) This attachment causes T cells to divide rapidly by mitosis and form clones of genetically identical cells.
5) The cloned T cells develop into memory cells for a future rapid response, stimulate phagocytosis, stimulate B cells to secrete their antibodies, activate cytotoxic T cells.

Question 10

Humoral Immunity

Answer 10

1) B cell takes the antigens of an invading pathogen.
2) B cell processes antigens and presents them on its surface.
3) Helper T cells attach to processed antigens on B cell and activate it.
4) Activated B cells divide by mitosis and give a clone of plasma cells.
5) Cloned plasma cells secrete antibodies that fit to antigen on the pathogen’s surface.
6) Antibodies attach to pathogen’s antigens and destroy it.
7) Some B cells develop into memory cells for a faster secondary immune response.

Question 11

Antibodies

Answer 11

Proteins with specific binding sites synthesised by B cells. Made up of 4 polypeptide chains, 2 of which are heavy (long) and the other 2 are light (short).

Question 12

How antibodies cause the destruction of antigens

Answer 12

Cause agglutination of bacterial cells where they clump together and are easier to be located by phagocytes. They also serve as markers that stimulate phagocytes to engulf the bacterial cells.

Question 13

Monoclonal Antibodies

Answer 13

Antibodies that are made outside of the body that can be cloned.

Question 14

Monoclonal Antibodies in Pregnancy Tests

Answer 14

When pregnant the placenta produces the hormone hCG which is found in the mother’s urine. On the test strip if hCG is present then the colour complex moves down the strip until it’s trapped by a different type of antibody, creating a coloured line.

Question 15

Immunity

Answer 15

The ability of an organism to resist infection, can be active or passive.

Question 16

Passive Immunity

Answer 16

The introduction of antibodies from an outside source. No actual interaction with relevant pathogen is required to induce immunity. Since the antibodies aren’t being produced by the individual, they aren’t replaced when broken down so don’t form memory cells so there’s no lasting immunity. E.g. anti-venom for snake bites and is passed down to foetus across placenta of the mother.

Question 17

Active Immunity

Answer 17

Stimulating the production of antibodies by the individual’s own immune system. Direct contact with pathogen is necessary and immunity takes time to develop. Can be natural or artificial.

Question 18

Natural Active Immunity

Answer 18

Individual becomes infected with disease under normal circumstances. Body produces antibodies and may continue to do so for years.

Question 19

Artificial Active Immunity

Answer 19

Inducing the immune response in an individual without them suffering the symptoms of the disease (vaccination/immunisation).

Question 20

Vaccination

Answer 20

The introduction of disease antigens into an individual to stimulate an immune response against the particular disease.

Question 21

Here Immunity

Answer 21

When the majority of a population is vaccinated against a specific disease so the spread is greatly decreased, therefore the chance of a susceptible individual contracting the disease is also greatly decreased.

Question 22

Structure of Human Immunodeficiency Virus (HIV)

Answer 22

Outside lipid envelope with peg-like attachment proteins on surface. Inside the envelope is the capsid (a protein layer) that encloses 2 single strands of RNA and some enzymes. One of these enzymes is reverse transcriptase which catalyses the production of DNA from RNA. This makes HIV belong to the group of viruses called Retroviruses.

Question 23

Replication of HIV

Answer 23

1) Enters bloodstream and circulates around body.
2) Proteins on HIV bind to the protein CD4 which is mainly on T cells.
3) Capsid of HIV fuses with plasma membrane of T cell and RNA and enzymes enter T cell.
4) Reverse Transcriptase coverts virus’s RNA to DNA.
5) Newly made DNA enters nucleus of T cell.
6) HIV DNA in nucleus forms mRNA with instructions to produce new viral proteins and RNA for new virus.
7) mRNA passes through nuclear pore and uses cell’s protein synthesis mechanisms to make HIV particles.
8) HIV particles break away from T cell with a piece of its plasma membrane to form lipid envelope.

Question 24

Symptoms of Acquired Immune Deficiency Syndrome (AIDS)

Answer 24

200mm-3 of T cells, normally between 800-1200mm-3.
Can’t produce B cells or cytotoxic T cells.
Unable to produce adequate immune response.