Cell Recognition and the Immune System

Question 1

What is the non-specific immune response?

Answer 1

It is the immediate response to a pathogen and is the same for all pathogens. Includes phagocytosis.

Question 2

What is the specific immune response?

Answer 2

It is the slower response to a pathogen and is the specific to each pathogens. Includes the cell response and the humoral response.

Question 3

In what ways does your body try to prevent pathogens from invading?

Answer 3

1. Lysozymes in tears and saliva breaks down pathogens.
2. Mucus membranes on respiratory and reproductive systems
3. Acid in the stomach
4. Skin
5. Immune system

Question 4

How do phagocytes engulf and destroy pathogens?

Answer 4

1. Phagocyte engulfs pathogen in endocytosis
2. Pathogen is put in a vesicle
3. Lysosomes containing digestive enzymes (lysozymes) fuse with vesicle
4. Pathogen is hydrolysed and digested
5. Waste is released via exocytosis and the pathogens antigen is presented on the phagocytes cell membrane

Question 5

What is cell mediated immunity?

Answer 5

T-lymphocytes respond to an organisms own cells that have been invaded by external material e.g. a virus.

Question 6

How do T-lymphocytes tell invader cells apart from normal cells?

Answer 6

A pathogens antigens are presented on the phagocyte cell surface and T-lymphocytes have protein receptors on their surface that are complimentary to the antigen.

Question 7

What do T-helper cells do?

Answer 7

They activate B cells and make memory cells.

Question 8

What do T-cytotoxic cells do?

Answer 8

They release chemicals that kill infected body cells by damaging cell membranes.

Question 9

How do cytotoxic T cells destroy infected cells?

Answer 9

They produce a protein that makes holes on the cell surface membrane of the infected cell, making the membrane freely permeable, which is very effective against viruses.

Question 10

What are B cells?

Answer 10

They are a type of white blood cell covered with antibodies. These bind to antigens to form antigen-antibody complexes.

Question 11

What happens when B cells are activated?

Answer 11

They produce plasma B cells by mitosis, which are identical clones of the B cell. These secrete antibodies that are specific to the antigens. These are called monoclonal antibodies.

Question 12

What do monoclonal antibodies do?

Answer 12

They bind to the antigens on the surface of the pathogen, forming antigen-antibody complexes. They have two binding sites so can bind to two antigens at once and clump them together. This is called agglutination. These clumps are them engulfed by phagocytes.

Question 13

What is agglutination?

Answer 13

When antibodies binds to antigens, clumping them up with their two binding sites.

Question 14

Describe the cell mediated response. (4)

Answer 14

• Bind to antigen presenting cells
• Divide by mitosis
• T helper cells produce chemicals which cause B lymphocytes to divide in mitosis
• T cytotoxic cells produce chemicals that kill pathogens or infected cells

Question 15

Describe the humoral response (4)

Answer 15

• T helper cells produce chemicals to aid mitosis in B cell activation
• Memory cells are made for future infections
• Plasma cells are made to make antibodies
• Antibodies bind to pathogens

Question 16

What is the structure of an antibody?

Answer 16

• They are proteins made of chains of amino acids.
• Their specificity depends on their variable region.
• Each antibody has a unique variable region due to its tertiary structure, making them complimentary to one type of antigen only.
• All antibodies have the same constant region

Question 17

Describe how phagocytosis of a virus leads to presentation of its antigens

Answer 17

1. Phagosome/vesicle fuses with lysosome
2. (Virus) destroyed by lysozymes/hydrolytic enzymes
3. Peptides/antigen (from virus) are displayed on the cell membrane;

Question 18

Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen.

Answer 18

1. Helper T cell/TH cell binds to the antigen (on the antigen-presenting cell/phagocyte)
2. This helper T/TH cell stimulates a specific B cell
3. B cell clones OR B cell divides by mitosis 4. (Forms) plasma cells that release antibodies;

Question 19

Some white blood cells are phagocytic. Describe how these phagocytic white blood cells destroy bacteria.

Answer 19

1.Phagocyte attracted to bacteria by chemicals / recognise antigens on bacteria asforeign
2. Engulf / ingest bacteria
3. Bacteria in vacuole / vesicle
4. Lysosome fuses with / empties enzymes into vacuole
5. Bacteria digested / hydrolysed;

Question 20

Vaccines protect people against disease. Explain how.

Answer 20

1. Vaccines contain antigens / dead / weakened pathogens / antigens dead / weakened pathogens are injected
2. Memory cells made
3. On second exposure memory cells produce antibodies
4. Idea of memory cells responding
5. Rapidly produce antibodies / produces more antibodies.
6. Antibodies destroy pathogens;

Question 21

HIV can only infect cells that express the CD4 cell-surface receptor, such as T-cells. Explain why.

Answer 21

The attachment protein on the virus have a specific tertiary structure which allows them to bind to the complementary CD4 receptor but not any other receptors.

Question 22

Phagocytes and lysosomes are involved in destroying microorganisms. Describe how. (3)

Answer 22

1. (Phagocyte engulfs) to form vacuole / vesicle / phagosome;
   Accept surrounds bacteria with membrane
2. Lysosome empties contents into vacuole / vesicle / phagosome;
   Accept joins / fuses
3. (Releasing) enzymes that digest / hydrolyse bacteria;
   Ignore breakdown / destroy / lytic enzymes

Question 23

When a pathogen enters the body it may be destroyed by phagocytosis.
Describe how. (4)

Answer 23

1. Phagocyte attracted by a substance / recognises (foreign) antigen;
   Accept named substance eg chemical / antigen
2. (Pathogen)engulfed / ingested;
   Accept: description
3. Enclosed in vacuole / vesicle / phagosome;
4. (Vacuole) fuses / joins with lysosome;
5. Lysosome contains enzymes;
   Accept named example of enzyme
6. Pathogen digested / molecules hydrolysed;
   Neutral: Destroyed

Question 24

Describe the difference between active and passive immunity. (5)

Answer 24

1. Active involves memory cells, passive does not;
2. Active involves production of antibody by plasma cells / memory cells;
3. Passive involves antibody introduced into body from outside / named source;
4. Active long term, because antibody produced in response to antigen;
5. Passive short term, because antibody (given) is broken down;
6. Active (can) take time to develop / work, passive fast acting.

Question 25

Describe how B-lymphocytes respond when they are stimulated by antigens. (4)

Answer 25

1. Divide by mitosis / form clones;
2. Produce plasma cells; (plasma cells)
3. Make antibodies;
4. (Plasma cells) produce memory cells;

Question 26

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how. (5)

Answer 26

1. Vaccine contains antigen from pathogen;
2. Phagocyte presents antigen on its surface;
3. T cell with complementary receptor protein binds to antigen;
4. T cell stimulates B cell;
5. (With) complementary antibody on its surface;
6. B cell secretes large amounts of antibody;
7. B cell divides to form clone all secreting / producing same antibody

Question 27

Bacterial meningitis is a potentially fatal disease affecting the membranes around the brain. Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis.
In the UK, children are vaccinated against this disease. Describe how vaccination can lead to protection against bacterial meningitis. (5)

Answer 27

1. Antigen on surface of N. meninigitidis / bacterium binds to surface protein / surface receptor on a T cell.
2. (Activated) T cell divides by mitosis / produces clone;
3. (Division) stimulated by cytokines / by B cells;
4. B cells / plasma cells release antibodies;
5. (Some) B cells become memory cells;
6. Memory cells produce plasma / antibodies faster

Question 28

Describe how humans produce antibodies against a pathogen such as Salmonella. (6)

Answer 28

1. Salmonella pathogen has specific antigen on surface;
2. Salmonella pathogen engulfed by phagocyte;
3. T-cells activate B-cells;
4. B-cell with complementary/specific receptor antibody activated/
   clonal selection;
5. B-cells divide/form clone/clonal expansion;
6. Plasma cells make antibodies;
7. Specific to antigen/bind to salmonella bacterial antigen;
   Accept macrophage presents antigen to T/B cells;
   Accept T-cells release factors;