06. Responding to antigens

Question 1

Describe how intact skin works to prevent disease.

Answer 1

A physical barrier. This means that it prevents entry of pathogens into the body.

Question 2

Define pathogen

Answer 2

Disease causing agent

Question 3

Define disease

Answer 3

A physical or mental disturbance involving symptoms, dysfunction or tissue damage.

Question 4

Define antigen

Answer 4

An antigen is a unique molecule or part of a molecule that can initiate an immune response.

Question 5

Give 3 reasons a pathogen is described as non-cellular

Answer 5

They require a host cell as they cannot reproduce outside a host cell

No metabolic cellular processes (whilst they have DNA or RNA they have no organelles to generate energy or proteins)

Not made of cells

Question 6

Give 3 reasons a pathogen is described as cellular

Answer 6

They do not require a host cell as they can reproduce outside a host cell

Can undertake metabolic cellular processes (they have DNA or RNA and they have the organelles to generate energy or proteins)

Made of cells

Question 7

Give 2 examples of non-cellular pathogens

Answer 7

Virus and prion

Question 8

Define prion

Answer 8

Abnormal infectious protein

Question 9

Give 4 examples of cellular pathogens

Answer 9

Bacteria

Fungi

Protozoa - e.g. Plasmodium (malaria)

Parasite

Question 10

State the three types of barriers

Answer 10

Physical barriers
Chemical barriers
Microbiological barriers

Question 11

Give two examples of physical barriers in a human.

Answer 11

Intact skin
Hairs

Question 12

Give two examples of chemical barriers in a human.

Answer 12

Stomach acid, lysozymes

Question 13

Define microbiota barrier

Answer 13

Themicroorganismsin a particular location (e.g. on the skin, in the gut, in the vagina) that live in a symbiotic relationship with animals to outcompete pathogens.

Question 14

Give two examples of physical barriers in a plant

Answer 14

Intact bark
Thick waxy cuticle
Thorns or trichomes (hair like structures)
Position of stomata
Formation of galls

Question 15

State a chemical barrier in a plant

Answer 15

They can secrete many antimicrobial proteins OR secrete odour chemicals such as peppermint/caffeine.

Question 16

Describe the Rhizosphere in a plant

Answer 16

Rhizosphere is a microbiota barrier in a plant. This means that it is inhabited by a unique population of microorganisms to outcompete the pathogenic bacteria in the soil by synthesising and releasing toxins.

Question 17

Describe how hydrochloric acid works to prevent disease.

Answer 17

Chemical barrier. This means that it destroys pathogens that enter the stomach.

Question 18

Name the main components of the lymphatic system

Answer 18

Bones
Lymph vessels
Lymph fluid
Lymph nodes

Question 19

Describe the lymph

Answer 19

A colourless fluid containing white blood cells. This means that it bathes the tissues and drains through the lymphatic system into the bloodstream.

Question 20

Compare the circulatory system (the cardiovascular system) with the lymphatic system

Answer 20

Circulatory has a pump whereas lymph has no pump
Circulatory contains red blood cells (RBC) whereas lymph has no RBC
Circulatory system has (some vessels) with no valves where as all of the lymphatic vessels have valves
Circulatory system fluid is called plasma where as lymphatic system the fluid is called lymph

Question 21

Give the function of the bone marrow

Answer 21

Site where white blood cells (macrophage, neutrophil, dendritic, T and B lymphocytes) are made and mature.

Question 22

Give the function of the lymph node

Answer 22

Site of antigen recognition. This means that it is where antigen presenting cells meet T and B cells for clonal selection, differentiation and expansion of the T and B cells in the adaptive immune response.

Question 23

Describe the two functions of phagocytes

Answer 23

Phagocytosis. This means that they recognise, engulf and digest foreign material, such as pathogens.
Antigen presenting cells (macrophage or dendritic). This means that they will move from the site of infection to the lymph node to present non-self antigens on MHCII to T and B cells to initiate the adaptive immune response.

Question 24

Sate what line of defence phagocytosis is a part of

Answer 24

Second/innate/non-specific

Question 25

State what types of cells have an MHCI marker

Answer 25

All cells with a nucleus (so RBC don’t)

Question 26

Describe the steps of phagocytosis

Answer 26

1. Phagocyte recognises a non-self antigen and engulfs pathogen forming a phagosome
2. Phagosome fuses with lysosome forming a phagolysosome
3. Pathogen destroyed by digestive enzymes in lysosome
4. Destroyed pathogen removed from the cell by exocytosis

Question 27

Give three types of phagocyte

Answer 27

Neutrophil, macrophage and dendritic cell

Question 28

Describe the function of an eosinophil

Answer 28

Eosinophils are large granulated cells containing various enzymes that recognize and destroy invading pathogens which are too large to be broken down by phagocytosis. This means that mediators such as DNases, RNases, and proteases, help destroy invading pathogens.

Question 29

Give the function of a natural killer cell

Answer 29

Recognise non-self antigens on MHCI markers and release cytotoxic chemicals which destroy the virally infected or cancer cell.

Question 30

Give the functions of complement proteins

Answer 30

Chemotaxis – complement proteins gather near a pathogen and attract phagocytes to it making phagocytosis easier/
Opsonisation - attach to non-self-antigen on B cells making them easier to identify and making phagocytosis easier. [1]
Lyse B cell plasma membranes by forming a membrane attack complexes [2]
Promote inflammation by recruiting inflammatory cells which destroy the B cell.

Question 31

Describe the function of interferons

Answer 31

Interferons are secreted by cells when they are infected with a virus. This means that the interferons interact with receptors on neighbouring cells, causing them to undergo a number of changes that make them less susceptible to viral infection. This helps prevent the virus from spreading between cells.

Question 32

State the two steps which B cells need to activate in the lymph node

Answer 32

An antigen presenting cell needs to present a specific and complementary non-self antigen on an MHCII marker and this needs to bind to the antigen binding site of the antibody

Recieve a cytokine signal from a T helper cell

Question 33

State the two steps which T cytotoxic cells need to activate in the lymph node

Answer 33

An antigen presenting cell needs to present a specific and complementary non-self antigen on an MHCII marker and this needs to bind to the T cell receptor

Recieve a cytokine signal from a T helper cell

Question 34

Outline the steps of the humoral immune response in the lymph node

Answer 34

Clonal selection occurs. This means that the antigen presenting cell that has moved from the site of infection to the lymph node to present a non-self antigen on an MHCII marker to a B cell and T helper cell which causes the T helper cell to release cytokines to activate the naive B cell.

Clonal differentiation and expansion occurs. This means that the B cell divides by mitosis forming a B memory cell and a plasma cell. The plasma cell then secretes specific, complementary and free floating antibodies.

The B memory cell remains in circulation to provide long term immunity.

Question 35

Outline the functions of antibodies

Answer 35

All antibodies have a specific and complementary antigen binding site to an________ antigen so…

Agglutination of ____ pathogens occurs. This means that there are less pathogens circulating and makes phagocytosis of more pathogens easier.

Neutralisation of ____ toxins/ ____ virus occurs. This means that they become inactive and will reduce the severity of disease.

Opsonisation occurs by attaching to ____pathogens. This means that phagocytosis is more likely as they have been marked for destruction.

Activate complement proteins. This means that phagocytosis ismore likely as they have been marked for destruction.

Question 36

Describe what provides long term immunity in the humoral immune response.

Answer 36

B memory cells remain in circulation. This means that on secondary infection with the same pathogen they can divide more rapidly and lead to more B memory cells and more plasma cells which secrete a higher concentration of specific complementary and free floating antibodies more rapidly.

Question 37

Compare natural killer cells with T cytotoxic cells

Answer 37

Natural killer (NK) cells are non-specific whereas T cytotoxic (T cyto.) are specific

NK have no memory cells whereas T cyto. have memory cells
Both look for non-self antigens presented on MHCI markers.
Both release perforins/cytotoxic chemicals/death ligands to initate destroying virally infected cells or cancer cells.

Question 38

Outline the steps of inflammation.

Answer 38

Damaged cells/tissues release cytokines. These attract neutrophils to the site of infection and activate mast cells to release histamine.

Histamine causes vasodilation which is more blood flow to the area. This means that there will be more macrophages, neutrophils and dendritic cells brought to the site of infection and cause redness and an increase in temperature.

Histamine also causes an increase in membrane permeability. This means that more tissue fluid leaks out causing swelling and pain and means that the phagocytes can reach the tissues and help eliminate the pathogen by phagocytosis.

Question 39

State how antibodies attach to a non-self antigen/toxin/allergen

Answer 39

By their specific and complementary antigen binding site

Question 40

Outline the steps in the cell-mediated immune response

Answer 40

Clonal selection occurs. This means that the antigen presenting cell /macrophage/dendritic cell moves from the site of infection to the lymph node [1]
to present a non-self-antigen from coronavirus on an MHCII marker to a T cytotoxic cell and T helper cell [1]
which causes the T helper cell to release cytokines to activate the T cytotoxic cell. [1]
Clonal differentiation and expansion occurs. This means that the T cytotoxic cell divides by mitosis forming an active T cytotoxic cell and a T cytotoxic memory cell. [1]
The active T cytotoxic cell then releases cytotoxic chemicals to kill virally infected cells (once it recognises the non-self covid antigen on MHCI markers. [1]