Chapter 5- Cell Recognition And The Immue System

Question 1

What are the two types of defence mechanism and what does each include?

Answer 1

1. Non-specific - immediate + same for all pathogens -> physical barriers + phagocytosis
2. Specific - slower + specific to each pathogen -> cell-mediated response + humoral response

Question 2

What are phagocytes?

Answer 2

White blood cells which carry out phagocytosis

Question 3

Process of phagocytosis

Answer 3

1. Phagocyte attracted to pathogen by chemical products
2. Phagocyte attaches to surface of pathogen using their receptors
3. Phagocyte engulfs the pathogen - forming a vesicle (phagosome)
4. Lysosomes move towards vesicle + fuse with it
5. Lysosomes release lysozymes which hydrolyse the pathogen
6. Products of the hydrolysis are absorbed by the phagocyte

Question 4

Antigen

Answer 4

Part of an organism/substance that is recognised as foreign and it stimulates an immune response

Question 5

Cell-mediated immunity

Answer 5

1. Pathogens invade body cells / taken in by phagocytosis
2. Phagocyte places antigens from pathogen on cell-surface membrane - becomes antigen-presenting cell
3. Receptors on specific helper T cell fix exactly onto these antigens
4. This activates the T cell to divide rapidly by mitosis - forms clones of genetically identical cells
5. Cloned T cells either: become memory cells, stimulate phagocytes, stimulate B cells, activate cytotoxic T cells

Question 6

How do cytotoxic T cells kill infected cells?

Answer 6

Produce perforin - makes holes in cell-surface membrane - cell membrane becomes freely permeable - cell dies

Question 7

What is the purpose of plasma cells?

Answer 7

-Secrete antibodies into blood plasma -> leads to destruction of the antigen
-Responsible for immediate defence of the body

Question 8

What do memory cells do?

Answer 8

-Secondary immune response
-Circulate ready to produce more memory cells + plasma cells -> contribute to long-term immunity

Question 9

Humoral immunity

Answer 9

1. Surface antigens of invading pathogen taken up by a B cell
2. B cell processes antigens + presents them on its surface
3. Helper T cells attach to processed antigens on B cell -> activates B cell
4. B cell now divides by mitosis to give a clone of B cells
5. Cloned plasma cells = secrete specific antibodies to fit the antigen on the pathogen
6. Antibody attaches to antigens on pathogen + destroys them
7. Some B cells -> memory cells -> secondary immune response

Question 10

Structure of an antibody

Answer 10

4 polypeptide chains
2 heavy chains + 2 light chains
Binding site is different on different antibodies = variable region
Rest of antibody = constant region

Question 11

Where does the antigen bind to the antibody and what does it form?

Answer 11

Binds at the specific binding site in the variable region
Forms an antigen-antibody complex

Question 12

2 ways that antibodies lead to the destruction of antigens

Answer 12

1. Agglutination - clumps of cells formed, phagocytes can locate them
2. Act as markers - stimulate phagocytes to engulf

Question 13

What are monoclonal antibodies?

Answer 13

A single, specific type of antibody that has been isolated and cloned