Immune System

Question 1

Purpose of the Immune System

Answer 1

To protect the body against harm (caused by infection) of small microorganisms called pathogens

Question 2

Natural barriers against infection

Answer 2

Skin: a physical barrier which secretes antimicrobial substances
blood clotting: seals wounds to prevent infection
Phagocytosis: engulfs and digests any foreign bodies in the blood
Inflammation: helps to isolate foreign substances and prevents further contact with the body
Mucus: mucous membranes of the respiratory system release mucus to waft mucus inhaled
Lysozymes: found in tears, saliva and stomach acid which kill bacteria

Question 3

Phagocytosis

Answer 3

-Phagocyte recognises foreign antigens & receptors bind to it
- cytoplasm moves around and engulfs the pathogen (it’s now present as a phagosome)
- A lysosome fuses with the phagosome to form a phagolysosome
- Lysozymes hydrolyse the pathogen in the phagolysosome
- Soluble debris exists the cell via exocytosis
- Phagocyte displays the pathogens antigen on it’s surface

Question 4

Inflammation

Answer 4

• At a wound, damaged cells release a chemical (histamine)
• These chemicals caused blood vessels to leak fluid into the tissues leading to swelling
  -This helps to isolate and prevent the pathogen from making further contact with the body
• They also attract phagocytes (WBC)

Question 5

Antibody

Answer 5

Proteins synthesised by B cells which are specific to 1 antigen, they bind to form an antigen antibody complex

Question 6

Aggulation

Answer 6

-antigens bind to two antigens at a given time forming antigen antibody complexs
-this leads to pathogens clumping up (angulation)
-This makes pathogens easier to find and phagocytosis to take place

Question 7

Cell mediated immune response (T lymphocytes)

Answer 7

Specific (helper) T cells with complementary receptors bind to antigen on antigen presenting cell
This activates the T cells to divide by mitosis, stimulate B cells & phagocytes

Question 8

Types of T lymphocytes

Answer 8

• Helper T cells: activate B lymphocytes & stimulate phagocytosis
• Cytotoxic T cells: create pores in plasma membrane of pathogens by producing perforin
• Memory T cells: remain in blood until another infection, they then divide rapidly by mitosis

Question 9

Humoral Response (B Lymphocytes)

Answer 9

• B lymphocyte cells are covered in receptors for their specific antigen
• Once they find the complementary receptor, their stimulated by helper T cells (that release cytokines)
• They differentiate into plasma or memory b cells

Question 10

Type of B lymphocytes

Answer 10

-Plasma Cells: rapidly produce antibodies which cause antigens to become inactivated
- memory cells: remain in blood circulation (for years) until the same antigen appears, they then rapidly divide by mitosis

Question 11

Primary vs Secondary exposure

Answer 11

The second exposure produces antibodies faster and at a higher rate, as the antigens are detected and memory cells can rapidly undergo mitosis to produce antibodies

Question 12

Lag time

Answer 12

The time at the primary exposure when the correct complementary antibody is being found for the pathogens antigens