Cell recognition and the immune system

Question 1

What are the bodies non-specific defence mechanisms?

Answer 1

• physical barriers
• phagocytosis

Question 2

What are the bodies physical barriers?

Answer 2

• skin
• stomach acid
• gut and stomach flora

Question 3

What are the bodies specific defense mechanisms?

Answer 3

• cell - mediated response
• humoral response

Question 4

What type of lymphocytes carry out each specific defense mechanism?

Answer 4

• cell - mediated = T lymphocytes
• humoral = B lymphocytes

Question 5

How do lymphocytes distinguish between self and non - self cells?

Answer 5

• each cell has specific molecules on its surface that identify it as their proteins have a highly specific tertiary structure which distinguishes them
• this allows the immune system to identify pathogens, non - self cells, toxins and abnormal cells

Question 6

How do lymphocytes recognise their self cells?

Answer 6

• in the fetus lymphocytes constantly collide with other cells
• as infection in the fetus is rare, the lymphocytes collide with the bodies own self cells
• the lymphocytes that have a specific shape to these body cells bind and are killed/supressed
• therefore, the only lymphocytes left only bind to foreign cells
• this is the same for adults except it occurs in the bone marrow

Question 7

What is the first step of phagocytosis?

Answer 7

• the phagocyte is attracted to the pathogen by the chemical products of the pathogen. It moves towards the pathogen along a concentration gradient

Question 8

What is the second step of phagocytosis?

Answer 8

• Lysosomes within the phagocyte then engulf the pathogen which forms a phagosome

Question 9

What is the third step of phagocytosis?

Answer 9

• enzymes known as lysozymes within lysosomesa destroy the pathogen by hydrolysing their cell walls

Question 10

What is the fourth step of phagocytosis?

Answer 10

• the products of the breakdown are then absorbed into the cytoplasm of a phagocyte