Chapter 11: Immunity in Humans

Question 1

Pathogens can only cause diseases if they successfully _____ body cells. The body system recognises it as antigens. Antigens are foreign particles that enter the body and subsequently _____ the _____ response.
Antigens stimulate the ______ to produce antibodies into the blood flow. Antibodies are _____ found on the lymphocyte surface or released into the blood ____. The interaction between antibodies and antigens is called the ____ _____.

Answer 1

• infect
• stimulate
• immune
• lymphocytes
• proteins
• plasma
• immune response

Question 2

Immunity is the body’s ability to fight infections caused by ____ through ____ attacks. There are three lines of defence which are: _____, _____ and ____.

Answer 2

• pathogens
• specific
• first line of defence
• second line of defence
• third line of defence

Question 3

The first line of defence consists of ____ and chemical line-up that prevent pathogens from entering. It is not ____ and acts to prevent pathogens from entering the body.

Answer 3

• physical

- specific

Question 4

Explain the functions of lysozyme, mucous membrane and hydrochloric acid in the first line of defence.

Answer 4

Lysozyme
- found in tears, nasal mucus and saliva
- an antimicrobial protein that can dissolve and destroy bacteria
Mucous membrane
- found on the respiratory tract and secretes mucus
- has lysozyme that destroys bacteria found in the air
Hydrochloric acid
- destroys bacteria present in food and drinks in the stomach

Question 5

Explain the mechanism of blood clotting and the function of the skin in the first line of defence.

Answer 5

Mechanism of blood clotting
- prevents bacteria from entering through wounds
Skin
- physical defence that prevents the entry of pathogens because it is tough and difficult to penetrate
- continuous shedding of dead cell layers makes it difficult for microorganisms to grow
- acts as a chemical shield through sebum secretion
- sweat has lysozyme which can help break down the cell walls of certain bacteria

Question 6

The second line of defence is ____, ________ and _______. The mechanism of the second line of defence is not _____. Fever is the second line of defence that mechanism that fights ____. It increases ______ activity and fights against microorganisms that infect the body.

Answer 6

• fever
• phagocytosis
• inflammation
• specific
• infections
• phagocytic

Question 7

Explain phagocytosis in the second line of defence and the stages of phagocytosis.

Answer 7

• phagocyte is a leucocyte that can carry out phagocytosis ( neutrophils and monocytes )
• phagocytes move to the infection site and enter the tissue fluid through the pores of the capillary wall
• it engulfs the pathogen
  Stages
• extends its pseudopodium and engulfs it
• bacterial ingestion forms phagosome
• phagosome combines with a lysosome that secretes lysozyme inside the phagosome
• bacterium in the phagosome is destroyed
• phagocytes expels the remains of the digested microorganisms

Question 8

Explain inflammation in the second line of defence and the inflammatory response.

Answer 8

• an immediate response that destroys and neutralises harmful microorganisms actions
• the inflamed area will swell, turn red and feel painful
  Inflammatory response
• damaged tissue releases histamine which stimulates an immediate inflammatory response
• histamine causes vasodilation for more blood to flow to the infected area
• histamine also increases phagocytes permeability to blood capillaries
• phagocytes and clotting factors accumulate
• blood clotting mechanism is triggered
• phagocytosis is carried out

Question 9

Explain the third line of defence.

Answer 9

• is the immune response of the lymphocytes
• lymphocytes formed in the lymph nodes produce antibodies
• specific action as each type of antibody can only combine with a certain type of antigen
• lymphocytes accumulate during infection to destroy antigens and causes lymph nodes to swell
• lymph nodes also have macrophages that destroy bacteria through phagocytosis
• 2 types of lymphocytes which are T” and B”
• T” attacks cells infected by pathogens and it stimulates B” to produce memory cells
• memory cells stimulated to produce antibodies immediately if the same pathogen attacks

Question 10

What are the 5 mechanisms of the actions of antibodies?

Answer 10

• agglutination
• neutralisation
• precipitation
• lysis
• opsonisation

Question 11

Explain all the 5 mechanisms of antibody actions.

Answer 11

Agglutination
- antibodies coagulate the pathogens and so it would be easy to trap and destroy by phagocytes
Neutralisation
- antibodies combine with toxins produced by bacteria and neutralise the toxin
Precipitation
- antibodies react with dissolved antigens to form an insoluble complex
Opsonisation
- antibodies combine with antigens and act as a marker for phagocytes to recognise the antigens and destroy them
Lysis
- “ “ “ “ and cause bacteria to be broken down and decomposed