C3.2 (1) Defense Against Infectious Diseases

Question 1

Pathogen

Answer 1

Organisms that cause disease; Reserved for viruses, bacteria, fungi, and protists.

Pathogen = Invader; Infected Organism = Host

Question 2

Archaea

Answer 2

Bacteria under this domain do not cause disease.

Question 3

Describe:

Skin as a Barrier

Answer 3

• Layer of dead cells, containing large amounts of keratin. Hard for pathogens to pass through.
• Sebaceous glands (related to hair follicles) which secrete the chemical sebum. Low pH inhibits bacteria and fungi growth.
• Mucous membranes secrete mucus—a sticky solution of glycoproteins (type of physical barrier). Pathogens and harmful particles get trapped in it, then swallowed or expelled. Additionally, it has antiseptic properties (due to the presence of antibacterial lysozyme).

Question 4

Describe:

Process of Clotting

Answer 4

1. Platelets (blood-cell fragments) aggregate at injured site, forming a temporary plug.
2. Platelets then release clotting factors which trigger clotting process.
3. Cascade of reactions, leading to production of thrombin (enzyme).
4. Thrombin converts fibrinogen (protein), which is dissolved in blood plasma, into insoluble fibrin.
5. Fibrin forms a mesh, trapping more platelets and blood cells.
6. Resulting clot is a gel, but dries when exposed to air—forming a hard scab.

Question 5

Describe:

Innate Immune System

Answer 5

• Responds to broad categories of pathogens.
• Does not change during organism’s life.
• Phagocytes a part of it.

Question 6

Describe:

Adaptive Immune System

Answer 6

• Responds in a specific way to particular pathogens.
• Builds up memory of encountered pathogens.
• Offers more effective protection against common infectious diseases.
• Lymphocytes (produce antibodies) a part of it.

Question 7

What happens if microorganisms get past skin and mucous membranes?

Phagocytes as Defense

Answer 7

• Phagocytes squeeze out pores in walls of capillaries and move to infection sites.
• There, they engulf pathogens through endocytosis and digest them using enzymes from lysosomes.
• Infected wounds attract large numbers of phagocytes, resulting in formation of white liquid (pus).

Type of white blood cell.

Question 8

Describe:

Lymphocytes

Answer 8

• Occur in large numbers in lymph nodes (swollen structures in lymphatic system).
• Produce antibodies, large proteins that help destroy pathogens. They have two function parts.
  1. Hypervariable region that recognizes and binds to a specific pathogen.
  2. Region that helps body fight the pathogen.
• Produce only one type of antibody.

Type of white blood cell.

Question 9

How do lymphocytes recognize pathogens?

Answer 9

Lymphocytes need to distinguish between body cells (“self-cells”) and “non-self” cells (such as pathogens). This is done via the molecule differences between pathogens and body cells.

Question 10

Antigen

Answer 10

Molecules used for recognition, usually located on surface of pathogen; Any molecule that stimulates an immune response.

Question 11

What do lymphocytes do in response to antigens?

Answer 11

• In response to antigen, lymphocytes produce antibodies, which bind to antigen.
• Protrusions on antigen match hollows on corresponding antibodies (also, positive match negative charges).
• Antibody to antigen binding is irreversible.
• One lymphocyte only produces antibodies with one type of hypervariable region (area that binds to antigen) and this only binds to specific antigens (‘specificity in binding’).

Question 12

How are helper T-cells activated?

Answer 12

1. Pathogens ingested by macrophages (type of phagocytic white blood cell).
2. Antigens from pathogen displayed in plasma membrane of macrophage.
3. Helper T-lymphocytes bind to antigen, as they have antibody-like receptor proteins in their plasma membrane.
4. Now activated, helper T-cells bind to B-lymphocytes (only B-cells with a specific receptor protein that antigen binds to are selected, then undergo binding process)
5. Helper T-cells activate selected B-cells, by means of both binding and release of signalling protein.

Question 13

How do B-cells multiply after activation?

Answer 13

When a pathogen first invades the body, development of immunity depends on the presence of B-lymphocytes capable of producing an effective antibody.
1. After becoming activated, B-cells don’t immediately produce antibodies, as: a) Too few B-cells to make significant quantity. b) Not yet have all organelles needed.
2. Consequently, activated B-cells divide repeatedly by mitosis to form clone cells (all produce same antibody).
3. These B-cells grow in size, forming needed organelles.
4. Result? Allows rapid production of antibodies by protein synthesis.

Question 14

Plasma B-Cells

Answer 14

Cells that have grown and differentiated for antibody production (“clones”).

Question 15

What happens to antibodies after infection?

Answer 15

Immunity: Ability to eliminate an infectious disease from the body.
* Antibodies do this, but only persist for few weeks or months after secretion in plasma B-cells.
* Gradually lost after infection is overcome (as antigens associated with infection no longer present).

Immunity to an infectious disease is due to having either antibodies against the pathogen, or memory cells that allow rapid production of the antibody

Question 16

What are memory B-cells?

Answer 16

• Most become active plasma B-cells.
• Do not survive long after fulfilling role of rapid antibody production.
• Small number do not immediately secrete antibodies, but remain long after infection.
• These ‘memory B-cells’ remain inactive, unless pathogen infects body again—in which they become activated and respond quickly.

Immunity to an infectious disease is due to having either antibodies against the pathogen, or memory cells that allow rapid production of the antibody