Antigens, Pathogens & Allergens – Lesson 16 Review

50 question-and-answer flashcards covering immune system basics, antigen recognition, MHC classes, blood cells, allergens, allergic responses, pathogen classification, viral and prion biology, bacterial virulence, fungal and protozoan infections, and key exam tips for VCE Biology Unit 4, AOS 1.

What is the primary function of the immune system?

To protect the body against invading agents such as viruses, bacteria and other foreign bodies.

What is an antigen?

A molecule (or part of one) that stimulates an immune response through antibody production.

What is the difference between self-antigens and non-self antigens?

Self-antigens originate within the host’s own body, whereas non-self antigens are foreign substances not normally present in the body.

What is immunological tolerance?

The immune system’s ability to avoid responding to self-antigens, preventing autoimmunity.

Name the two classes of MHC molecules.

MHC class I and MHC class II.

On which cells are MHC I molecules found?

All nucleated cells (and platelets) in the body.

Which cells present antigens via MHC II?

Professional antigen-presenting cells such as dendritic cells, macrophages and B cells.

What type of pathogens are primarily targeted by MHC I presentation?

Intracellular agents (e.g., viruses) presented to cytotoxic T cells.

List the four major components of blood.

Red blood cells, white blood cells, platelets and plasma.

Which layer in a centrifuged blood sample contains white blood cells and platelets?

The buffy coat.

What is another term for white blood cells?

Leukocytes.

Name the three main lymphocyte subtypes.

B cells, T cells and natural killer (NK) cells.

Which white blood cells are most abundant in human blood?

Neutrophils (≈50-70 % of WBCs).

Which WBC is most effective against parasitic worms?

Eosinophils.

Which granulocyte mediates allergic responses in the bloodstream?

Basophils.

What chemical mediator released from mast cells and basophils causes allergy symptoms?

Histamine.

Define allergen.

Any antigen that triggers an abnormally heightened (hypersensitive) immune response.

Outline the three key steps in the simple model answer for an allergic response.

1) Identify the allergen; 2) Allergen binds to and activates mast cells; 3) Degranulation releases histamine, causing allergic symptoms.

Differentiate cellular and non-cellular pathogens and give one example of each.

Cellular pathogens are living cells (e.g., bacteria); non-cellular pathogens lack cellular structure and life processes (e.g., viruses or prions).

What is a virion?

An inactive viral particle existing outside a host cell that facilitates viral transfer between hosts.

How do viruses differ from prions in genetic content?

Viruses contain DNA or RNA; prions contain no nucleic acids—only protein.

Define an obligate intracellular pathogen and name one.

A pathogen that can replicate only inside a host cell; example: a virus (e.g., influenza virus).

What two structural components make up a viral nucleocapsid?

The viral genetic material (DNA or RNA) and the surrounding protein capsid.

Why are enveloped viruses generally easier to destroy with detergents than naked viruses?

Their lipid envelope is sensitive to heat, drying, acids and detergents, which disrupt the membrane and inactivate the virus.

What type of genetic material does the influenza virus contain?

Single-stranded RNA (ssRNA).

Which virus causes chickenpox?

Varicella-zoster virus (VZV).

What protein-only pathogen causes Creutzfeldt-Jakob Disease?

A prion (PrP^Sc).

How do prions convert normal proteins into infectious forms?

Contact with a misfolded prion induces conformational change in normal proteins, converting them into the pathogenic form.

What bacterial reproduction process divides one cell into two identical daughter cells?

Binary fission.

List the four ordered steps of binary fission.

1) Parent cell initiates DNA replication; 2) Cell elongates and forms a cross wall; 3) A copy of parental DNA moves to each side; 4) Daughter cells separate at the cross wall.

Give one virulence factor used by Salmonella species.

Flagella for motility (others include capsule and adhesive systems).

Which bacterium causes tetanus and what is the main toxin’s effect?

Clostridium tetani; its neurotoxin blocks muscle relaxation, causing rigid spasms.

Name the bacterial pathogen responsible for bubonic plague.

Yersinia pestis.

What is an opportunistic pathogen?

An organism that normally does not cause disease but can do so under specific conditions, such as a weakened immune system.

How do fungi typically reproduce?

By spreading microscopic spores.

What term describes the filament structures of fungi?

Hyphae (collectively forming mycelia).

Provide one common transmission route for histoplasmosis.

Inhalation of soil spores, especially from areas with bat or bird droppings.

Which fungal species commonly causes thrush?

Candida albicans.

Define protozoa.

Single-celled eukaryotic organisms that may be free-living or parasitic.

What is the dormant, infective life stage of many protozoa called?

A cyst.

Which protozoan parasite causes amoebic dysentery?

Entamoeba histolytica.

How is Cryptosporidium parvum commonly transmitted to humans?

Via the faecal-oral route, often through ingestion of contaminated water or direct contact with infected animal faeces.

Describe the general model framework for answering pathogen disease-related questions.

State the pathogen, list its virulence factor(s), explain how those factors work, and detail the specific impact on the host.

What percentage of white blood cells do neutrophils normally represent?

Approximately 50–70 % of total WBCs.

Which cells are functionally similar to basophils but reside in tissues?

Mast cells.

Give two factors that can suppress the immune system and increase infection risk.

Stress, sleep deprivation, poor nutrition, or chemotherapy (any two).

Why must the body distinguish self from non-self antigens?

To prevent the immune system from attacking the body’s own tissues and causing autoimmune disease.

What is meant by an endogenous antigen?

An antigen that originates from within the body, such as on cancer cells or virus-infected cells.

What does HLA stand for?

Human Leukocyte Antigen (the human form of MHC).