VCE Biology 2026 Unit 4 AOS 1 - Pathogens and Immunity

These flashcards cover the essentials of VCE Biology Unit 4 AOS 1, including pathogen types, transmission, innate and adaptive immunity, vaccination strategies, immunotherapy, and bioethics.

How does the transcript defines a pathogen?

A disease causing agent that invades a host. Pathogens are either cellular (bacteria, fungi, protozoa and parasitic worms) or non cellular (viruses, viroids and prions).

What is the difference between infection and disease?

Infection is the invasion and multiplication of a pathogen within a host, whereas disease occurs when an infection damages the normal functioning or vital systems of the host.

How do non cellular pathogens differ from cellular pathogens in terms of replication?

Non cellular pathogens (viruses, viroids, and prions) have no metabolism of their own and replicate only by using a host cell, whereas cellular pathogens have their own metabolism and reproduce independently.

What are prions and how do they cause disease?

Infectious misfolded proteins with no nucleic acid. They cause disease by forcing normal prion proteins to refold into the misfolded, deadly shape; they act slowly and resist normal cooking temperatures.

What are the structural features of a virus?

A protein coat (capsid) around a core of either DNA or RNA (single or double stranded, never both). Enveloped viruses have an outer membrane with viral glycoproteins, while naked viruses lack this.

What characterizes bacteria as prokaryotic pathogens?

Genetic material is not enclosed in a nucleus; they have a peptidoglycan cell wall and may contain plasmids, flagella, a capsule to increase virulence, or resistant endospores.

List the six links in the chain of infection.

An infectious agent, a reservoir, a portal of exit, a mode of transmission, a portal of entry, and a susceptible host.

Distinguish between direct and indirect modes of transmission.

Direct modes include direct contact and droplet borne transmission. Indirect modes include airborne, vehicle borne (contaminated food/water/fomites), and vector borne transmission.

What are allergens?

Normally harmless environmental antigens that trigger an exaggerated immune response in sensitised individuals.

Contrast the innate and adaptive immune systems regarding speed and memory.

Innate immunity is fast with no lag phase but has no immunological memory. Adaptive immunity is slower on first exposure but has memory that improves with repeat exposure.

What are the first line physical barriers in animals?

Intact skin, mucous membranes, mucus, cilia and nasal hairs.

What is the role of the lymphatic system in the immune response?

It acts as a transport network for lymph and immune cells, and carries antigens to lymph nodes where immune responses are initiated by T and B lymphocytes.

Compare the functions of MHC class I and MHC class II molecules.

MHC class I is found on all nucleated body cells and presents antigens to cytotoxic T cells. MHC class II is found only on antigen presenting cells and presented to helper T cells.

What is the primary function of Dendritic cells?

They are the main antigen presenting cells that phagocytose pathogens and display antigen on MHC class II to activate helper T cells, bridging innate and adaptive immunity.

How do Natural Killer (NK) cells decide which cells to destroy?

They read MHC class I as a "do not kill" signal. They release perforin and granzymes to induce apoptosis in cells that lack MHC class I, such as some cancer or virus-infected cells.

What are the four outcomes of complement protein activation?

Opsonisation of pathogens, attraction of phagocytes by chemotaxis, formation of a membrane attack complex to lyse cells, and promotion of inflammation.

What are the five steps of the inflammatory response?

1. Mast cells release histamine causing vasodilation and leaky capillaries. 2. Phagocytes are attracted by chemotaxis. 3. Phagocytes destroy pathogens. 4. Macrophages clear debris and release cytokines. 5. Clotting seals the wound.

How do antibodies inactivate antigens through agglutination?

By cross linking pathogens into clumps, making them easier for the immune system to process.

Match the antibody classes IgE and IgM to their specific roles.

IgE protects against parasitic worms and drives allergic reactions; IgM is the first antibody made and is predominant in the primary response.

What occurs during clonal selection in the adaptive immune response?

A lymphocyte with a uniquely specific receptor matching a encountered antigen is selected and stimulated to divide (clonal expansion) in the lymph nodes.

Differentiate between natural active immunity and artificial passive immunity.

Natural active immunity is the production of antibodies/memory cells after a natural infection. Artificial passive immunity is receiving transitionally immediate protection via injected antibodies (e.g., antivenom).

How does a vaccine provide protection?

It introduces a weakened or partial pathogen to trigger a primary response and memory cell formation without causing disease, allowing for a rapid secondary response on later exposure.

Explain the concept of herd immunity.

When a high enough proportion of a population is immune (usually through vaccination), a contagious disease cannot spread easily, indirectly protecting those who cannot be vaccinated.

Describe the hybridoma technique for creating monoclonal antibodies.

An animal is injected with antigen to produce plasma cells, which are fused with myeloma (tumour) cells to form hybridomas that divide indefinitely and produce large quantities of specific antibodies.

Define the two stages of an allergic reaction.

Sensitisation (first exposure) where IgE attaches to mast cells, and Allergic reaction (later exposure) where the allergen cross-links IgE, triggering mast cell degranulation and histamine release.

What is the difference between antigenic drift and antigenic shift in viruses?

Antigenic drift involves gradual, small changes from point mutations. Antigenic shift is a sudden, major change often occurring when a virus recombines with an animal/avian strain.

Identify the five ethical concepts used in bioethical analysis.

Integrity, Justice, Beneficence, Non-maleficence, and Respect.

Contrast the Consequences-based and Duty-based approaches to bioethics.

A consequences-based approach aims to maximize positive outcomes (the ends), while a duty-based approach focuses on following specific rules or obligations (the means) regardless of the results.

What is the role of the cytotoxic T cells in the immune response?

Cytotoxic T cells, also known as CD8 cells, identify and destroy cells infected with pathogens or cancerous cells by recognizing antigens presented by MHC class I molecules.

How do antibodies neutralize toxins?

Antibodies neutralize toxins by binding to them and blocking their ability to interact with host cells, preventing the toxic effects.

What is the significance of memory T cells in adaptive immunity?

Memory T cells provide a faster and more robust response upon re-exposure to the same antigen, thereby enhancing the efficiency of the adaptive immune response.

How does the complement system enhance the immune response?

The complement system enhances the immune response by labeling pathogens for destruction (opsonization), attracting immune cells (chemotaxis), and directly lysing pathogen cells through the membrane attack complex.

What mechanisms do pathogens use to evade the immune system?

Pathogens employ mechanisms such as antigenic variation, hiding within host cells, and producing substances that suppress immune functions.

What is the difference between passive immunity and active immunity?

Passive immunity is the transfer of antibodies from one individual to another (e.g., from mother to child), while active immunity is the production of antibodies by the individual’s own immune system after exposure to an antigen.

Explain the role of interferons in the immune response.

Interferons are signaling proteins produced by virus-infected cells that help to inhibit viral replication and activate immune cells such as macrophages and natural killer cells.

What are superantigens, and how do they affect the immune response?

Superantigens are a class of antigens that cause excessive activation of the immune system by simultaneously binding to T-cell receptors and MHC class II molecules, leading to a massive cytokine release.

How do vaccines mimic natural infection?

Vaccines mimic natural infection by introducing harmless components of a pathogen (like antigens) to stimulate the immune system to produce antibodies and memory cells without causing disease.

What is the role of granulocytes in the immune system?

Granulocytes, including neutrophils, eosinophils, and basophils, are white blood cells that play key roles in inflammation and combatting infections, particularly parasitic infections and allergic reactions.