Biology — The Immune System

What is a pathogen?

a disease-causing organism, such as a bacterium, virus, fungus, or protist

What is an antigen?

a molecule that triggers an immune response, usually found on a pathogen's surface

What is an antibody?

a Y-shaped protein that tags antigens for destruction

How do pathogens commonly spread?

through coughing, sneezing, physical contact, contaminated water, and body fluids

What is the innate immune system?

the non-specific defence that guards against all infection rather than one pathogen

What is the body's first line of defence?

the skin, which acts as a physical barrier

How are openings like the eyes and mouth protected?

by saliva, mucus, and tears, which carry an enzyme that breaks down bacterial cell walls

What is the inflammatory response?

increased blood flow lets phagocytes leave the vessels to engulf pathogens, making the area red, swollen, and sore

What are phagocytes?

white blood cells that engulf and destroy pathogens

Why does the body produce a fever?

a higher temperature slows pathogen growth and speeds up the immune response

What is the adaptive immune system?

the specific defence that targets a particular pathogen and remembers it

How does the immune system avoid attacking your own cells?

body cells carry self markers that identify them as self

What triggers a specific immune response?

antigens, which are unique to each pathogen

What are the two main immune cell types?

B cells and T cells, which are both a kind of lymphocyte

Where do B cells and T cells mature?

B cells mature in the bone marrow, while T cells mature in the thymus

What is humoral immunity?

adaptive defence that relies on antibodies circulating in the body

How does humoral immunity work?

a B cell binds an antigen and presents it to a helper T cell, which activates the B cell

What do activated B cells produce?

plasma cells that release antibodies, and memory B cells that store information for future immunity

What is cell-mediated immunity?

adaptive defence where T cells destroy infected body cells

What do killer T cells do?

release toxins into infected cells and trigger their death by apoptosis

What do helper T cells do?

activate other immune cells

What is the difference between humoral and cell-mediated immunity?

humoral uses antibodies from B cells, while cell-mediated uses T cells to kill infected cells

How do vaccines work?

they contain a pathogen's antigens, priming the body to make antibodies so it can fight that pathogen later

What is a virus?

a non-living infectious particle that hijacks a host cell to reproduce

What is a capsid?

the protective protein shell that houses a virus's genome

What does a virus's genome consist of?

nucleic acid, either DNA or RNA

What is a viral envelope?

a membrane layer that surrounds the capsid in some viruses

What are the five steps of viral infection?

attachment, entry, replication and gene expression, assembly, and release

What happens in the release step of viral infection?

the cell bursts (lyses), freeing new viral particles to infect other cells

Are all bacteria pathogens?

no, most are harmless or helpful, aiding digestion and making vitamins

Should we stop vaccinating for diseases that are now rare?

no, they still exist and could return without continued vaccination

Do vaccines always give permanent immunity?

no, some need repeating, like the flu shot which changes yearly as the virus mutates