C3.2 Defense against disease

What is a pathogen?

Organisms that cause disease and are usually microorganisms.

What are the three main causes of disease identified by scientific research?

Genetic causes, environmental causes, and infection with a pathogen.

What is the difference between a pathogen and a parasite?

Pathogens are microorganisms that cause disease, while parasites are organisms that can be seen with the naked eye and often invade the body, causing harm.

What are the two domains of bacteria that exist?

Archaea and Eubacteria.

Why are viruses not usually considered to be alive?

They cannot reproduce on their own and need a host cell to replicate.

What is the primary defense against pathogens entering the body?

The skin, which acts as a physical barrier.

What does sebum do in the skin?

Sebum maintains skin moisture and lowers skin pH to inhibit the growth of bacteria and fungi.

What is the role of mucous membranes?

They secrete mucus, which traps pathogens and harmful particles and has antiseptic properties due to lysozyme.

What happens when the skin is cut?

Blood vessels are severed, and blood clots to seal the wound and prevent further blood loss and pathogen entry.

What is the process called that stops bleeding after a cut?

Clotting.

What triggers the clotting process?

Platelets, which aggregate at the site of injury and release clotting factors.

What is thrombin’s role in blood clotting?

Thrombin converts fibrinogen into insoluble fibrin, which forms a mesh to trap blood cells and platelets.

What is the difference between the innate and adaptive immune systems?

The innate immune system responds to broad categories of pathogens and does not change throughout life, while the adaptive immune system responds specifically to pathogens and builds memory.

What are phagocytes?

White blood cells that engulf and digest pathogens through endocytosis.

What is pus made of?

Pus is formed from a large number of phagocytes and dead pathogens at an infection site.

What are lymphocytes?

A type of white blood cell that plays a key role in the adaptive immune system by producing antibodies.

Where do lymphocytes occur?

Lymphocytes occur in the lymphatic system, particularly in lymph nodes.

What do antibodies do?

Antibodies recognize and bind to specific antigens on pathogens, helping the immune system fight the infection.

How do antibodies help in fighting pathogens?

They make pathogens more recognizable to phagocytes and prevent viruses from entering host cells.

Why can the adaptive immune system fight future infections more effectively?

It has memory of previously encountered pathogens, which helps in faster and stronger responses.

What is an antigen?

A molecule on a pathogen that triggers an immune response by stimulating antibody production.

How do lymphocytes recognize pathogens?

By detecting antigens on the surface of pathogens that are different from the body’s own cells.

What happens when a B-lymphocyte binds to an antigen?

It is activated, and its number increases by mitosis to produce antibodies.

What is the role of helper T-lymphocytes in the immune response?

They activate B-lymphocytes by binding to them and releasing signaling proteins.

What is the difference between plasma B-cells and memory B-cells?

Plasma B-cells produce large amounts of antibodies, while memory B-cells remain dormant and allow for rapid response in case of future infections by the same pathogen.

What is immunity?

The ability to resist an infection through the presence of antibodies or memory cells.

How does memory B-cell function contribute to immunity?

They remain inactive until the same pathogen infects the body again, at which point they rapidly produce antibodies.

What is HIV?

Human Immunodeficiency Virus, which causes Acquired Immunodeficiency Syndrome (AIDS).

How does HIV spread?

Through direct contact with infected body fluids, such as blood, semen, vaginal fluids, and breast milk.

What is the consequence of HIV infecting the immune system?

It destroys helper T-cells, impairing the body’s ability to produce antibodies and increasing susceptibility to opportunistic infections.

What are antiretroviral drugs used for?

They inhibit the reverse transcriptase enzyme of HIV, preventing the virus from replicating.

Why are antibiotics ineffective against viruses?

Viruses rely on the host cell's machinery to replicate, so antibiotics cannot target the virus without damaging the host cell.

What do antibiotics do?

Antibiotics inhibit the growth of bacteria by targeting processes like DNA replication, transcription, translation, and cell wall formation.

Why is antibiotic resistance a growing concern?

Bacteria evolve resistance mechanisms, making some antibiotics ineffective, and new antibiotics are not being discovered quickly enough.

What is methicillin-resistant Staphylococcus aureus (MRSA)?

A strain of bacteria resistant to many antibiotics, making it harder to treat infections.

What is multidrug-resistant tuberculosis (MDR-TB)?

A strain of tuberculosis resistant to multiple antibiotics, causing treatment challenges.

How can antibiotic resistance be prevented?

By limiting the use of antibiotics to serious bacterial infections, maintaining hygiene in hospitals, and avoiding the use of antibiotics in animal feed.

What is a zoonosis?

A disease that can be transmitted from animals to humans.

What is the origin of the COVID-19 virus?

It is thought to have originated in bats and possibly transmitted to humans via another animal species.

What is herd immunity?

When a significant proportion of a population is immune to a disease, reducing its spread.

What percentage of a population must be vaccinated to achieve herd immunity for measles?

93% of the population must be vaccinated.

What is a vaccine?

A substance that stimulates the immune system to produce a primary immune response and build immunity against a pathogen.

How do vaccines lead to immunity?

By introducing antigens that trigger the production of specific antibodies and memory cells.

What is the role of nucleic acids in some vaccines?

They allow the body to produce antigens, triggering an immune response.

What does the immune system do in response to a vaccine?

It activates T-lymphocytes and B-lymphocytes, leading to the production of plasma cells and antibodies.

What is herd protection?

The indirect protection from disease for vulnerable individuals because a significant portion of the population is immune.

What is the formula for calculating the percentage of people who need to be immune for herd immunity?

(1 - 1/R) × 100%, where R is the average number of people infected by one infected person.

What is the R value of measles?

15.

What is the benefit of herd immunity?

It reduces the spread of disease and protects vulnerable individuals who cannot be vaccinated.

How does immunity from a vaccine differ from immunity through infection?

Vaccine-induced immunity is often safer and avoids the risks associated with getting the disease.

What role does the lymphatic system play in immunity?

It helps transport lymphocytes and facilitates immune responses to pathogens.

What is the role of the spleen in immunity?

The spleen filters the blood and helps to remove pathogens and dead blood cells.

How do macrophages contribute to immunity?

They ingest pathogens and display their antigens to activate T-lymphocytes.

What are the components of blood that play a role in immune defense?

White blood cells (like phagocytes and lymphocytes), platelets, and plasma.

What is the role of the complement system?

It helps to destroy pathogens by promoting phagocytosis and damaging pathogen membranes.

What are the effects of inflammation during an infection?

It increases blood flow to the infected area, bringing more immune cells to fight the infection.

What is an autoimmune disease?

A disease where the immune system mistakenly attacks the body’s own cells.

What is the treatment for autoimmune diseases?

Treatment usually involves immunosuppressive drugs to reduce the immune response.

What is an example of an autoimmune disease?

Type 1 diabetes, where the immune system attacks insulin-producing cells in the pancreas.

What are the main functions of antibodies?

To neutralize pathogens, opsonize pathogens for phagocytosis, and activate the complement system.

What are B-cells responsible for?

Producing antibodies that help in the immune response to pathogens.

How do T-cells contribute to immunity?

They help activate other immune cells, such as B-cells and macrophages, and can directly kill infected cells.

What is an example of a bacterial infection that can be treated with antibiotics?

Pneumonia caused by bacteria.

How do antibiotics differ from antivirals?

Antibiotics target bacterial processes, while antivirals inhibit viral replication.

What is the role of antibiotics in preventing bacterial infections after surgery?

Antibiotics are used to prevent bacterial infections in patients who undergo surgery.

How does the immune system differentiate between “self” and “non-self” cells?

By recognizing antigens on the surface of cells that are different from the body’s own cells.

What is the function of plasma B-cells?

They produce large amounts of antibodies during an immune response.

What is a vaccination schedule?

A recommended timeline for receiving vaccines to ensure immunity against specific diseases.

How do vaccines prevent the spread of infectious diseases?

By reducing the number of people susceptible to infection, preventing outbreaks.