B13 entire unit

What is a pathogen?

A pathogen is a microorganism that causes disease in its host; Pathogens include bacteria, viruses, fungi, and protists;

Each pathogen has specific surface antigens that the immune system recognizes and responds to

What is a transmissible disease?

A transmissible disease is a disease that can spread from one host to another;

Transmission can occur through direct contact with an infected individual or indirectly via contaminated surfaces, air, food, or animals

What are the ways that pathogens are transmitted?

Pathogens can be transmitted by direct contact, including through bodily fluids such as blood, saliva, and sexual fluids; Indirect transmission occurs via contaminated surfaces, food, water, animals, or airborne particles such as droplets from coughs and sneezes

Why is a clean water supply important in controlling the spread of disease?

A clean water supply prevents the spread of waterborne diseases such as cholera and dysentery;

Contaminated water can carry bacteria, viruses, and parasites that cause illness when consumed;

Ensuring access to clean drinking water reduces infection rates in communities

How does hygienic food preparation help prevent disease?

Proper food handling reduces contamination with harmful bacteria such as Salmonella and E. coli;

Cooking food at high temperatures kills pathogens, preventing foodborne illnesses;

Storing food at appropriate temperatures slows bacterial growth and reduces spoilage

What are the benefits of good personal hygiene in disease prevention?

Washing hands with soap removes pathogens that could be transmitted to the mouth, nose, or eyes;

Covering coughs and sneezes prevents airborne spread of pathogens;

Regular bathing reduces the accumulation of bacteria and fungi on the skin

How does waste disposal contribute to disease control?

Proper waste disposal limits exposure to disease-carrying vectors such as rats, flies, and mosquitoes;

Waste can contain harmful bacteria, viruses, or toxins that may spread if not disposed of safely;

Reducing waste accumulation helps prevent outbreaks of infectious diseases

How does sewage treatment help prevent disease transmission?

Sewage treatment removes harmful pathogens from human waste before it enters water sources;

Without treatment, contaminated water can cause outbreaks of diseases like cholera and typhoid;

Properly treated sewage prevents environmental pollution and improves public health

What are the three lines of defence in the immune system?

The body's defences consist of three lines of defence that protect against pathogens;

The first line consists of physical and chemical barriers that prevent pathogen entry;

The second line involves non-specific phagocytosis by white blood cells;

The third line includes the specific immune response, which involves antibody production

What is included in the first line of defence?

The first line of defence consists of physical and chemical barriers that prevent pathogens from entering the body;

The skin acts as a physical barrier and secretes antimicrobial substances;

Hairs in the nose trap pathogens, preventing them from entering the respiratory system;

Mucus in the respiratory tract traps pathogens, which are then removed by cilia;

Stomach acid kills pathogens that are ingested with food or water

What happens in the second line of defence?

The second line of defence is a non-specific immune response that involves phagocytosis;

Phagocytes engulf and digest pathogens using enzymes in lysosomes;

Phagocytes also present antigens to activate the specific immune response

What is the role of the third line of defence?

The third line of defence is the specific immune response, which targets specific pathogens;

lymphocytes recognise antigens and produce antibodies to neutralise them;

Why does each pathogen trigger a unique immune response?

Each pathogen has its own specific antigens, which act as molecular markers;

The immune system recognises these antigens and produces antibodies that match their shape;

This ensures a targeted and effective immune response against different pathogens

What are antibodies and how do they function?

Antibodies are specialised proteins produced by B-lymphocytes in response to infection;

They bind to antigens on pathogens, neutralising them directly or preventing them from entering host cells;

Antibodies also tag pathogens for destruction by phagocytes, enhancing immune response efficiency

Why do antibodies only bind to specific antigens?

Antibodies have a unique structure with antigen-binding sites that are complementary in shape to a specific antigen;

This ensures that the immune system targets only the correct pathogen without affecting the body's own cells

What are the stages of antibody production?

The immune system first detects foreign antigens on the surface of pathogens;

lymphocytes recognise these antigens and become activated; Activated lymphocytes undergo divide rapidly by mitosis to produce plasma cells;

Plasma cells secrete large quantities of antibodies that bind to and neutralise the pathogen;

Memory lymphocytes remain in the bloodstream, providing long-term immunity by enabling a faster immune response upon re-exposure to the same pathogen

What is active immunity?

Active immunity is gained after infection by a pathogen or through vaccination;

It involves the production of memory cells, providing long-term protection against disease

How does vaccination provide immunity?

Vaccination introduces weakened pathogens or their antigens into the body;

These antigens stimulate an immune response, causing lymphocytes to produce antibodies;

Memory cells are formed, providing long-term immunity against the disease

Why are memory cells not produced in passive immunity?

Passive immunity occurs when antibodies are directly transferred into the body, rather than produced by lymphocytes;

Since no immune response occurs, no memory cells are formed, and immunity is short-term

How do vaccination programmes help control disease spread?

Vaccination reduces the number of susceptible individuals in a population, lowering disease transmission;

Herd immunity (the immunity of the many) protects those who cannot be vaccinated, helping to eradicate diseases such as smallpox;

Why are viruses not considered living organisms?

Viruses do not carry out metabolism, cannot reproduce independently, and lack cellular structures;

They require a host cell to replicate and perform life functions, meaning they do not meet all criteria for life;

they have no metabolism of their own;

Why do viruses rely on a host cell?

Viruses cannot metabolise, synthesize proteins, or reproduce on their own;

They hijack the host cell's machinery to produce viral proteins, replicate genetic material, and assemble new viruses

How can viruses infect multiple species? How do they transfer from species to species and what is this known as?

Some viruses are species-specific and only infect certain organisms;

Others, like influenza and coronaviruses, can cross species barriers, leading to zoonotic infections; this happens when mutations occur;

this is called zoonosis;

What is a sexually transmitted infection (STI)?

An STI is an infection that is transmitted through sexual contact, including vaginal, oral, or anal sex;

Some STIs, such as HIV, can also be transmitted through blood or from mother to child during birth

What is HIV?

HIV (human immunodeficiency virus) is a virus that attacks the immune system and is transmitted primarily through sexual contact; It can weaken the immune response, making the body vulnerable to infections and diseases

How can HIV lead to AIDS?

HIV destroys lymphocyte cells, (specifically T-helper cells); weakening the body's ability to fight infections;

When the immune system is severely compromised, the individual develops AIDS (acquired immunodeficiency syndrome), leading to life-threatening infections

How is HIV transmitted?

HIV is transmitted through contact with infected bodily fluids, including blood, semen, vaginal fluids, and breast milk; Transmission can occur through unprotected sex, shared needles, from mother to baby during childbirth, or via contaminated blood transfusions

How can the spread of STIs be controlled?

Using barrier protection (e.g., condoms) during sexual activity reduces STI transmission;

Regular screening and early treatment help prevent further spread;

Public health campaigns and education promote awareness and safe practices

What is a drug?

A drug is any substance taken into the body that modifies or affects chemical reactions;

Drugs can have therapeutic effects (e.g., pain relief, antibiotics) or alter bodily functions (e.g., stimulants, depressants)

How do antibiotics treat bacterial infections?

Antibiotics kill or inhibit the growth of bacteria by targeting bacterial structures, such as cell walls or protein synthesis machinery;

They are effective against bacterial infections but have no effect on viruses

Why are some bacteria resistant to antibiotics?

Some bacteria have evolved resistance through genetic mutations or by acquiring resistance genes from other bacteria;

This reduces the effectiveness of antibiotics, making infections harder to treat

How can the development of antibiotic resistance be limited?

Antibiotics should only be used when necessary to reduce selective pressure on bacteria;

Completing the full course of prescribed antibiotics ensures that all bacteria, including partially resistant ones, are eliminated;

Public health strategies aim to control the spread of resistant bacteria such as MRSA

Why do antibiotics not work against viruses?

Viruses lack the structures that antibiotics target, such as cell walls and ribosomes;

Since viruses replicate inside host cells, antibiotics cannot interfere with their life cycle

How can bacterial growth be investigated in microbiology?

Bacteria can be cultured on agar plates to observe growth patterns;

The effectiveness of antimicrobial substances, such as ethanol, can be tested by applying different concentrations to bacterial cultures;

the zone where no growth is present, the zone of inhibition can be measured to assess effectiveness;

A control group using water ensures that changes in bacterial growth are due to the anti-microbial and not external factors;