COMMUNICABLE DISEASES & PATHOGENS

What is a pathogen?

A microorganism that causes disease.

What is a communicable disease?

A disease that can spread between organisms.

What are the four main types of pathogen?

Bacteria, viruses, fungi and protists.

How do bacteria cause disease?

They reproduce rapidly and can release toxins that damage tissues.

How do viruses cause disease?

They reproduce inside host cells, damaging or destroying the cells.

How do fungi cause disease?

They may grow on host surfaces and produce spores that spread.

How do protists cause disease?

They are eukaryotic parasites that live in or on hosts and cause damage.

What is a vector?

An organism that transfers a pathogen between hosts without being affected by it.

Give four ways communicable diseases can spread.

Air/droplets, direct contact, contaminated food or water, and vectors

How can contaminated food or water spread disease?

People ingest pathogens in the contaminated food or water.

How can airborne diseases be spread?

Pathogens travel in droplets released by coughing or sneezing, which others inhale.

How can people reduce disease spread through food?

Wash hands before preparing food, clean surfaces and cook food thoroughly.

How can people reduce the spread of airborne diseases?

Cover coughs and sneezes, maintain hygiene and isolate infected people when appropriate.

How can vector-borne disease transmission be reduced?

Use insecticides and mosquito nets, and remove stagnant water where mosquitoes breed.

How can plant pathogens spread?

Direct contact, wind, water, insect vectors, soil and contaminated tools or hands.

How can farmers reduce the spread of plant diseases?

Remove/burn infected plants, sterilise tools, control vectors, rotate crops and grow resistant varieties.

What causes measles, and how does it spread?

A virus; it spreads through droplets from coughs and sneezes.

What are the symptoms and risks of measles?

Fever and a red skin rash; serious complications can include brain damage or death.

How can measles be prevented or controlled?

Vaccination and isolating infected people to reduce transmission

How is HIV transmitted?

Through infected body fluids, including during sexual contact, sharing needles or blood exposure.

What does HIV do to the body?

It attacks white blood cells, weakening the immune system; untreated infection can lead to AIDS.

How can HIV transmission be reduced?

Use condoms/barrier contraception and avoid sharing needles.

How can HIV infection be treated?

Antiretroviral drugs reduce viral replication and help prevent progression to AIDS.

What is TMV?

Tobacco Mosaic Virus, a plant virus that causes a mosaic pattern of leaf discolouration.

How does TMV affect plants?

It reduces chlorophyll and photosynthesis, so less glucose is available for growth.

How does TMV spread?

Through contact between infected and healthy plants, or contaminated hands and tools.

How can TMV be controlled?

Remove and destroy infected plants and sterilise tools.

Exam: Explain how TMV reduces plant growth (3 marks).

TMV reduces chlorophyll; less light is absorbed, reducing photosynthesis and glucose production, so less is available for growth.

What causes salmonella, and how does it spread?

Salmonella bacteria; it spreads through contaminated food and unhygienic food preparation.

What are the symptoms of salmonella food poisoning?

Fever, stomach cramps, vomiting and diarrhoea.

What causes the symptoms of salmonella?

Toxins produced by the bacteria.

How can salmonella be treated and prevented?

Antibiotics may treat it; hygienic food preparation, handwashing and thorough cooking help prevent it.

How is salmonella controlled in UK poultry?

Chickens are vaccinated to reduce salmonella infections.

How can someone with salmonella reduce its spread?

Wash hands thoroughly after using the toilet and after vomiting, and maintain good hygiene.

What causes gonorrhoea, and how does it spread?

A bacterium spread through sexual contact.

What are the symptoms of gonorrhoea?

Yellow or green discharge and pain when urinating.

How is gonorrhoea treated and prevented?

Antibiotics treat it, although resistant strains exist; condoms and early diagnosis help control spread.

What is antibiotic resistance?

When bacteria are no longer killed by a particular antibiotic.

Why is MRSA difficult to treat?

It has evolved resistance to many antibiotics.

Exam: What causes vomiting and diarrhoea in salmonella infection?

Toxins produced by the salmonella bacteria.

Exam: Give one way an infected person can reduce salmonella spread.

Wash hands thoroughly after using the toilet.

Cook food properly

What causes athlete's foot, and how does it spread?

A fungus spread through skin contact or contaminated surfaces, towels and footwear.

What are the symptoms of athlete's foot?

Itchy, red, flaky, cracked or peeling skin, often between the toes.

How is athlete's foot treated and prevented?

Use antifungal treatment; keep feet clean and dry, wear flip-flops in communal showers and do not share towels or shoes.

What causes rose black spot, and how does it spread?

A fungus spread by wind, water/rain splash and contaminated tools or insects.

How does rose black spot affect plants?

Dark leaf spots develop; leaves yellow and drop early, reducing photosynthesis and growth.

How can rose black spot be controlled?

Use fungicides and remove/destroy infected leaves; avoid overhead watering and overcrowding.

What is a fungicide?

A substance that kills fungi or stops their growth.

What causes malaria, and how is it transmitted?

Plasmodium, a protist, is transmitted by the bite of an infected female mosquito.

What are the symptoms and risks of malaria?

Repeated episodes of fever; severe malaria can be fatal if untreated.

How can malaria transmission be reduced?

Mosquito nets, insecticides, repellents, covering skin and removing stagnant water.

How can malaria transmission be reduced?

Mosquito nets, insecticides, repellents, covering skin and removing stagnant water.

How can malaria be treated?

Antimalarial drugs, although resistant strains can develop.

Why are mosquitoes called vectors in malaria transmission?

They transfer the Plasmodium protist between hosts.

Exam: Why can releasing sterile male mosquitoes reduce malaria?

Fewer successful matings produce fewer offspring, reducing mosquito numbers and therefore transmission of the protist.

What are non-specific defences?

Defences that act against a wide range of pathogens, rather than one specific pathogen.

How does the skin protect the body?

It acts as a physical barrier that prevents pathogens entering.

How do nose hairs and mucus protect the body?

They trap pathogens in inhaled air.

What do goblet cells do?

They produce mucus that traps pathogens.

What do ciliated cells do in the airways?

Their cilia move mucus containing trapped pathogens towards the throat.

What happens to mucus and trapped pathogens moved to the throat?

They are swallowed and stomach hydrochloric acid can kill the pathogens.

How does hydrochloric acid in the stomach protect the body?

It kills many pathogens that have been swallowed.

How do platelets help protect the body?

They help blood clot at a wound, forming a scab that restores the barrier.

Exam: Give two ways the body prevents pathogens entering (2 marks).

Any two: skin acts as a barrier; mucus traps pathogens; cilia move mucus to the throat; stomach acid kills swallowed pathogens.

Exam: Describe how the body prevents entry and defends against pathogens (6 marks).

Skin forms a barrier; mucus traps pathogens; cilia move mucus to the throat to be swallowed; stomach acid kills pathogens; phagocytes engulf and digest pathogens; lymphocytes make specific antibodies.

What is the role of white blood cells?

They defend the body against pathogens.

What is phagocytosis?

The process where a phagocyte engulfs and digests a pathogen.

Describe phagocytosis.

A phagocyte surrounds and engulfs the pathogen, then enzymes digest it inside a vacuole.

What is an antigen?

A molecule, often a surface protein, recognised by the immune system as a marker on a cell or pathogen.

What is an antibody?

A protein made by lymphocytes that binds to a specific complementary antigen.

Why are antibodies specific?

Their binding sites are complementary to particular antigens.

What are memory cells?

Cells that remain after an infection and enable a faster response if the same pathogen returns.

What happens when the same pathogen infects the body again?

Memory cells rapidly produce large amounts of the correct antibodies, often destroying the pathogen before symptoms develop.

What are antitoxins?

Substances produced by white blood cells that neutralise toxins made by bacteria.

What is the difference between phagocytosis and antibody production?

Phagocytosis is non-specific; antibody production targets specific antigens.

What is the difference between antibodies and antibiotics?

Antibodies are immune proteins that bind specific antigens; antibiotics are medicines that kill bacteria or stop them reproducing.

Exam: Describe how the immune system defends against pathogens (4 marks).

Phagocytes engulf and digest pathogens; lymphocytes produce antibodies specific to antigens; antitoxins neutralise bacterial toxins; memory cells enable a faster response on reinfection.

What does a vaccine contain?

Antigens from a pathogen, often supplied using weakened or inactivated pathogens or other vaccine technology.

How does vaccination stimulate immunity?

Vaccine antigens stimulate white blood cells to produce specific antibodies and memory cells.

Describe how vaccination protects against future infection.

Memory cells recognise the same antigens later and rapidly produce large quantities of antibodies, destroying the pathogen before illness develops.

What is herd immunity?

When high vaccination coverage reduces disease transmission, helping protect people who cannot be vaccinated.

Give two benefits of vaccination.

It prevents serious disease and reduces spread; vaccination has helped eradicate smallpox.

Give two possible limitations or challenges of vaccination.

Mild side effects such as fever or swelling, needle fear, the need for boosters, or reduced uptake due to misinformation.

Why might booster vaccinations be needed?

Protection can decrease over time, so another dose may be needed to maintain immunity.

Exam: Describe how a new gonorrhoea vaccine could work (4 marks).

Vaccine antigens stimulate white blood cells to produce specific antibodies; some become memory cells; on later exposure, memory cells rapidly produce antibodies; antibodies help destroy the pathogen.

Exam: Give the correct sequence for vaccination.

Vaccine antigens → white blood cells respond → specific antibodies produced → memory cells remain → faster antibody production on re-exposure.

Why do vaccines not always prevent every infection?

Protection varies by vaccine and pathogen; immunity may be incomplete or wane, and some pathogens change their antigens.

What are antibiotics?

Medicines that kill bacteria or stop them reproducing.

Why don't antibiotics work against viruses?

Viruses reproduce inside host cells and lack the bacterial structures targeted by antibiotics.

Who discovered penicillin, and where did it come from?

Alexander Fleming discovered penicillin from Penicillium mould.

Why are antibiotics important?

They reduce deaths from bacterial diseases, prevent serious complications and help make surgery and some cancer treatments safer.

How can antibiotic misuse cause resistance?

Resistant bacteria survive treatment and reproduce, making resistant strains more common.

What is MRSA?

A strain of bacteria resistant to several antibiotics, making infections difficult to treat.

What are painkillers, and what do they do?

Medicines such as paracetamol and ibuprofen that relieve symptoms like pain or fever.

Do painkillers kill pathogens?

No. They relieve symptoms while the immune system fights the infection.

Exam: Explain why antibiotics cannot treat measles (3 marks).

Measles is caused by a virus. Viruses reproduce inside host cells. Antibiotics target bacteria, not viruses.

What is the key difference between antibiotics and painkillers?

Antibiotics act against bacteria; painkillers relieve symptoms but do not kill pathogens.

Where does digitalis come from, and what is it used for?

Foxgloves; it is used to treat certain heart conditions.

Where does aspirin come from?

Willow bark; aspirin is a painkiller.

Where does penicillin come from?

Penicillium mould; it is an antibiotic.