B4.3. Infection and Response

What is a pathogen?

A microorganism that causes disease.

What are the four main types of pathogen?

Viruses, bacteria, fungi and protists.

What is a communicable disease?

A disease that can be spread from one organism to another.

How can pathogens spread between people?

Through air, direct contact, contaminated food or water, and body fluids.

How can pathogens spread through the air?

Pathogens can be carried in droplets released when an infected person coughs or sneezes.

How can pathogens spread through direct contact?

Pathogens can be transferred when an infected person comes into physical contact with another person.

How can pathogens spread through contaminated food or water?

Pathogens can enter the body when contaminated food or water is consumed.

How can pathogens spread through body fluids?

Pathogens can be transferred through fluids such as blood or sexual fluids.

What is a virus?

A pathogen that reproduces inside living cells.

Why do viruses cause damage to cells?

They reproduce inside cells and can damage or destroy the cells.

What is a bacterium?

A single-celled microorganism that can reproduce rapidly inside the body.

How can bacteria cause disease?

They can reproduce inside the body and produce toxins that damage cells and tissues.

What is a fungus?

A microorganism that can cause disease and often grows as thread-like structures called hyphae.

What is a protist?

A single-celled eukaryotic organism. Some protists are pathogens.

How can protists be transmitted?

Some are transmitted by vectors such as mosquitoes.

What is a vector?

An organism that carries and transmits a pathogen without necessarily being affected by the disease itself.

What is malaria?

A communicable disease caused by a protist pathogen and spread by mosquitoes.

How can the spread of malaria be reduced?

By controlling mosquito populations and preventing mosquito bites, for example using insecticide-treated bed nets.

What is a bacterial disease example you need to know?

Salmonella.

How is Salmonella spread?

Through contaminated food.

What symptoms can Salmonella cause?

Fever, stomach cramps, vomiting and diarrhoea.

How can Salmonella infections be reduced?

By maintaining good food hygiene and controlling the temperature at which food is stored and cooked.

What is a viral disease example you need to know in humans?

Measles.

How is measles spread?

Through droplets from coughs and sneezes.

How can measles spread be reduced?

By vaccination.

What is HIV?

A virus that attacks the immune system.

How is HIV spread?

Through body fluids such as blood and sexual fluids.

What can happen if HIV is untreated?

It can damage the immune system and may eventually lead to AIDS.

What is AIDS?

A condition in which the immune system has been severely damaged by HIV.

How can HIV be controlled?

Using antiretroviral drugs that reduce the amount of virus in the body.

What is tobacco mosaic virus?

A viral disease of plants.

What symptoms can tobacco mosaic virus cause?

It causes a mosaic pattern of discolouration on leaves.

How does tobacco mosaic virus affect plants?

The discolouration reduces the amount of chlorophyll available for photosynthesis, reducing photosynthesis and plant growth.

How can plants be infected by fungal pathogens?

Fungal pathogens can enter plants and grow through their tissues.

What is one example of a fungal plant disease?

Rose black spot.

What are the symptoms of rose black spot?

Purple or black spots develop on leaves, which can turn yellow and fall off.

How does rose black spot affect plants?

Loss of leaves reduces photosynthesis and therefore reduces plant growth.

How can the spread of rose black spot be reduced?

By removing and destroying infected leaves and using fungicides.

How can plants defend themselves against pathogens?

They have physical and chemical barriers.

What is one physical defence in plants?

Cellulose cell walls form a barrier against pathogens.

How do waxy cuticles help defend plants?

They form a waterproof barrier that helps prevent pathogens entering.

How do stomata help protect plants?

They can close to reduce the entry of pathogens.

What are antimicrobial chemicals?

Chemicals produced by plants that can kill or inhibit microorganisms.

What are chemicals in plants that deter herbivores?

Some plants produce chemicals that are toxic or unpleasant to herbivores, helping protect the plant.

What are physical barriers in humans?

The skin, hairs and mucus.

How does the skin defend against pathogens?

It forms a physical barrier that prevents pathogens entering the body.

How do hairs and mucus help defend the body?

Hairs trap pathogens and mucus traps them so they can be removed.

How do ciliated cells help defend the airways?

Cilia move mucus containing trapped pathogens towards the throat, where it can be swallowed.

What is the role of the stomach acid in defence?

Hydrochloric acid creates a low pH that can kill pathogens swallowed with food.

What is the immune system?

The body's defence system against pathogens.

What are white blood cells?

Cells that defend the body against pathogens.

How do white blood cells engulf pathogens?

They surround and take in pathogens, then digest them. This is called phagocytosis.

What is phagocytosis?

The process in which a white blood cell engulfs and digests a pathogen.

What are antibodies?

Proteins produced by white blood cells that bind to specific antigens on pathogens.

Why are antibodies specific?

Each antibody has a shape complementary to a particular antigen.

What happens when antibodies bind to pathogens?

They can help destroy the pathogen or mark it for destruction by other immune cells.

What are antitoxins?

Substances produced by white blood cells that neutralise toxins released by pathogens.

What is a vaccine?

A preparation containing a harmless form of a pathogen or its antigens that stimulates an immune response.

How does vaccination protect against disease?

It causes the immune system to produce antibodies and memory cells, allowing a faster response if the pathogen is encountered again.

What are memory cells?

Cells that remain in the body after an infection or vaccination and allow a faster antibody response if the same pathogen enters again.

Why can vaccination reduce the spread of communicable diseases?

A high proportion of vaccinated people are less likely to become infected and transmit the pathogen.

What is herd immunity?

Protection of a population that occurs when enough people are immune that the pathogen has difficulty spreading.

Why are some people unable to be vaccinated?

Some people may have medical reasons that prevent them from receiving certain vaccines.

What are antibiotics?

Medicines that kill bacteria or stop them reproducing.

Do antibiotics kill viruses?

No. Antibiotics do not work against viruses.

Why don't antibiotics work against viruses?

Viruses reproduce inside cells and do not have the structures targeted by antibiotics.

Why is it important to complete a course of antibiotics?

To help ensure the infection is treated effectively and reduce the chance of resistant bacteria surviving.

What is antibiotic resistance?

The ability of bacteria to survive an antibiotic that would normally kill them.

How does antibiotic resistance develop?

Random mutations can make some bacteria resistant. Antibiotics kill susceptible bacteria, leaving resistant bacteria to survive and reproduce.

Why is antibiotic resistance a problem?

It can make bacterial infections harder to treat.

How can the development of antibiotic resistance be slowed?

By using antibiotics only when necessary and not using them to treat viral infections.

Why are new antibiotics needed?

Some bacteria have become resistant to existing antibiotics.

What is a painkiller?

A medicine that reduces pain but does not kill pathogens.

What is a drug?

A substance that changes the way the body works.

What is a placebo?

A treatment that does not contain the active drug being tested.

What is a double-blind trial?

A trial in which neither the participants nor the researchers directly assessing the results know who receives the treatment and who receives the control.

Why are double-blind trials useful?

They reduce bias when assessing the effects of a treatment.

What is a clinical trial?

A test of a medical treatment involving human participants.

What happens before a drug is tested on humans?

It is tested in laboratories and may be tested on cells, tissues and animals to assess safety and effectiveness.

What is the placebo effect?

A person may experience an improvement because they believe they are receiving an effective treatment, even if they receive a placebo.

Why are clinical trials controlled?

To allow the effects of the new treatment to be compared with a control or existing treatment.

What is the role of peer review in scientific research?

Other scientists assess research before it is published to help identify errors and assess its quality.

What is a non-communicable disease?

A disease that cannot be directly passed from one person to another.

What is a risk factor?

A factor that increases the likelihood of developing a disease.

What is a correlation?

An association between two variables where a change in one is linked with a change in the other.

Does correlation always mean one factor causes the other?

No. Correlation does not necessarily mean causation.

What are examples of risk factors for non-communicable diseases?

Smoking, poor diet, lack of exercise, alcohol consumption and exposure to some substances or conditions.

What is a disease risk factor that can be linked to both genetics and lifestyle?

Obesity can be influenced by genetic factors and by diet and physical activity.

How can smoking increase the risk of disease?

It can increase the risk of cardiovascular disease and lung disease and contains chemicals that can damage the body.

How can obesity increase the risk of disease?

It is associated with an increased risk of conditions such as type 2 diabetes and cardiovascular disease.

What is cardiovascular disease?

A disease affecting the heart or blood vessels.

How can coronary heart disease be linked to lifestyle?

Risk factors include smoking, an unhealthy diet, lack of exercise and obesity.

Why can data about disease risk factors be difficult to interpret?

There may be other variables affecting the results, and correlation does not necessarily prove that one factor causes another.

How can scientists investigate whether a factor is linked to disease?

They can collect data from large groups of people and compare disease rates between groups with different levels of exposure to the factor.