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KS3 Science · Year 8Chapter 4 · Health, disease and the immune system
Year 8 · Chapter 4

Health, disease and the immune system

By the end of this chapter you will be able to

  • Distinguish communicable from non-communicable diseases, and name the four types of pathogen
  • Describe the body’s first and second lines of defence
  • Explain how vaccination protects a person and a community
  • Describe lifestyle factors that raise the risk of some diseases, and say why a link is not always a cause
  • Explain what antibiotics and painkillers do, and why resistance matters

You should already know

  • Cells and microorganisms (Year 7 Chapter 2)
  • Respiration and energy (Year 8 Chapter 3)

Where this leads

  • Nervous system and reflexes (Year 8 Chapter 6)

National Curriculum for England, Key Stage 3 science, Year 8. Content: 8B6 communicable (pathogen) and non-communicable diseases; viruses, bacteria, fungi and protists; the body’s defences (skin, mucus, white blood cells, antibodies); vaccination; lifestyle factors and the risk of disease; antibiotics and painkillers (basic).

Exercise P  Do you remember?

1
FWhat is the name for a microorganism or other agent that causes disease? Write the word.
2
FWhat is half of 90? Write the number.
3
FWhat is the name of the organ that pumps blood around the body? Write the word.
4
FWhat is 250 divided by 5? Write the number.
5
FWhat is the name of the layer that covers and protects the outside of the body? Write the word.
4.1

Pathogens and disease

Year 8
8B6: communicable (pathogen) and non-communicable diseases; viruses, bacteria, fungi and protists
Video lesson: Pathogens and diseaseComing soon
Story. Ruby has a cold and stays home for three days. “Did I catch it from someone?” she asks. Her teacher explains that some diseases are caused by pathogens that can pass from person to person, and some are not caused by pathogens at all.

A communicable disease is caused by a pathogen and can pass from one person to another. A non-communicable disease is not caused by a pathogen and cannot be passed on by infection, for example heart disease.

The four main types of pathogen are viruses, bacteria, fungi and protists. A virus is not a cell and must enter a host cell to reproduce. A bacterium is a single cell that can reproduce on its own. A fungus grows as thread-like hyphae. A protist is a single-celled organism, and some protists are parasites.

virusbacteriumfungusprotistDrawings show shape and size only; they are not to scale.
Simple drawings of the four types of pathogen: a virus, a bacterium, a fungus and a protist.

The table compares the four types.

PathogenExampleHow it spreadsKey feature
virusinfluenza (flu)droplets from coughs and sneezescannot reproduce without a host cell
bacteriumsalmonellacontaminated fooda single cell that can reproduce on its own
fungusathlete’s footdirect contact with an infected person or surfacegrows as thread-like hyphae
protistmalariabites from an infected mosquitoa single-celled organism that can be a parasite

Key ideas

  • A communicable disease is caused by a pathogen and can be passed on.
  • A non-communicable disease is not caused by a pathogen.
  • Viruses are not cells and must enter a host cell to reproduce.
  • Bacteria, fungi and protists are living organisms; viruses are not.
Worked example 4.1.1
Which type of pathogen is not a cell and must enter a host cell to reproduce? Write the word.

Method. Recall the type of pathogen.

  1. Recall. A virus is not a cell and needs a host cell to reproduce.
    host cell
  2. Name it. So the pathogen is a virus.
    virus
  3. Write the answer.
    virus

Check. Influenza is caused by a virus. ✓

Worked example 4.1.2
Is heart disease communicable or non-communicable? Write the word.

Method. Check whether a pathogen causes it.

  1. Check. Heart disease is not caused by a pathogen and is not passed on by infection.
    not passed on
  2. Decide. So it is non-communicable.
    non-communicable
  3. Write the answer.
    non-communicable

Check. Lifestyle can raise the risk of heart disease. ✓

Worked example 4.1.3
Name the pathogen type that causes malaria. Write the word.

Method. Recall the example.

  1. Recall. Malaria is caused by a protist, a single-celled parasite.
    protist
  2. Name it. So the type is a protist.
    protist
  3. Write the answer.
    protist

Check. Mosquitoes spread the protist. ✓

Watch out

Watch out: antibiotics do not kill viruses. A cold or flu is caused by a virus, so antibiotics do not work on it.

Exam tip

Exam tip. Name the pathogen, then give one key feature: a virus is not a cell; a bacterium is one cell; a fungus has hyphae; a protist is single-celled.

Try it (with your teacher, or a grown-up at home). Look at the pathogen drawings and the table. Say which pathogen could be spread by a cough and which by a mosquito. Do not handle any real sample.

Exercise 4A  Pathogens and disease

1
FWhat is the name for a disease that can pass from one person to another? Write the word.
2
FIs a non-communicable disease caused by a pathogen? Write yes or no.
3
FWhich type of pathogen is a single-celled organism that can reproduce on its own? Write the word.
4
FWhich type of pathogen grows as thread-like hyphae? Write the word.
5
FWhich type of pathogen causes influenza (flu)? Write the word.
6
FWhich type of pathogen causes malaria? Write the word.
7
FIs a virus a living cell? Write yes or no.
8
FName the disease that is non-communicable and linked to smoking. Write the words.
9
PSWhich pathogen is spread by contaminated food: salmonella or influenza? Write the word.
10
PSAli says a cold is caused by a bacterium, so antibiotics will cure it. Is Ali right? Write yes or no.
11
PSWorking scientifically: a pupil lists three diseases and sorts them into communicable and non-communicable. Which of these is communicable: measles, or heart disease? Write the word.
12
RExplain why a virus cannot be killed by a medicine that only kills bacteria. Write one sentence.
13
RChallenge: explain why a disease can be communicable but not caused by a bacterium. Write one sentence.
4.2

The body’s defences

Year 8
8B6: the body’s defences: skin, mucus, stomach acid, white blood cells that engulf pathogens, and antibodies
Video lesson: The body’s defencesComing soon
Story. Omar cuts his finger on a tin. Within a few hours the cut has closed and is starting to heal. “What stopped the germs getting in?” he asks. His teacher says, “The skin is the first line of defence. If a germ does get in, white blood cells and antibodies are the second line.”

The body has several defences against pathogens:

An antigen is a molecule on a pathogen that the immune system recognises. An antibody fits its antigen, like a key in a lock, and helps to destroy the pathogen.

phagocyte engulfs a pathogenantibody binds an antigenantibodyantigen
A white blood cell engulfing a pathogen, and an antibody binding to an antigen.

Key ideas

  • The skin and mucus are the first line of defence.
  • Stomach acid kills many swallowed pathogens.
  • White blood cells engulf pathogens or make antibodies.
  • An antibody binds to a specific antigen.
Worked example 4.2.1
What is the first line of defence that acts as a barrier to pathogens? Write the word.

Method. Recall the barrier.

  1. Recall. The skin covers the body and is a physical barrier.
    physical barrier
  2. Name it. So the first line is the skin.
    skin
  3. Write the answer.
    skin

Check. Mucus is also a first line defence. ✓

Worked example 4.2.2
What is the name of the white blood cell that engulfs pathogens? Write the word.

Method. Recall the cell.

  1. Recall. A white blood cell that engulfs pathogens is a phagocyte.
    phagocyte
  2. Name it. So the answer is phagocyte.
    phagocyte
  3. Write the answer.
    phagocyte

Check. Phagocytes are a type of white blood cell. ✓

Worked example 4.2.3
What do antibodies bind to on a pathogen? Write the word.

Method. Recall the target.

  1. Recall. An antibody fits a specific molecule on the pathogen, called an antigen.
    antigen
  2. Name it. So antibodies bind to antigens.
    antigen
  3. Write the answer.
    antigen

Check. Each antibody fits one antigen. ✓

Watch out

Watch out: an antibody is not a pathogen. It is a protein made by white blood cells that binds to a specific antigen.

Exam tip

Exam tip. Name the defence and say what it does: “mucus traps pathogens”, “phagocytes engulf pathogens”.

Try it (with your teacher, or a grown-up at home). Look at the picture of the phagocyte and the antibody. Describe, in your own words, how each one stops a pathogen. Do not touch any cut or wound on yourself or others.

Exercise 4B  The body’s defences

1
FWhich organ is the body’s largest physical barrier against pathogens? Write the word.
2
FWhat substance traps pathogens in the airways and gut? Write the word.
3
FWhat are the small hairs in the airways called? Write the word.
4
FWhich part of the digestive system kills many swallowed pathogens? Write the words.
5
FWhich white blood cells engulf pathogens? Write the word.
6
FWhat do white blood cells make to fit an antigen? Write the word.
7
FWhat is the name of the molecule on a pathogen that the immune system recognises? Write the word.
8
FIs the skin a first line of defence? Write yes or no.
9
FDoes an antibody itself destroy every pathogen on its own? Write yes or no.
10
PSRuby says that stomach acid is a first line defence. Is Ruby right? Write yes or no.
11
PSWorking scientifically: a pupil wants to show the effect of a barrier. Name one barrier a pupil could use to test a model of the skin. Accept any sensible barrier: cling film, or a sheet of paper.
12
RExplain why the body needs both physical and chemical defences. Write one sentence.
4.3

Vaccination and immunity

Year 8
8B6: vaccination, and how the immune system remembers a pathogen after an infection or a vaccine
Video lesson: Vaccination and immunityComing soon
Story. Sam’s grandmother had a disease when she was a child, and she never caught it again. “Why not?” he asks. His teacher says, “Her immune system made memory cells. When the same pathogen came back, it made antibodies much faster.”

When a pathogen first enters the body, the white blood cells take time to make the right antibodies. Some white blood cells become memory cells. If the same pathogen returns, the memory cells respond quickly, so the person is usually protected.

A vaccine contains a harmless form of a pathogen, or its antigen. It makes the body produce antibodies and memory cells without the person becoming seriously ill. This is called immunity.

When most people in a community are vaccinated, a disease spreads less easily, which protects those who cannot be vaccinated. This is called herd immunity.

The table gives example data for cases of one communicable disease in a town. A vaccination programme started in 2018.

YearCases
2016240
2017210
2018120
201960
202030
Cases of the disease per year (example data)240201621020171202018602019302020Blue: before vaccination. Green: after vaccination began in 2018.
Bar chart of cases per year, falling after vaccination began in 2018.

Key ideas

  • A vaccine trains the immune system without causing serious illness.
  • Memory cells respond quickly when the same pathogen returns.
  • Herd immunity protects those who cannot be vaccinated.
  • Vaccination has reduced many communicable diseases.
Worked example 4.3.1
Using the example data, how many fewer cases were there in 2020 than in 2016? Write the number.

Method. Subtract the later value from the earlier.

  1. Read. There were 240 cases in 2016 and 30 cases in 2020.
    240 and 30
  2. Calculate. The difference is 240 minus 30.
    240 - 30 = 210
  3. Write the answer.
    210

Check. 30 + 210 = 240. ✓

Worked example 4.3.2
What do vaccines contain that makes the immune system respond? Write the word.

Method. Recall the content of a vaccine.

  1. Recall. A vaccine contains a harmless form of a pathogen, or its antigen.
    antigen
  2. Name it. The part that makes the immune system respond is the antigen.
    antigen
  3. Write the answer.
    antigen

Check. The vaccine is not a full infection. ✓

Worked example 4.3.3
What are the cells called that remain after an infection and respond quickly to the same pathogen again? Write the words.

Method. Recall the cells.

  1. Recall. Some white blood cells become memory cells.
    memory cells
  2. Name them. The cells that remain are called memory cells.
    memory cells
  3. Write the answer.
    memory cells

Check. Memory cells give a faster response. ✓

Watch out

Watch out: vaccination does not give immunity by stopping the pathogen. It trains the immune system so that it can respond quickly.

Exam tip

Exam tip. Explain herd immunity in one sentence: most people vaccinated means the pathogen spreads less, protecting the few who cannot be vaccinated.

Try it (with your teacher, or a grown-up at home). Look at the bar chart. Say when the cases began to fall, and what happened to the number of cases between 2019 and 2020. Discuss with your class why the data is example data, not evidence for any one town.

Exercise 4C  Vaccination and immunity

1
FWhat is a vaccine? Write the word: a medicine, a pathogen, or a cell.
2
FWhat do white blood cells remember after an infection? Write the words.
3
FWhat is the name of the protection that a community gets when many people are vaccinated? Write the words.
4
FUsing the example data, how many cases were there in 2019? Write the number.
5
FUsing the example data, what is the fall in cases from 2018 to 2019? Write the number.
6
FIn which year did the cases first fall to below 100? Write the year.
7
FIs a vaccine made from a live, fully infectious pathogen? Write yes or no.
8
FWhat is the name of the molecule in a vaccine that makes the immune system respond? Write the word.
9
PSAli says that once you have had a disease you can never catch it again, because of memory cells. Is Ali right? Write yes or no.
10
PSWorking scientifically: the table shows the cases in 2016 and 2020. Which year had more cases? Write the year.
11
RExplain why vaccination protects people who cannot be vaccinated. Write one sentence.
4.4

Lifestyle and the risk of disease

Year 8
8B6: lifestyle factors (smoking, diet, physical activity, alcohol) and the risk of non-communicable disease
Video lesson: Lifestyle and the risk of diseaseComing soon
Story. Ali’s uncle has heart disease. “Could something he did have caused it?” Ali asks. His teacher says, “Lifestyle factors can raise the risk. But a factor that is linked to a disease is not always the cause, and each person is different.”

A risk factor is something that increases the chance of developing a disease. Many risk factors affect non-communicable diseases. Some of the main lifestyle risk factors are shown in the table.

Scientists use evidence from large groups of people to find links. A correlation between a factor and a disease shows that they occur together, but it does not prove that one causes the other.

FactorDiseases it raises the risk of
smokinglung cancer, heart disease, bronchitis
a diet high in salt, fat and sugarhigh blood pressure, heart disease, type 2 diabetes
too little physical activityobesity, heart disease, type 2 diabetes
drinking too much alcoholliver disease, some cancers

Key ideas

  • A risk factor increases the chance of developing a disease.
  • Smoking, diet, physical activity and alcohol are lifestyle risk factors.
  • A link between a factor and a disease does not always mean it is the cause.
  • Many people with a risk factor never develop the disease.
Worked example 4.4.1
Name one lifestyle factor linked to lung cancer and bronchitis. Write the word.

Method. Find the factor in the table.

  1. Look. Smoking is linked to lung cancer, heart disease and bronchitis.
    lung cancer
  2. Name it. So the factor is smoking.
    smoking
  3. Write the answer.
    smoking

Check. Smoking is a lifestyle risk factor. ✓

Worked example 4.4.2
Which disease is linked to too little physical activity? Write the words.

Method. Find the factor in the table.

  1. Look. Too little physical activity is linked to obesity, heart disease and type 2 diabetes.
    obesity
  2. Name one. Accept any one: obesity, heart disease, or type 2 diabetes.
    obesity
  3. Write the answer.
    Accept any one: obesity, heart disease, or type 2 diabetes.

Check. The table lists several linked diseases. ✓

Worked example 4.4.3
Is a link between a risk factor and a disease the same as proof that one causes the other? Write yes or no.

Method. Think about evidence.

  1. Think. A correlation shows two things occur together.
    occur together
  2. Decide. It does not prove the cause, so the answer is no.
    no
  3. Write the answer.
    no

Check. Evidence from many people is needed. ✓

Watch out

Watch out: a risk factor raises the chance; it does not mean a person will definitely get the disease, and not everyone with the disease had the factor.

Exam tip

Exam tip. Say “linked to” or “raises the risk of”, not “causes”, unless the evidence shows a cause.

Try it (with your teacher, or a grown-up at home). Make a list of the lifestyle risk factors in the table. For each one, write one sentence saying which disease it is linked to, using “raises the risk of”. Do not give medical advice to anyone; ask a grown-up or a doctor about health concerns.

Exercise 4D  Lifestyle and the risk of disease

1
FWhat is the word for something that increases the chance of developing a disease? Write the words.
2
FIs heart disease communicable or non-communicable? Write the word.
3
FWhich lifestyle factor is linked to bronchitis? Write the word.
4
FWhich lifestyle factor is linked to liver disease? Write the words.
5
FName one disease linked to a diet high in salt, fat and sugar. Accept any one: high blood pressure, heart disease, or type 2 diabetes.
6
FIs a link between a factor and a disease proof that the factor causes the disease? Write yes or no.
7
FDoes every person who smokes develop lung cancer? Write yes or no.
8
FIs physical activity a risk factor for heart disease in the table? Write yes or no.
9
PSWorking scientifically: a pupil finds that people who exercise more have fewer cases of heart disease. What kind of pattern is this? Write the word: correlation or cause.
10
PSAli says that because his uncle smokes, smoking caused his uncle’s heart disease. Is Ali right? Write yes or no.
11
RExplain why evidence from many people is used to link a lifestyle factor to a disease. Write one sentence.
12
RChallenge: explain why a link between a factor and a disease is not enough to say the factor is the cause. Write one sentence.
4.5

Antibiotics, painkillers and resistance

Year 8
8B6: antibiotics and painkillers (basic); antibiotic resistance
Video lesson: Antibiotics, painkillers and resistanceComing soon
Story. Ruby’s sister has a bacterial infection, and the doctor prescribes an antibiotic. Ruby has a headache from the same illness, and takes a painkiller. “They both help me feel better,” she says. Her teacher says, “They work in different ways, and only one kills the bacteria.”

An antibiotic kills bacteria, or stops them reproducing. It does not work on viruses. A painkiller relieves symptoms, such as pain or fever, but does not kill the pathogen.

Antibiotic resistance happens when a bacterium changes so that an antibiotic no longer kills it. Bacteria that survive by chance pass on their resistance, so over time more resistant bacteria are left. This is natural selection. Antibiotics should be used only when a doctor says they are needed.

The table compares the two kinds of medicine.

MedicineWhat it does
antibiotickills bacteria; does not work on viruses
painkillerrelieves symptoms, such as pain; does not kill the pathogen

Key ideas

  • Antibiotics kill bacteria and do not work on viruses.
  • Painkillers relieve symptoms but do not kill the pathogen.
  • Resistance develops by natural selection, when bacteria survive an antibiotic.
  • Use antibiotics only as a doctor advises.
Worked example 4.5.1
Do antibiotics work on viruses? Write yes or no.

Method. Recall what antibiotics target.

  1. Recall. Antibiotics target bacteria, not viruses.
    target bacteria
  2. Decide. So the answer is no.
    no
  3. Write the answer.
    no

Check. A cold is caused by a virus. ✓

Worked example 4.5.2
What does a painkiller do to the pathogen? Write the words.

Method. Recall what painkillers do.

  1. Recall. A painkiller relieves symptoms but does not kill the pathogen.
    does not kill
  2. Name it. It does not kill the pathogen.
    does not kill the pathogen
  3. Write the answer.
    does not kill the pathogen

Check. Painkillers treat the symptoms. ✓

Worked example 4.5.3
Write the word for a bacterium that can survive an antibiotic.

Method. Recall the process.

  1. Recall. Bacteria that survive an antibiotic pass on resistance by natural selection.
    natural selection
  2. Name it. The bacterium is a resistant bacterium.
    resistant
  3. Write the answer.
    resistant

Check. Resistance is inherited by the next generation. ✓

Watch out

Watch out: an antibiotic does not stop a virus. It is wrong to say that antibiotics cure colds or flu.

Exam tip

Exam tip. Say what the medicine does: an antibiotic kills bacteria; a painkiller relieves the symptoms.

Try it (with your teacher, or a grown-up at home). Look at the table and explain in one sentence why antibiotics are not used for a cold. Do not take any medicine, and ask a grown-up or a doctor about any medicine you are offered.

Exercise 4E  Antibiotics, painkillers and resistance

1
FWhat type of pathogen is killed by an antibiotic? Write the word.
2
FDo antibiotics work on viruses? Write yes or no.
3
FWhat does a painkiller do? Write the words.
4
FDoes a painkiller kill the pathogen? Write yes or no.
5
FWhat is the name for the process in which resistant bacteria survive and become more common? Write the words.
6
FIs antibiotic resistance caused by the antibiotic making bacteria change on purpose? Write yes or no.
7
FWhich type of medicine is used to relieve pain: antibiotic or painkiller? Write the word.
8
FWhich medicine is used to kill bacteria: antibiotic or painkiller? Write the word.
9
PSRuby says that a cold can be cured by an antibiotic, because colds are infections. Is Ruby right? Write yes or no.
10
PSWorking scientifically: a doctor says a cold does not need an antibiotic. Give one reason. Accept any reason: a cold is caused by a virus, and antibiotics only work on bacteria.
11
RExplain why using antibiotics when they are not needed can increase resistance. Write one sentence.
12
RChallenge: explain why a painkiller does not cure a bacterial infection, although it can make a person feel better. Write one sentence.

Chapter summary

SkillMethod
DiseasesCommunicable: caused by a pathogen and passed on. Non-communicable: not caused by a pathogen.
PathogensVirus (not a cell), bacterium, fungus (hyphae), protist (single-celled).
DefencesSkin and mucus first; stomach acid; phagocytes engulf; antibodies bind antigens.
VaccinationHarmless antigen trains the immune system; memory cells give quick protection; herd immunity.
LifestyleSmoking, diet, physical activity and alcohol are risk factors; a link is not proof of cause.
MedicinesAntibiotics kill bacteria only; painkillers relieve symptoms; resistance develops by natural selection.

Can you…?

  • I can distinguish communicable from non-communicable diseases and name the four types of pathogen
  • I can describe the body’s first and second lines of defence
  • I can explain how vaccination protects a person and a community
  • I can describe lifestyle risk factors and explain why a link is not always a cause
  • I can explain what antibiotics and painkillers do, and why resistance matters

Key terms

pathogen
a microorganism or other agent that causes disease
communicable disease
a disease caused by a pathogen that can pass from person to person
non-communicable disease
a disease that is not caused by a pathogen and is not passed on
phagocyte
a white blood cell that engulfs and destroys pathogens
antigen
a molecule on a pathogen that the immune system recognises
antibody
a protein made by white blood cells that binds to a specific antigen
vaccine
a medicine containing a harmless form of an antigen, to trigger immunity
herd immunity
protection of a community when most people are immune
antibiotic resistance
when bacteria survive an antibiotic and pass on the ability to survive

Exercise 4Z  Check-up

1
Which type of pathogen is not a cell and must enter a host cell to reproduce? Write the word.
2
Is heart disease a communicable disease? Write yes or no.
3
What is the name of the molecule on a pathogen that the immune system recognises? Write the word.
4
Which white blood cells engulf pathogens? Write the word.
5
What is the name of the substance that traps pathogens in the airways? Write the word.
6
Memory cells remember which kind of thing? Write the word: pathogen, or oxygen.
7
Using the example data, how many cases were there in 2018? Write the number.
8
Which medicine kills bacteria: antibiotic or painkiller? Write the word.
9
Name one lifestyle risk factor linked to type 2 diabetes. Accept any one: a diet high in salt, fat and sugar, or too little physical activity.
10
Explain why antibiotics do not work against a virus. Write one sentence.

Total 16 marks. Allow about 16 minutes.

Exercise 4X  Practice test questions

1
FName the four types of pathogen. Write the four words.[2 marks]
2
FName the first line of defence that covers the body. Write the word.[1 mark]
3
RDescribe the role of a phagocyte. Write one sentence.[2 marks]
4
FWhat is the name of the molecule that an antibody fits? Write the word.[1 mark]
5
RExplain how a vaccine protects a person without them becoming ill. Write one sentence.[2 marks]
6
PSUsing the example data, what was the fall in cases from 2016 to 2019? Write the number.[2 marks]
7
FName one lifestyle factor linked to heart disease. Accept any one: smoking, a diet high in salt, fat and sugar, too little physical activity.[1 mark]
8
RExplain why a correlation between a factor and a disease is not proof of a cause. Write one sentence.[2 marks]
9
FWhich medicine relieves the symptoms of a headache but does not kill the pathogen: an antibiotic or a painkiller? Write the word.[1 mark]
10
RExplain why bacteria may become resistant to an antibiotic. Write one sentence.[2 marks]
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