Practise Human defence systems. 14 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
How your body stops pathogens getting in (the non-specific defences of the skin, nose, trachea and bronchi, and stomach) and how white blood cells destroy pathogens that do get in. A favourite for 'describe' and 'explain' questions, often in unfamiliar contexts such as smoking.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Name the body's non-specific defencesThe skin, the nose, the trachea and bronchi, and the stomach.
4
Describe how each defence stops pathogensSkin is a barrier; mucus traps pathogens; cilia move the mucus away; stomach acid kills pathogens.
4
Name three ways white blood cells defendPhagocytosis, producing antibodies and producing antitoxins.
5
Describe phagocytosisA white blood cell engulfs a pathogen and digests it.
6
Explain how antibodies and antitoxins workAntibodies bind to specific antigens on pathogens; antitoxins bind to the toxins made by bacteria and neutralise them.
7
Explain why antibodies are specificEach antibody fits only one antigen, so it binds to only one type of pathogen.
7
Explain effects of damage to a defenceE.g. smoke stops cilia beating, so mucus and pathogens build up in the airways and infections are more likely.
Notes
Non-specific defences: keeping pathogens out
Skin: a physical barrier that pathogens cannot get through while it is unbroken. It also produces antimicrobial secretions that kill pathogens. If the skin is cut, the blood clots and a scab seals the wound.
Nose: hairs and sticky mucus trap particles, which may contain pathogens, from the air you breathe in.
Trachea and bronchi: cells lining them make mucus, which traps pathogens. Other cells have cilia (tiny hairs) that beat to move the mucus up to the throat, where it is swallowed.
Stomach: produces hydrochloric acid, which kills pathogens in food, drink and swallowed mucus.
These defences are non-specific: they work against all pathogens.
The immune system: white blood cells
If a pathogen gets into the body, the immune system tries to destroy it. White blood cells do this in three ways.
Phagocytosis: white blood cells called phagocytes engulf (surround) pathogens and digest them.
Antibody production: white blood cells called lymphocytes make antibodies. Antibodies bind to antigens (molecules such as proteins) on the surface of a pathogen. This helps to destroy the pathogens, e.g. by sticking them together so phagocytes can engulf them.
Antibodies are specific: each one fits the antigen of only one type of pathogen, so a different antibody is needed for each pathogen.
Antitoxin production: white blood cells make antitoxins, which bind to the toxins made by bacteria and neutralise them.
Why you can still get ill
The first time a pathogen gets in, it takes time for white blood cells to make the right antibodies.
Meanwhile the pathogen reproduces, so you may feel ill before it is destroyed.
Cheatsheet
Skin: physical barrier + antimicrobial secretions; scabs seal cuts
Nose: hairs and mucus trap particles
Trachea and bronchi: mucus traps pathogens; cilia move the mucus to the throat
Stomach: hydrochloric acid kills pathogens
White blood cells: phagocytosis, antibodies, antitoxins
Phagocytosis = engulfing and digesting a pathogen
Antigen = molecule (e.g. a protein) on the surface of a pathogen
Antibody: binds to a specific antigen on a pathogen
Antitoxin: neutralises a toxin made by bacteria
How to answer each type of question
Describe how a part of the body stops pathogens
2 marks4
Name what does the job (mucus, cilia, acid, skin).
Say what it does to the pathogens (traps, moves away, kills, keeps out).
Example. Describe how the trachea and bronchi protect the body against pathogens.
Show the model answer
Mucus traps pathogens (1). Cilia beat to move the mucus up to the throat, where it is swallowed (1).
Describe how white blood cells defend the body
3 marks5
Give three separate ways: phagocytosis, antibodies, antitoxins.
Add what each one does, not just its name.
Example. Describe three ways that white blood cells help to defend the body against pathogens.
Show the model answer
They engulf and digest pathogens (phagocytosis) (1). They produce antibodies, which bind to antigens on the pathogens (1). They produce antitoxins, which neutralise the toxins made by bacteria (1).
Explain the effect of damage to a defence
3 marks7
Work out which defence is affected and what it normally does.
Say what happens when it stops working.
Finish with the result: pathogens are more likely to infect the body.
Example. Chemicals in cigarette smoke stop cilia from beating. Explain why smokers are more likely to get chest infections.
Show the model answer
The cilia cannot move the mucus, with its trapped pathogens, up and out of the airways (1). So mucus and pathogens build up in the trachea, bronchi and lungs (1). So the pathogens are more likely to infect the cells of the airways and lungs (1).
Explain why antibodies are specific
2 marks7
Say that each antibody binds only to one antigen.
Say that different pathogens have different antigens.
Example. A child recovers from chickenpox, which is caused by a virus. Explain why the antibodies the child made against chickenpox do not protect the child against measles.
Show the model answer
Antibodies are specific: each antibody binds only to one antigen (1). The measles virus has different antigens from the chickenpox virus, so the chickenpox antibodies cannot bind to it (1).
Shortcuts and memory tricks
From outside in: skin, nose, trachea and bronchi, stomach = barrier, trap, sweep, acid.
Three jobs of white blood cells: eat them (phagocytosis), tag them (antibodies), neutralise their poisons (antitoxins).
Antibody vs antitoxin: an antibody targets the pathogen itself; an antitoxin targets the toxin.
Lock and key: an antibody fits one antigen, like a key fits one lock.
Where marks are lost
Mixing up antigen, antibody and antibiotic. Antigen = on the pathogen; antibody = made by white blood cells; antibiotic = a medicine that kills bacteria.
Saying white blood cells 'eat' pathogens without saying that they engulf and digest them.
Saying antibodies neutralise toxins. Antitoxins do that; antibodies bind to antigens on pathogens.
Saying stomach acid digests pathogens. It kills them.
Exam technique
Use the key words: barrier, mucus, cilia, hydrochloric acid, engulf, digest, antibodies, antigens, antitoxins.
For 'describe three ways white blood cells defend', give three different ways, each with what it does.
In unfamiliar contexts, work out which defence is affected and follow the consequences one step at a time.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Give two ways the skin helps to defend the body against pathogens.
It is a barrier; it produces antimicrobial secretions.
Some bacteria produce toxins. Name the substance produced by white blood cells that counteracts toxins.
Antitoxins
Pathogens can enter the body through the nose and mouth. Name the acid produced in the stomach.
Hydrochloric acid
The body has physical, chemical and cellular defences against pathogens. Name the acid produced in the stomach that kills pathogens.
Hydrochloric acid
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
The human body has several ways of stopping pathogens from entering it.
(a) Which part of the body produces an acid that kills pathogens? Tick (✓) one box.[1]
Nose
Skin
Stomach
Trachea
(b) Give two ways the skin helps to defend the body against pathogens.[2]
(c) The nose contains hairs and mucus. How do these help to defend the body?[1]
(d) Name the type of blood cell that helps to destroy pathogens that get into the body.[1]
Show the answer and mark scheme
(a)Answer: Stomach
(b)Answer: It is a barrier; it produces antimicrobial secretions.
it is a barrier (to pathogens)
it produces antimicrobial secretions (that kill pathogens)
scabs form over cuts to seal them
(c)
they trap particles that may contain pathogens
(d)Answer: White blood cells
white blood cell
Question 2Medium7 marks
The trachea and bronchi are lined with cells that help to stop pathogens reaching the lungs.
(a) Describe how the cells lining the trachea and bronchi stop pathogens reaching the lungs.[3]
(b) Chemicals in tobacco smoke stop cilia moving. Explain why smokers are more likely than non-smokers to get chest infections.[2]
(c) Explain how the stomach helps to defend the body against pathogens.[2]
Show the answer and mark scheme
(a)
(some cells) produce mucus
mucus traps pathogens / particles
cilia move / waft the mucus up to the throat, where it is swallowed
(b)
mucus (and trapped pathogens) is not moved out of the airways / builds up
(so) pathogens reach the lungs / stay in the airways and cause infection
(c)
the stomach produces (hydrochloric) acid
(the acid) kills pathogens (in food / drink / swallowed mucus)
Question 3Hard9 marks
Cystic fibrosis is an inherited disorder. People with cystic fibrosis produce very thick, sticky mucus in their airways. Cilia cannot move this mucus easily.
(a) Explain why people with cystic fibrosis get more lung infections than other people.[3]
(b) A physiotherapist claps on the chest and back of a person with cystic fibrosis to loosen the mucus, which the person then coughs up. Explain how this reduces the chance of infection.[2]
(c) In a study, 40 people with cystic fibrosis had a mean of 5.5 chest infections per year before they started daily physiotherapy and a mean of 3.3 chest infections per year afterwards. Calculate the percentage decrease in the mean number of chest infections.[2]
(d) Some people with cystic fibrosis take antibiotics every day, even when they do not have an infection. Suggest one advantage and one disadvantage of this.[2]
Show the answer and mark scheme
(a)
the mucus traps pathogens
the mucus is not moved out of the airways (by the cilia) / stays in the lungs
(so) pathogens stay in the lungs and reproduce / cause infection
warm, moist mucus is a good place for bacteria to grow
(b)
it removes mucus containing trapped pathogens from the lungs
(so) fewer pathogens remain to reproduce / cause infection
(c)Answer: 40%
(5.5 − 3.3) ÷ 5.5 × 100
40 (%)
(d)
advantage: kills bacteria before they can cause an infection
disadvantage: bacteria may become resistant to the antibiotic / the antibiotic may not work when it is needed / side effects