Explain mucus stomach acid and white-cell defence
Connect trapping, chemical conditions and cell responses with distinct functions.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Recall skin and nose hairs and blood-cell functions.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which property makes mucus useful for trapping?
What you will learn
- Trapping and acid act differently
- White cells respond after entry
Trapping and acid act differently
Mucus is a sticky secretion that traps particles and pathogens in passages such as the breathing system. Trapping holds material rather than automatically destroying every agent. Movement and clearance of trapped material help reduce its access to deeper surfaces; detailed ciliated-cell teaching belongs to the gas-exchange sequence.
Stomach acid creates acidic conditions that kill many swallowed pathogens. It is not an antibody and does not guarantee destruction of every pathogen, since some can survive or avoid this defence. Name the stomach as the relevant location and distinguish acid action from digestion by enzymes.
White cells respond after entry
White blood cells add internal defence. Phagocytes engulf pathogens and break them down inside the cell; relevant lymphocytes produce antibodies. This links the barrier sequence to the earlier blood lesson without assuming all white cells have identical functions or that every lymphocyte secretes antibodies.
When asked for body defences, include the required set: skin, hairs in the nose, mucus, stomach acid and white blood cells. Do not replace one with an unrelated structure. An answer should describe how each reduces entry or deals with a pathogen, keeping physical, chemical and cell actions separate.
Sources for this lesson
Pause and explain
Which pairing is correct?
Worked example
Which defence traps particles and which exposes swallowed pathogens to acidic conditions?
Show the worked solution
- Mucus is sticky.
- Stomach acid changes chemical conditions.
Answer Mucus traps particles; stomach acid kills many swallowed pathogens through acidic conditions.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain one defence role each for mucus, stomach acid and white blood cells.
Give me a hint
Use three distinct mechanisms.
Compare my reasoning
- Mucus traps particles; acid creates conditions that kill many swallowed pathogens.
- White cells use phagocytosis or antibody production.
Mucus traps; stomach acid kills many swallowed pathogens; white cells engulf pathogens or produce antibodies.
Look for these in your work
- Cover all three
- Keep mechanisms distinct
List all five body defences required here.
Give me a hint
Include the two physical defences from the previous lesson.
Compare my reasoning
- Recall skin and nose hairs.
- Add mucus, stomach acid and white blood cells.
Skin, hairs in the nose, mucus, stomach acid and white blood cells.
Look for these in your work
- Include all five
- Do not substitute symptoms
A pathogen survives stomach acid. Does this prove acid never provides defence?
Give me a hint
A general protection need not be universal.
Compare my reasoning
- Acid kills many pathogens.
- Survival by one type is compatible with that limited claim.
No; survival of one pathogen does not disprove stomach acid’s defence against many swallowed pathogens.
Look for these in your work
- Avoid an absolute claim
- State the biological limit
Common mistakes
- Equating mucus with antibodies.
- Claiming every white cell performs every defence function.
What can you explain now?
Which pairing is correct?
Compare with the explanation
Phagocytes engulf; relevant lymphocytes produce antibodies
The cell roles differ.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Describe all five defences in a sentence each, keeping the actions distinct.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.