Memory Aids
Part of Human Defense Systems - Non-specific — GCSE Biology
This memory aid covers Memory Aids within Human Defense Systems - Non-specific for GCSE Biology. Physical and chemical barriers, white blood cell responses, inflammatory response It is section 12 of 16 in this topic. Use it for quick recall, then test yourself straight afterwards so the memory aid becomes usable in an answer.
Topic position
Section 12 of 16
Practice
19 questions
Recall
22 flashcards
Memory Aids
SMA — Three categories of non-specific defence:
- S — Skin (physical barrier; skin oils help maintain the barrier)
- M — Mucus and cilia (trap and sweep pathogens out of airways)
- A — Acid (stomach acid kills ingested pathogens)
Phagocytosis steps — DED:
- D — Detect chemicals from the pathogen
- E — Engulf it (cell membrane surrounds and takes it in)
- D — Digest with enzymes inside the cell
Mucus and cilia work as a pair: Mucus traps the pathogens; cilia move the mucus. Never describe one without the other. If cilia are damaged (e.g., by smoking), mucus cannot be swept away — pathogens stay in the airways and infection is more likely. This is a favourite exam application.
Quick Check: A person with cystic fibrosis has thick, sticky mucus that their cilia cannot sweep effectively. Explain why these patients are significantly more susceptible to respiratory infections than healthy individuals.
In healthy airways, mucus traps pathogens (bacteria, viruses, particles) and cilia beat rhythmically to sweep this mucus upward towards the throat, removing trapped pathogens before they can cause infection. In cystic fibrosis, the mucus is abnormally thick and viscous, so cilia cannot move it effectively. Pathogens become trapped in the airways and remain in contact with the respiratory surface for much longer. This gives bacteria time to multiply and establish infection. The first line of non-specific defence (the ciliary escalator) is therefore impaired, making respiratory infections far more likely and harder to clear.
Quick Check: State three ways in which the body prevents pathogens from entering internal tissues.
Any three from: (1) Skin acts as a physical barrier, preventing pathogens from penetrating into underlying tissues. (2) Mucus in the nose and airways traps pathogens before they can reach the lungs. (3) Cilia sweep mucus (with trapped pathogens) upward to the throat where they are swallowed. (4) Stomach acid (pH ~2) kills most pathogens that are swallowed. (5) Lysozyme in tears and saliva destroys the cell walls of bacteria. (6) Blood clots seal wounds to stop pathogens entering through damaged skin.