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 15 of 18 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 15 of 18
Practice
19 questions
Recall
22 flashcards
Memory Aids
SMA — Three categories of non-specific defence:
- S — Skin (physical barrier; sebum creates acidic pH)
- M — Mucus and cilia (trap and sweep pathogens out of airways)
- A — Acid (stomach acid kills ingested pathogens)
Phagocytosis steps — RAEFD:
- R — Recognise the pathogen as foreign
- A — Attach to the pathogen surface
- E — Engulf it (cell membrane folds around it)
- F — Fuse with lysosome
- D — Digest with enzymes
Signs of inflammation — RSHP: Redness, Swelling, Heat, Pain. All four have a biological reason: redness and heat = vasodilation (more blood flow); swelling = fluid leaving capillaries; pain = inflammatory chemicals stimulating nerve endings.
Neutrophils vs Macrophages: Neutrophils are "first responders" (arrive fast, die fast, many of them). Macrophages are "generals" (arrive later, live longer, present antigens to trigger the adaptive immune system). Think of neutrophils as the emergency services and macrophages as the investigators who then call in specialist forces.
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 epithelium for much longer. This gives bacteria like Pseudomonas aeruginosa time to multiply, invade tissue, 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: A student cuts their finger and notices that over the next few hours the area becomes red, warm, swollen, and painful. Explain the biological cause of each of these four signs of inflammation.
When tissue is damaged, mast cells and damaged cells release histamine and other chemical mediators. This triggers the inflammatory response: (1) Redness: blood vessels in the area dilate (vasodilation), increasing blood flow to the site, causing the red colour. (2) Warmth: the increased blood flow brings warm blood to the surface area. (3) Swelling: histamine increases capillary permeability, allowing fluid (plasma) and white blood cells to leak out of blood vessels into the surrounding tissue. Fluid accumulation causes swelling (oedema). (4) Pain: inflammatory chemicals such as prostaglandins directly stimulate nearby pain receptors (nociceptors), causing the sensation of pain. These responses together increase delivery of white blood cells (especially neutrophils) to fight any pathogens that entered through the wound.
Quick Check: Compare and contrast the roles of neutrophils and macrophages in the non-specific immune response. Include at least three differences.
Both neutrophils and macrophages are phagocytes that engulf and destroy pathogens by phagocytosis. However, they differ in several key ways: (1) Speed of response: neutrophils arrive at infection sites within 30 minutes; macrophages arrive later. (2) Lifespan: neutrophils live only 6-7 hours and die after engulfing pathogens (their dead bodies form pus); macrophages can live for months. (3) Size: macrophages are much larger and can engulf bigger pathogens and debris. (4) Additional function: macrophages act as antigen-presenting cells — after digesting pathogens, they display fragments (antigens) on their surface to activate T lymphocytes, linking non-specific and specific immunity. Neutrophils do not have this antigen-presenting role. (5) Abundance: neutrophils make up 50-70% of all white blood cells; macrophages are tissue-resident and less numerous.