School › Immune system › Ages 15–16
Innate and adaptive immunity
Non-specific defences, phagocytosis, antigens and antibodies, B and T lymphocytes, primary and secondary responses and vaccination. With a quantitative handwashing investigation.
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Innate immunity is non-specific and present before any infection. It includes barriers (skin keratin, mucus, enzymes in tears and saliva, stomach acid), phagocytes, natural killer cells, inflammation and fever, which inhibits pathogen growth.[2]
Phagocytes such as neutrophils, macrophages and dendritic cells engulf pathogens; lysosomes digest them. Neutrophils make up about 50–60% of white blood cells. Dendritic cells then present antigens on their surface, triggering adaptive immunity.[3]
An antigen is a molecule that stimulates an immune response. B lymphocytes mature in the bone marrow and T lymphocytes in the thymus. A person has hundreds of millions of different B cells, each recognising a different antigen.[4][3][5]
Activated B cells become plasma cells that secrete antibodies: Y-shaped proteins of two heavy and two light chains whose variable regions bind one specific antigen. Helper T cells release cytokines; cytotoxic T cells destroy infected cells.[5][4]
The primary response takes days or even weeks. Memory cells make the secondary response faster, producing tens to hundreds of times more antibody.[5]
Vaccination exposes the body to non-infectious antigens from a known pathogen, giving a mild primary response and immune memory without the disease.[4]
Hand hygiene reduces transmission: scrubbing with soap for 20 seconds removes more germs than shorter washing, because lather forms micelles that trap and remove them. Water temperature makes no difference.[7][6]
Try it: Does scrubbing time matter?
You need
- Washable paint or hand cream mixed with fine biodegradable glitter
- Liquid soap, water and paper towels
- Stopwatch
- A transparent grid (1 cm squares) or a phone camera
- Results table
Safety
Use biodegradable glitter and washable paint or cream; check for skin allergies first. Keep hands away from eyes. Wipe up water to prevent slips. Results are for learning, not for judging anyone's hygiene.
What to do
- Agree a fixed amount of cream-and-glitter (for example one pea-sized blob) and rub it evenly over both hands.
- Count the glitter specks in three marked 1 cm squares on the back of one hand. Take the mean as the 'before' value.
- Wash with soap and water for a set time: 0 s (rinse only), 5 s, 10 s or 20 s of scrubbing. Each group tests one time; keep water flow and soap volume the same.
- Dry gently and count the specks in the same three squares again.
- Calculate the percentage removed = (before − after) ÷ before × 100. Pool class results, find the mean and range for each time, and plot % removed against scrub time.
What happens, and why?
Soap lather forms micelles that trap and lift particles, and longer scrubbing removes more, which is why 20 seconds is recommended. The glitter is only a model: real microbes are far smaller, but the trend matches what studies of handwashing show.[7]
Play: Innate or adaptive?
Sort each term: non-specific barrier, innate cell or response, or specific adaptive immunity?
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Quiz
Other ages: Ages 6–7 · Ages 10–11