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Bacteria get into a cut. How does your body find them and fight back?
Immune Response lab · Last updated: 16 October 2026
Bacteria get into a cut. What happens next? In this 3D lab, you follow the body's alarm signals and watch white blood cells hunt down and destroy invaders. It explains why cuts go red and swollen, why we sometimes run a fever and how vaccines help the body prepare in advance.
What you'll discover
- Damaged cells release chemical alarm signals that draw white blood cells to the wound.
- Some white blood cells swallow bacteria whole and digest them, while others make antibodies.
- The immune system remembers germs it has met, so a second attack is beaten off faster.
The science in plain words
Your skin is the first barrier against germs. When it is cut, bacteria can slip into the tissue underneath. Damaged cells and the immune cells already there release chemical signals that raise the alarm. Nearby blood vessels widen and become leaky, bringing extra blood and fluid. This is inflammation, and it is why a cut turns red, warm, swollen and sore.
White blood cells squeeze out of the tiny blood vessels and follow the chemical trail towards the highest concentration of signals, rather like following a smell to its source. Cells called phagocytes reach the bacteria, wrap around them and swallow them, then break them down inside. Pus is mainly dead white blood cells, bacteria and debris left from this battle.
If the infection is not cleared quickly, a slower and more targeted defence joins in. Lymphocytes recognise the particular germ; some make antibodies, proteins that stick to the invader and mark it for destruction. Afterwards, memory cells remain in the body. If the same germ returns, they respond much faster, often before you feel ill. Vaccines use this memory by showing the immune system a harmless version or part of a germ, so it is ready for the real thing.
Where it fits
- India, NCERT: Class 8 science, Chapter 3: Health: The Ultimate Treasure
- India, NCERT: How white blood cells work goes beyond the NCERT syllabus for classes 6 to 10; the lab builds on Class 8 health, disease and immunity.
- United States: Grades 6 to 12
- Next Generation Science Standards: MS-LS1-3
Common questions
Why does a cut get red and swollen?
When the skin is cut, the body widens nearby blood vessels and makes them leaky so that extra blood, fluid and white blood cells can reach the wound. This is called inflammation. It causes redness, warmth and swelling, and it is a sign the body is fighting germs and starting repairs.
What do white blood cells do?
White blood cells defend the body against infection. Some, called phagocytes, swallow and digest germs. Others, called lymphocytes, recognise particular invaders and make antibodies or attack infected cells. Some lymphocytes become memory cells that remember a germ for years.
How do vaccines work?
A vaccine shows the immune system a harmless form or piece of a germ. The body learns to recognise it and makes memory cells, without having to suffer the full illness. If the real germ arrives later, the immune system recognises it quickly and fights it off much faster.
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Try it yourself
The Immune Response lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.