Science & Technology in Action

8th Edition

The Science of Sterilisation


Sterilisation is the name given to the process that eliminates or kills all forms of micro-organisms and their spores. This is, in practice, difficult to achieve. This lesson explains why the methods used depend on the material being sterilised and on the type of organisms present.

Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

Until the middle of the 19th century people had no real understanding of the cause of diseases. In general they blamed Miasma [bad air]. However, they did know that having any form of surgery was quite likely to result in death due to sepsis. Sepsis is a severe form of illness in which the body’s immune system cannot overcome an infection and the infection spreads uncontrolled, and often results in death. One of the first people to get an inkling of the cause was Ignaz Semmelweis, a Hungarian physician, who showed that washing hands with a solution of chlorinated lime [Calcium hypochlorite, Ca(OCl)2] before delivering a baby greatly reduced the incidence of childbed fever. Compounds such as chlorinated lime are now called antiseptics because they prevent sepsis.

Semmelweis’s ideas were not widely accepted, due to the general ignorance of doctors, despite his production of scientific evidence.

After reading a paper by Louis Pasteur, that suggested that microorganisms were responsible for gangrene and that these could be eliminated by filtration, heat and chemical solutions, Joseph Lister discovered that spraying a wound, washing hands and surgical instruments with 5% carbolic acid virtually eliminated post-operative infection. He carried out experiments that supported this hypothesis and he published his findings in “The Lancet” [a medical journal] in 1867. His ideas were accepted because they were supported by scientific explanations and because the idea that micro-organisms caused disease was...


Quiz questions

  1. Cooking food sterilises it. false
  2. Gamma rays sterilise food but do not make it radioactive. true
  3. Pasteurisation kills pathogenic bacteria. true
  4. Washing your hands with the sterilising agent at the doors of hospitals makes them sterile. false
  5. UV radiation is really only suitable for surface sterilisation. true
  6. Agar plates should be soaked in bleach before being disposed of. true
  7. Radiation damages DNA. false
  8. Ignaz Semmelweis had no evidence to back up his claim that washing hands before examining a patient saved lives. false
  9. Viruses and prions are living organisms. true
  10. Nano-particles have a role to play in reducing infections in hospitals. true
  11. Lister discovered the first antiseptic. true
  12. Pasteur discovered that heat kills micro-organisms. true
  13. Romans knew about micro-organisms and, because of this, heated blades in a fire before carrying out operations to reduce post-operative infections. false
  14. Ozone is a good sterilising agent. true

Glossary of terms

are powerful medicines that fight bacterial infections.
agent that kills or inhibits the growth of microorganisms on the external surfaces of the body
is the state of being free from disease-causing contaminants (such as bacteria, viruses, fungi, and parasites) or, preventing contact with microorganisms.
aseptic technique
refers to a procedure that is performed under sterile conditions.
is a device used to sterilize equipment and supplies by subjecting them to high pressure saturated steam at 121 °C for around 15–20 minutes depending on the size of the load and the contents.