Zones of inhibition: measure radius and control the comparison
| English | 中文 | Pinyin |
|---|---|---|
| inhibition zone/ɪnhɪˈbɪʃn zəʊn/ | 抑菌圈 | yì jūn quān |
| control disc/kənˈtrəʊl dɪsk/ | 对照纸片 | duì zhào zhǐ piàn |
What would explain this observation?
- A clear circle around a treated disc indicates inhibited growth in that plate. Comparing circle diameters is useful only if the culture and treatment conditions are matched.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- An inhibition zone 抑菌圈 is an area where growth has been prevented or reduced around an applied substance. Its size can reflect the effect on the approved bacterium, but also diffusion through the agar and the dose used. Required practical 2 compares antiseptics or antibiotics using agar plates and measurements of these zones.
- inhibition zone: An area of reduced or absent growth around a treatment in a culture; control disc 对照纸片: A comparison disc without the tested active treatment.
Which value belongs in πr² for a zone of diameter 20 mm?
For a circular region, area = πr². Radius is half the diameter. State whether the reported area includes the disc or subtracts its area: use the same convention for every treatment. A bigger zone does not on its own prove that the substance will treat a particular infection in a person.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- For a circular region, area = πr². Radius is half the diameter. State whether the reported area includes the disc or subtracts its area: use the same convention for every treatment. A bigger zone does not on its own prove that the substance will treat a particular infection in a person.
- Under the school’s supervised microbiological protocol, use equal discs and applied amounts, the same approved organism and agar, matched incubation and a suitable control disc. Keep culture plates closed after incubation. Record repeated diameters through the centre if a zone is not perfectly circular, and explain the approximation.
Which two habits make the investigation or model in this case more defensible?
Under the school’s supervised microbiological protocol, use equal discs and applied amounts, the same approved organism and agar, matched incubation and a suitable control disc. Keep culture plates closed after incubation. Record repeated diameters through the centre if a zone is not perfectly circular, and explain the approximation.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: a zone diameter is 16 mm, giving radius 8 mm. Total circular area = π×8² = 64π, approximately 201 mm². If the disc diameter is 6 mm, its area is 9π, and the clear annulus is 55π, approximately 173 mm². The answer depends on the stated area convention.
A circular zone has radius 5 mm. Using π=3.14, calculate total area. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A circular zone has radius 5 mm. Using π=3.14, calculate total area.
The result is 78.5 mm². Known: a zone diameter is 16 mm, giving radius 8 mm. Total circular area = π×8² = 64π, approximately 201 mm². If the disc diameter is 6 mm, its area is 9π, and the clear annulus is 55π, approximately 173 mm². The answer depends on the stated area convention.
Check the conclusion and its limits
- Do not put the diameter directly into πr². Matched incubation and a control are necessary for interpreting inhibition, and changing both substance and concentration prevents attributing the difference to one variable.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
A larger inhibition zone automatically proves a treatment is suitable for every human infection. This claim is false: Do not put the diameter directly into πr². Matched incubation and a control are necessary for interpreting inhibition, and changing both substance and concentration prevents attributing the difference to one variable.
Zones of inhibition: measure radius and control the comparison: For a circular region, area = πr². Radius is half the diameter. State whether the reported area includes the disc or subtracts its area: use the same convention for every treatment. A bigger zone does not on its own prove that the substance will treat a particular infection in a person.
A larger inhibition zone automatically proves a treatment is suitable for every human infection.
Do not put the diameter directly into πr². Matched incubation and a control are necessary for interpreting inhibition, and changing both substance and concentration prevents attributing the difference to one variable.
An area of reduced or absent growth around a treatment in a culture: write the technical term.
inhibition zone means An area of reduced or absent growth around a treatment in a culture.