Culturing microorganisms: growth and contamination are separate
| English | 中文 | Pinyin |
|---|---|---|
| aseptic technique/æˈseptɪk tekˈniːk/ | 无菌操作 | wú jūn cāo zuò |
| binary fission/ˈbaɪnəri ˈfɪʃn/ | 二分裂 | èr fēn liè |
| antibiotic/ˌæntɪbaɪˈɒtɪk/ | 抗生素 | kàng shēng sù |
| disinfectant/ˌdɪsɪnˈfektənt/ | 消毒剂 | xiāo dú jì |
What would explain this observation?
- An extra organism on an agar plate can change a test result. Aseptic technique 无菌操作 reduces contamination so the effect of the tested substance can be interpreted.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Bacteria divide by binary fission 二分裂. With enough nutrients and suitable temperature, some can divide every twenty minutes, but a supplied mean division time should be used for a particular calculation. They can grow in nutrient broth or form colonies on agar. An uncontaminated culture is needed to compare antibiotic 抗生素 or disinfectant 消毒剂 effects.
- binary fission: Division of a bacterial cell into two cells; aseptic technique: Methods that reduce contamination of a culture; antibiotic: A medicine that kills bacteria or inhibits their growth; disinfectant: A substance used to kill or reduce microorganisms on surfaces.
Why are school cultures generally incubated at 25 °C?
Sterilized dishes and media reduce unwanted microorganisms. Sterilizing an inoculating loop prevents it transferring contaminants. The lid is secured with small pieces of tape rather than sealed all around; the plate is stored upside down to reduce condensation falling onto the agar. School cultures are generally incubated at 25 °C to reduce the chance of growing harmful human pathogens.
Match each technical term to its precise meaning.
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Sterilized dishes and media reduce unwanted microorganisms. Sterilizing an inoculating loop prevents it transferring contaminants. The lid is secured with small pieces of tape rather than sealed all around; the plate is stored upside down to reduce condensation falling onto the agar. School cultures are generally incubated at 25 °C to reduce the chance of growing harmful human pathogens.
- Use only the school’s approved non-pathogenic organism, apparatus and supervised protocol. Students explain the aseptic controls and record labelled plate observations; staff manage approved sterilization and disposal. Do not reopen incubated cultures. Keep organism, medium, temperature and exposure time the same in comparisons.
Which two habits make the investigation or model in this case more defensible?
Use only the school’s approved non-pathogenic organism, apparatus and supervised protocol. Students explain the aseptic controls and record labelled plate observations; staff manage approved sterilization and disposal. Do not reopen incubated cultures. Keep organism, medium, temperature and exposure time the same in comparisons.
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 model starts with 40 bacteria and has a mean division time of 30 min. After 90 min there are three complete divisions. Population = 40×2³ = 320. This ideal model assumes every cell divides on schedule without death or nutrient limitation. In this specification, expressing this culture-growth result in standard form is a Higher-tier extension.
A model starts with 25 bacteria and completes four division rounds. Find its population. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A model starts with 25 bacteria and completes four division rounds. Find its population.
The result is 400 cells. Known: a model starts with 40 bacteria and has a mean division time of 30 min. After 90 min there are three complete divisions. Population = 40×2³ = 320. This ideal model assumes every cell divides on schedule without death or nutrient limitation. In this specification, expressing this culture-growth result in standard form is a Higher-tier extension.
Check the conclusion and its limits
- Twenty minutes is not a universal division time. An apparently clear plate is not proof of sterility, and a contaminated culture cannot be made a fair comparison by ignoring the extra colonies. Practical precautions protect people and the validity of the evidence.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Every bacterial species divides once every twenty minutes under all conditions. This claim is false: Twenty minutes is not a universal division time. An apparently clear plate is not proof of sterility, and a contaminated culture cannot be made a fair comparison by ignoring the extra colonies. Practical precautions protect people and the validity of the evidence.
Culturing microorganisms: growth and contamination are separate: Sterilized dishes and media reduce unwanted microorganisms. Sterilizing an inoculating loop prevents it transferring contaminants. The lid is secured with small pieces of tape rather than sealed all around; the plate is stored upside down to reduce condensation falling onto the agar. School cultures are generally incubated at 25 °C to reduce the chance of growing harmful human pathogens.
Every bacterial species divides once every twenty minutes under all conditions.
Twenty minutes is not a universal division time. An apparently clear plate is not proof of sterility, and a contaminated culture cannot be made a fair comparison by ignoring the extra colonies. Practical precautions protect people and the validity of the evidence.
Division of a bacterial cell into two cells: write the technical term.
binary fission means Division of a bacterial cell into two cells.