Store cultures between periods
Warm to grow, cold to hold, inverted either way. Learn what storage is actually controlling and why a food refrigerator is never the answer.
- Temperature sets how fast things grow: Warmth speeds growth and cold slows it. Storage is mostly a decision about which of those you want right now.
- Water condenses and falls: Moisture leaving warm agar collects on the cooler surface above it, which is why orientation matters in storage as well as in the incubator.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Now separate what belongs in a laboratory store from what does not.
Why is a drink never kept in the same refrigerator as laboratory cultures?
Reviewed- A.The drink would take up room needed for plates
- B.Cold drinks raise the internal temperature when they are put in
- C.It gives a person a reason to reach past open cultures
- D.Refrigerator doors are not opened often enough for drinks to stay cold
Show the worked solution ▾
Answer: C. It gives a person a reason to reach past open cultures
- Step 1: Ask what the rule prevents: Two things: a hand going in and out for a reason unconnected to the work, and something a person will swallow sitting in a space treated as contaminated.
- Step 2: Notice that both are about the person: The hazard is not to the plates. It is to whoever drinks it.
Why it's right: The rule protects the person, not the plates. It removes a reason to reach in among cultures and keeps anything swallowed out of a space treated as contaminated.
- A: Space is a practical annoyance with an easy fix, and it would not justify a rule written into every laboratory's practice.
- B: A drink warms the space very briefly and the unit recovers. Temperature is not what this rule is about.
- D: Door openings affect temperature stability slightly and have nothing to do with why food is excluded.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
A plate comes out of the refrigerator after a weekend. How should it be handled compared with when it went in?
Reviewed- A.With less caution, because cold storage reduces the number of organisms
- B.With less caution, because the growth has stopped changing
- C.With the same caution, because cold slowed it and did not kill it
- D.With more caution, because cold makes organisms more infectious
Show the worked solution ▾
Answer: C. With the same caution, because cold slowed it and did not kill it
- Step 1: Ask what cold did: It slowed the rate at which the organisms multiply.
- Step 2: Ask what it did not do: It did not remove or kill them, so the plate is exactly as live as it was.
Why it's right: Cold slows the rate of multiplication and removes nothing. The plate holds the same living organisms it held on Friday, so it is treated the same way.
- A: Numbers do not fall reliably or predictably in a refrigerator. What cold does dependably is stop them climbing.
- B: A stable culture is still a live one. Whether it is growing does not change what it can do to a person.
- D: Cold does not increase infectivity. This overcorrects in the other direction and still misdescribes what storage does.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
- A student takes stored plates out for the observation lesson and gloves up before touching them.
Fill these in as you work through the lesson.
- Incubate (hold warm so it grows):
- Inverted (agar side up):
- Overgrown (colonies merged, isolation lost):
- Dedicated fridge (for specimens only, never food):
Warm storage makes a culture , cold storage makes it , and either way the plate sits so condensation cannot fall on the agar.
- Explain what happens to an isolation streak that is incubated for too long.
- Give the reason cultures never share a refrigerator with food or drink.
- Say why plates are sealed or bagged in storage.
You streak three plates on a Friday and the next lesson is Monday. Left warm all weekend the colonies merge and the isolation you streaked for is gone. Incubated only until colonies appear and then moved to cold storage, the plate you see on Monday is the plate you made.