A student repeats Pasteur's idea. She boils broth in four flasks and then treats them in different…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student repeats Pasteur's idea. She boils broth in four flasks and then treats them in different ways.
Flask A is sealed at once. Flask B has a short straight neck that is open to the air. Flask C has a long, curved neck, so the air can enter but the dust is trapped in the bend. In flask D, the curved neck is broken off after some days.
- Which flasks will show living things after a week, if she waits for a long time?
- What does flask C teach, and what does D add?
- What does this result say about spontaneous generation?
Need a reminder? The key ideaShow
The Earth is about billion years old. Chemical evolution came first, then non-cellular life, then cells. Pasteur showed that life comes from life. Miller made amino acids from methane, hydrogen, ammonia and water vapour with an electric discharge. A scale of a clock: billion years.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Flask B, which is open to the air with its dust and germs. Flask D after the neck is broken. Flasks A and C stay clear.
Step 2. (b) Flask C shows that the boiled broth does not make life by itself, even though air can enter. D shows that the broth was able to support life, and that the living things came in with the dust once the trap was gone.
Step 3. (c) Life does not arise from non-living broth again and again. Life today comes from pre-existing life. This ended the idea of spontaneous generation. It did not explain the very first life on the young Earth.
Answer: B and D; C shows that air alone does not make life, and D shows that the germs came with the dust; spontaneous generation was rejected.
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