Previous: Elizabeth Blackburn: Great Minds
Next: The Bacon Hoax & the Next REAL Food Shortage



View count:620,717
Last sync:2023-11-28 02:30
Hank tells us the stories of three experiments in biology that, with creativity and luck, changed science & the world with it in their work to solve the mysteries of the universe.

Like SciShow?
Follow SciShow!

References for this episode can be found in the Google document here:

Scientists work everyday to solve the mysteries of the universe; some don't go their whole careers without solving one freak'in mystery. But, others get lucky, or they get creative, and they find answers by trying stuffs out. In science, we call this experimentation.

So today, we're gonna look at three biological experiments that change the world.

[into music]

 Pasteur's Swan-Neck Flask Experiment (0:26)

Number one, the swan-neck flask experiment.

In 1862, Louis Pasteur set out to prove that living things did not spontaneously come into existence. They had to come from some other living things.

Now, that seems like a no -brainer to us, but at the time, most people believe in spontaneous generation - the idea that some kind of "vital principle" in the air caused life to just arise out of nothing.

Pasteur was interested in the newly discovered life form bacteria, and another scientist, Lazzaro Spallanzani, had just proven that bacteria could be killed by being boiled and, if sealed from the air in a container, would not grow back.

Regardless of Spallanzani's finding though, critics argued that boiling just kills the "vital principle" in the air inside the container.

So, Pasteur invented an apparatus that he called the swan-neck flask. He designed it so that a sterile liquid could be exposed to the air, but no outside particles like dust or bacteria could get past the curve in the flask's neck.

He filled the flash with broth, boiled it, and let it sit. Even though it was exposed to the air, the broth never became contaminated with bacteria, proving that air itself had no vital principle.

As a result, the theory of spontaneous generation, enemy of science, was dead - once and for all.

 Hershey and Chase's Blender Experiment (1:43)

Number two, the blender experiment.

In 1952, geneticist Alfred Hershey and Martha Chase used an ordinary kitchen blender to show that organisms' genetic information is stored in DNA.

At the time, it was thought that this information was kept in the proteins. But, to test this, Hershey and Chase used a virus that infects bacteria, called the bacteriophage, which just consists of a strand of DNA surrounded by a protein shell.

They whipped up two batches of this virus; one that had a radioactive marker in its protein shell, and another that had a marker in its DNA.

Next, they let each batch infects some ordinary E. coli bacteria. Then, they used a blender to separate each batch of viruses from the bacteria that they had infected. 

What they found was that in the first batch, the left over solution contained only the radioactive protein.

This suggests that the viruses had left their shells on the outside of the bacteria, and transferred their DNA inside. 

In the second batch, the radioactive DNA was nowhere to be found, again suggesting that it was now somehow inside the bacteria. And sure enough, when they tested the bacteria, the found that the radioactive virus DNA had been incorporated into the bacterial DNA.

Thus not only showing us that DNA contains genetic information, it also taught us how viruses infect their hosts.

 The Miller-Urey Experiment (2:59)

And finally, number three, the Miller-Urey experiment.

Just a year after Hershey and Chase blew everyone's minds, Harold Urey and student Stanley Miller set out to see if they could recreate the conditions that made life on Earth possible in the first place.

First, they theorized the chemical makeup of Earth's early atmosphere over four billion years ago. 

Then, the mixed those ingredients - methane, ammonia, hydrogen, and water - in a network of flasks connected to a continuous 60,000-volt electrical current.

They found that after a week, most of the ammonia and much of the methane had been replaced with carbon monoxide, nitrogen, and amino acids, the building blocks of proteins and the essential components of life.

Today, scientists are still debating Miller and Urey's results, mostly because they were probably wrong about the chemical condition of early Earth. And because amino acids have since been found on meteorites, suggesting that they could have been introduced to Earth from space.

But, since 1953, scores of scientists have recreated this experiment with different ingredients, and eventually sparked the discipline of prebiotic chemistry, which has become incredibly influential and advancing what we know about the origin of life.

 Ending (4:08)

Thanks for watching this SciShow dose. We hope you feel just a little bit smarter today, and if you wanna keep getting smarter with us, you can go to, and subscribe. If you have any ideas or questions or comments for us, we're on Twitter, Facebook, and, of course, in the comments below. We'll see you next time.