Life Comes From Life

Lesson Plan - Get It!

Audio:

Those little fruit flies are not just spontaneously appearing from fruit.

Infestations can originate from fruits, vegetables, or any organic matter that was previously infested and brought into the home.

The adults can also fly in from outside through windows and doors. They can lay up to 500 eggs, and they are ready to hatch within a week!

Four hundred years ago, many people believed that life could spontaneously appear from non-living things. This idea is known as spontaneous generation.

Two well-known experiments were carried out 200 years apart by Francisco Redi and Louie Pastuer that proved the idea of spontaneous generation was mistaken.

To prove the theory of spontaneous generation untrue, the two scientists conducted controlled experiments.

A controlled experiment is when two tests are identical in every way except for one factor. When carried out simultaneously, the one differing factor that the scientist changes is called the manipulated variable.

Take a moment now to print the Living Things Notebook from Downloadable Resources in the right-hand sidebar, if you haven't done so already. (Work through the first Related Lesson there as well if you have yet to do so.)

As you watch the two videos below, answer the listed questions and write down definitions for the following vocabulary words.

• controlled experiment
• manipulated variable
• spontaneous generation

It was initially believed that spontaneous generation was possible because maggots appeared on rotting meat. Through the experiments of Redi and Pasteur, the theory of spontaneous generation was refuted.

By conducting a controlled experiment, Redi proved that maggots only appeared in the jars of rotting meat left uncovered because the flies were able to lay their tiny eggs on the meat.

Pasteur was able to prove it incorrect by bending the neck of one flask, so bacteria could not enter, and leaving another flask open to the air. When bacteria began to grow in the open flask, he proved that bacteria were everywhere, including in the air.

• What was the manipulated variable in each of the experiments?

In the Got It? section, you will become the scientist. You may perform Redi's experiment, using a banana instead of meat, or you may perform Pasteur's experiment using chicken broth.

Put on your lab coat and get ready to explore a controlled experiment!