Life Comes from Life

Contributor: Felicia Sabur. Lesson ID: 11779

The only thing more disgusting than having flies land on your food is having them lay eggs on it! Centuries ago people thought flies just popped up out of meat. Experiment yourself to show them wrong!


Life Science

learning style
personality style
Grade Level
Middle School (6-8)
Lesson Type
Dig Deeper

Lesson Plan - Get It!


Have you ever wondered why or how those little fruit flies always seem to find their way into your house and directly to the bowl of fruit? Do they just appear out of nowhere?

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.

Before watching the following videos, please 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.)

You will be answering questions as you watch the videos, and writing down your definitions for this lesson's vocabulary:

  • controlled experiment
  • manipulated variable
  • spontaneous generation

Francesco Redi and Spontaneous Generation (


HSCStudyLab: Y12 Biology: Modelling Pasteur's Experiment:


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.

Discuss with your parent or teacher what the manipulated variable was 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 as in the video about Pasteur's experiment. Put on your lab coat and get ready to explore a controlled experiment!


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