Why is redi's experiment a good example of a controlled experiment

A controlled experiment is when the experimenter can change one variable in the experiment and completely change the results.

Redi experiment involved a closed jar with rotting meat on the inside. He waited for a few days and found no new forms of life in the jar.
He then did the same experiment, but this time he took the lid off the jar. After those few days he found there were maggots in the rotting meat from flies.

This is a great example of a controlled experiment, because he only had to change one variable to completely change the results. In this case that variable was just removing the lid from the jar.

Redi was trying to prove spontaneous generation with his experiment. Although, it failed.

Spontaneous generation: When life forms from non-livings.

Redi disproved spontaneous generation, but proved biogenesis.

Biogenesis: When life comes from other living beings.

He proved biogenesis because the flies had reproduced when the jar was opened.