What is Science? Learning about the natural world.

Science Goals Investigate the natural world. Explain events in the natural world. Use explanations to make predictions.

How do Scientists Work? Question: Have you ever noticed what happens to food left in an open trash can for a few days in the heat?

How Scientists Work For centuries, people have watched maggots appear on old food. Where do they come from?

How Scientists Work In Aristotle’s time (300 BCE), people believed living things came from nonliving things. Maggots arose from meat Mice arose from grain Beetles arose from cow dung

How Scientists Work Belief special “vital” forces gave some nonliving things the opportunity to be alive. Ex: Recipe for Bees Romans thought that you could create bees: 1) kill a bull in winter 2) build a shed and put the bull inside with branches and herbs until summer

How Do Living Things Come Into Being? For centuries, people believed the explanation that living things “arose” from nonliving things.

How Do Living Things Come Into Being? The scholars of the time named the idea of life arising from nonliving matter spontaneous generation.

Is Spontaneous Generation the Answer? Francesco Redi (1600s) An Italian physician In 1668, he proposed a different idea to explain the appearance of maggots on meat.

Redi’s Experiment Redi placed meat in four jars. He covered two jars with gauze and left the other two jars uncovered.

Redi’s Experiment Redi believed that the flies were laying eggs that were too small to see on the meat. After a few days, the eggs hatched and maggots would appear on the meat. He thought that the covered meat would not have any maggots.

Redi’s Results Uncovered flask = maggots and flies Covered flask = no maggots

Redi’s Conclusion Redi’s experiment confirmed what he thought would happen. His tests showed that the maggots were produced by flies. They also showed that spontaneous generation was not possible.

Another Scientist Tests Francesco Redi’s Findings… Lazzaro Spallanzani (1700s) Another Italian scholar Read about Redi’s experiment and decided to try to get the same results from gravy.

Spallanzani’s Experiment Spallanzani boiled two containers of gravy.

Spallanzani’s Experiment He sealed one jar immediately and left the other jar open. After a few days, he checked the jars.

Spallanzani’s Results The gravy in the open flask was filled with microorganisms (tiny living things). The gravy in the sealed flask did not have any microorganisms.

Spallanzani’s Conclusion Spallanzani concluded that nonliving gravy did not produce living things. He concluded that the microorganisms in the unsealed jar were the offspring of microorganisms that had entered the jar through the air.

Another Scientist Tests Spontaneous Generation… Louis Pasteur (1864) A French scientist Finally found a way to totally disprove the idea of spontaneous generation

Pasteur’s Experiment Pasteur designed a flask that had a long, curved neck. The flask would be open to air, but microorganisms from the air did not make their way through the neck into the flask.

Pasteur’s Experiment Pasteur placed broth in two flasks. He boiled the flasks to kill any microorganisms they might contain. He waited for one entire year to see if any microorganisms were found in the flasks. He did not see any microorganisms in either flask.

Pasteur’s Experiment One year after starting his experiment, Pasteur broke the neck of one of the flasks, allowing dust and air and other particles to enter the broth. What do you think his results were?

Pasteur’s Results

Pasteur’s Conclusion In just one day, the flask was clouded from the growth of microorganisms. His work concluded that all living things come from other living things. His work also caused a major shift in the way scientists viewed living things.

Reflection Frames: Today’s Topic:________________ 1. What did I learn about the topic? 2. What part of the topic made me “think?” 3. What did I enjoy about the topic?