louis pasteur experiment worksheet

3.1 Spontaneous Generation

Learning objectives.

By the end of this section, you will be able to:

• Explain the theory of spontaneous generation and why people once accepted it as an explanation for the existence of certain types of organisms
• Explain how certain individuals (van Helmont, Redi, Needham, Spallanzani, and Pasteur) tried to prove or disprove spontaneous generation

Clinical Focus

Barbara is a 19-year-old college student living in the dormitory. In January, she came down with a sore throat, headache, mild fever, chills, and a violent but unproductive (i.e., no mucus) cough. To treat these symptoms, Barbara began taking an over-the-counter cold medication, which did not seem to work. In fact, over the next few days, while some of Barbara’s symptoms began to resolve, her cough and fever persisted, and she felt very tired and weak.

• What types of respiratory disease may be responsible?

Jump to the next Clinical Focus box

Humans have been asking for millennia: Where does new life come from? Religion, philosophy, and science have all wrestled with this question. One of the oldest explanations was the theory of spontaneous generation, which can be traced back to the ancient Greeks and was widely accepted through the Middle Ages.

The Theory of Spontaneous Generation

The Greek philosopher Aristotle (384–322 BC) was one of the earliest recorded scholars to articulate the theory of spontaneous generation , the notion that life can arise from nonliving matter. Aristotle proposed that life arose from nonliving material if the material contained pneuma (“spirit” or “breath”). As evidence, he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water. 1

This theory persisted into the 17th century, when scientists undertook additional experimentation to support or disprove it. By this time, the proponents of the theory cited how frogs simply seem to appear along the muddy banks of the Nile River in Egypt during the annual flooding. Others observed that mice simply appeared among grain stored in barns with thatched roofs. When the roof leaked and the grain molded, mice appeared. Jan Baptista van Helmont , a 17th century Flemish scientist, proposed that mice could arise from rags and wheat kernels left in an open container for 3 weeks. In reality, such habitats provided ideal food sources and shelter for mouse populations to flourish.

However, one of van Helmont’s contemporaries, Italian physician Francesco Redi (1626–1697), performed an experiment in 1668 that was one of the first to refute the idea that maggots (the larvae of flies) spontaneously generate on meat left out in the open air. He predicted that preventing flies from having direct contact with the meat would also prevent the appearance of maggots. Redi left meat in each of six containers ( Figure 3.2 ). Two were open to the air, two were covered with gauze, and two were tightly sealed. His hypothesis was supported when maggots developed in the uncovered jars, but no maggots appeared in either the gauze-covered or the tightly sealed jars. He concluded that maggots could only form when flies were allowed to lay eggs in the meat, and that the maggots were the offspring of flies, not the product of spontaneous generation.

In 1745, John Needham (1713–1781) published a report of his own experiments, in which he briefly boiled broth infused with plant or animal matter, hoping to kill all preexisting microbes. 2 He then sealed the flasks. After a few days, Needham observed that the broth had become cloudy and a single drop contained numerous microscopic creatures. He argued that the new microbes must have arisen spontaneously. In reality, however, he likely did not boil the broth enough to kill all preexisting microbes.

Lazzaro Spallanzani (1729–1799) did not agree with Needham’s conclusions, however, and performed hundreds of carefully executed experiments using heated broth. 3 As in Needham’s experiment, broth in sealed jars and unsealed jars was infused with plant and animal matter. Spallanzani’s results contradicted the findings of Needham: Heated but sealed flasks remained clear, without any signs of spontaneous growth, unless the flasks were subsequently opened to the air. This suggested that microbes were introduced into these flasks from the air. In response to Spallanzani’s findings, Needham argued that life originates from a “life force” that was destroyed during Spallanzani’s extended boiling. Any subsequent sealing of the flasks then prevented new life force from entering and causing spontaneous generation ( Figure 3.3 ).

Check Your Understanding

• Describe the theory of spontaneous generation and some of the arguments used to support it.
• Explain how the experiments of Redi and Spallanzani challenged the theory of spontaneous generation.

Disproving Spontaneous Generation

The debate over spontaneous generation continued well into the 19th century, with scientists serving as proponents of both sides. To settle the debate, the Paris Academy of Sciences offered a prize for resolution of the problem. Louis Pasteur , a prominent French chemist who had been studying microbial fermentation and the causes of wine spoilage, accepted the challenge. In 1858, Pasteur filtered air through a gun-cotton filter and, upon microscopic examination of the cotton, found it full of microorganisms, suggesting that the exposure of a broth to air was not introducing a “life force” to the broth but rather airborne microorganisms.

Later, Pasteur made a series of flasks with long, twisted necks (“swan-neck” flasks), in which he boiled broth to sterilize it ( Figure 3.4 ). His design allowed air inside the flasks to be exchanged with air from the outside, but prevented the introduction of any airborne microorganisms, which would get caught in the twists and bends of the flasks’ necks. If a life force besides the airborne microorganisms were responsible for microbial growth within the sterilized flasks, it would have access to the broth, whereas the microorganisms would not. He correctly predicted that sterilized broth in his swan-neck flasks would remain sterile as long as the swan necks remained intact. However, should the necks be broken, microorganisms would be introduced, contaminating the flasks and allowing microbial growth within the broth.

Pasteur’s set of experiments irrefutably disproved the theory of spontaneous generation and earned him the prestigious Alhumbert Prize from the Paris Academy of Sciences in 1862. In a subsequent lecture in 1864, Pasteur articulated “ Omne vivum ex vivo ” (“Life only comes from life”). In this lecture, Pasteur recounted his famous swan-neck flask experiment, stating that “…life is a germ and a germ is life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment.” 4 To Pasteur’s credit, it never has.

• How did Pasteur’s experimental design allow air, but not microbes, to enter, and why was this important?
• What was the control group in Pasteur’s experiment and what did it show?
• 1 K. Zwier. “Aristotle on Spontaneous Generation.” http://www.sju.edu/int/academics/cas/resources/gppc/pdf/Karen%20R.%20Zwier.pdf
• 2 E. Capanna. “Lazzaro Spallanzani: At the Roots of Modern Biology.” Journal of Experimental Zoology 285 no. 3 (1999):178–196.
• 3 R. Mancini, M. Nigro, G. Ippolito. “Lazzaro Spallanzani and His Refutation of the Theory of Spontaneous Generation.” Le Infezioni in Medicina 15 no. 3 (2007):199–206.
• 4 R. Vallery-Radot. The Life of Pasteur , trans. R.L. Devonshire. New York: McClure, Phillips and Co, 1902, 1:142.

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Access for free at https://openstax.org/books/microbiology/pages/1-introduction

• Authors: Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster
• Publisher/website: OpenStax
• Book title: Microbiology
• Publication date: Nov 1, 2016
• Location: Houston, Texas
• Book URL: https://openstax.org/books/microbiology/pages/1-introduction
• Section URL: https://openstax.org/books/microbiology/pages/3-1-spontaneous-generation

© Jul 18, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.

Incorporate STEM journalism in your classroom

• Exercise type: Activity
• Topic: Microbes

Fermentation and Pasteurization in the classroom

• Download Student Worksheet

Purpose: Students will learn about pasteurization by performing an experiment that involves calculating and interpreting results.

Over 6,200 homeschool resources and growing!

FREE Printables and Resources About Louis Pasteur

Published: March 25, 2020

Contributor: Sarah Shelton

Disclosure: This post may contain affiliate links, meaning if you decide to make a purchase via my links, I may earn a commission at no additional cost to you. See my disclosure for more info.

When I think of scientist Louis Pasteur,  the first thing that comes to mind is the word pasteurization. That’s because Pasteur was the famous scientist who created pasteurization. This process helped to make milk safe to drink and dairy products safe to eat and to last longer. This method is currently used today to keep our food safe from germs. He also created important vaccines, and different fermentation techniques.

[series_meta]

Louis Pasteur was the first scientist who discovered that microbes existed in the air around us. Pasteur was a famous pioneer whose studies created the foundation for our modern day understanding of the theory of germs. He laid the ground work for future scientists to study the theory of germs and vaccine development against diseases. 

Biography of Louis Pasteur:

Pasteur was born in 1822 in France. He was a French chemist and microbiologist. He discovered that heating up liquids and allowing them to cool would kill bacteria, thus pasteurization was born. His work in the theory of germs also allowed him to come up with vaccinations for anthrax and rabies. He was a great scientist who contributed so much to our health and safety in the world. His practices are still being used today. He died in Paris, France in 1895.

You can read more on the biography of his entire life and his discoveries and creations at Biography.com .

Learn about Louis Pasteur and all of his contributions to science with scientific diagrams and pictures at Famous Scientists .

Pasteur Biography for Kids – Ducksters.com

Louis Pasteur Facts for Kids – Kids Kiddle

If you are wanting your kids to learn about this famous scientist you will enjoy these FREE Printables and Resources About Louis Pasteur.

FREE Printables and Resources About Louis Pasteur:

Pasteur Facts, Quotes and Information on Germs – Science Kids

Louis Pasteur Timeline Poster and Printables – SparkleBox

Lessons for Kids on Louis Pasteur – Study.com

Louis Pasteur Notebooking Page – Homeschool Helper Online

Louis Pasteur Worksheet – Education.com

Printable Biography and Reading Lesson with Activities on Louis Pasteur – Teacher Vision

Historical Profile of Louis Pasteur with different articles and photographs – Science History Institute

The Rabies Vaccine Backstory Article – The Scientist

10 Interesting Facts About Louis Pasteur – What Tha Fact

Recommended Resource: Famous People Notebook: Scientists

Explore the life and work of 10 scientists that changed history. Our biographical unit studies include text, comprehension questions, written narration, and answers.

Science Experiments and Projects:

We love using hands-on science experiments and projects in our homeschool. It really makes the material come alive. Textbook science can be so boring to kids. Adding in extra hands-on activities can really help them to grasp and understand the concepts that they are reading about. They are also a lot of fun and can create some sweet memories.

Pasteurization:

Practice Using the Scientific Method with Louis Pasteur – Learning Hypothesis

What is Pasteurization? Learn about the pasteurization of milk – Mocomi.com

Souring Milk for Science – National Agriculture in the Classroom 

Educator Resources for Pasteurization – Brainpop Educators

Pasteurization Lessons for Kids: Definition and Process – Study.com

Making yogurt is a great way to show your kids exactly how to pasteurize something. You can sometimes find lightly pasteurized milk at a health food store, or if you can get raw milk from a local dairy farmer, that’s even better. It’s a lot of fun to slowly heat the milk and watch the temperature change, and then instantly cool it in an ice bath. 

Here are some easy yogurt recipes to try at home with your family:

Easy Homemade Yogurt in the Instant Pot – Raia’s Recipes

How to Make Yogurt in Your Oven – Oh The Things We’ll Make

Easy Crockpot Yogurt – Eating on a Dime

Information about Pasteur’s Germ Theory:

Summary of Louis Pasteur’s Germ Theory of Disease – Biology Wise

Pasteur’s Papers on the Germ Theory – Biotech.Law

Louis Pasteur and the Germ Theory of Disease – STMU History Media

This free printable on germs and safety will help you teach your children about germs and how to fight sickness:

Fighting Sickness Printable Pack and Checklist

Sarah Shelton

Sarah is a wife, daughter of the King and Mama to 4 children (two homeschool graduates) She is a an eclectic, Charlotte Mason style homeschooler that has been homeschooling for over 20 years.. She is still trying to find the balance between work and keeping a home and gardens. She can only do it by the Grace of God, coffee and green juice

Related resources

Fun Farm Animal Cutouts Printable Cut & Paste Activity

Free Printable Periodic Table Worksheet and Cheat Sheets

Fun Apple Life Cycle Activities for Kids with Free Printable

40+ Fire Safety Printables & Activities for Fire Safety Week

The Best Children’s Encyclopedia Books for Reference

Printable Parts of a Flower Worksheets For Kids

Louis Pasteur Worksheets

In this science worksheet and activity, children delve into the life and contributions of microbiology pioneer Louis Pasteur. They discover how Pasteur's curiosity led him to study bacteria and germs' influence on food safety and human health, leaving a lasting impact on the world. After learning about Pasteur's work, students are encouraged to conduct their own experiments, drawing inspiration from his field of inquiry. It's an engaging way for kids to explore the world of science and appreciate the legacy of this remarkable scientist.

Other similar worksheets

5th Grade Reading Worksheet

Louis pasteur.

Children learn about the life and work of microbiology pioneer Louis Pasteur in this science worksheet and activity. Students read how Pasteur was inspired to investigate bacteria and germs' roles in food safety and human health, and how the impact of his work endures today. Kids then take inspiration from Pasteur's field of inquiry by conducting an experiment of their own.

View aligned standards

Related guided lesson.

Figurative Language

• Skip to primary navigation
• Skip to main content
• Skip to primary sidebar
• Skip to footer

KidsKonnect

Reading Comprehension Cause and Effect Context Clues Compare and Contrast

Noun Worksheets Writing Prompts Compound Words Figurative Language

The Wizard of Oz Hans Christian Andersen Types of Writing Text Structure

Literary Devices

Alliteration Hyperbole Metaphor Irony

Subject Verb Agreement Poetry Climax Rhyme

View all reading worksheets

Action Verbs Tragedy Transition Words Phonics

View all writing worksheets

Dramatic Irony Cacophony Anaphora Setting

View all literature worksheets

Abbreviations Transition Words Conclusion Situational Irony

View all literary device worksheets

Women’s History

Inspirational Women Women's History Month First Lady of the US Women's Equality Day International Women's Day

View all Women's History worksheets

American Revolution

American Revolution Patriots & Loyalists Patrick Henry Sons of Liberty

View all American Revolution worksheets

US Constitution US Independence Trail of Tears The Pilgrims

View all US History worksheets

Ancient History

Ancient China Ancient Mayan Ancient Rome Ancient Aztec

View all Ancient History worksheets

World History

Roaring Twenties Industrial Revolution Middle Ages The Renaissance

View all World History worksheets

Famous Wars

World War 1 World War 2 Vietnam War American Civil War

View all Famous War worksheets

Anne Frank Sally Ride Neil Armstrong Christopher Columbus

View all famous figure worksheets

Joe Biden Donald Trump Abraham Lincoln George Washington

View all President worksheets

Roald Dahl Dr Seuss JK Rowling Michael Morpurgo

View all author worksheets

Civil Rights

Rosa Parks Sojourner Truth Medger Evers Martin Luther King

Elvis Presley Johann Sebastian Bach Ella Fitzgerald Wolfgang Mozart

View all musician worksheets

Thomas Edison Albert Einstein Henry Ford Wright Brothers

View all inventor worksheets

Muhammad Ali Michael Jordan Jackie Robinson Jesse Owens

View all athlete worksheets

Nat Turner Ruby Bridges Harriet Tubman Booker T Washington Malcolm X

View all civil rights worksheets

Natural Wonders

River Nile Mount Everest Sahara Desert Mount Etna Ancient Pyramids Amazon River

Landmarks/Sights

Mount Rushmore Statue Of Liberty White House Stonehenge Great Wall of China Santa Fe Trail

New York Texas South Carolina Alaska Nevada Ohio

Australia United Kingdom China Canada Argentina Brazil

Mount Fuji Mississippi River Rocky Mountains Volcano Glacier The Great Barrier Reef

View all natural wonders worksheets

Hoover Dam Bermuda Triangle Leaning Tower Of Pisa Arc De Triomphe Golden Gate Bridge Colosseum

View all landmark worksheets

California Colorado Indiana Florida Washington Georgia

View all US state worksheets

Poland Greece Philippines Japan France India

View all country worksheets

September Topics

Labor Day Constitution Day Autumnal Equinox National Hispanic Heritage Month World War II 9/11 Little Rock Nine Crisis The Great Fire of London Treaty of Paris 1783 Reign of Terror

View all Seasonal worksheets

Social Emotional Learning

Morals and Values Self Management Ethics Depression Relationship Skills Self-Awareneess Self-Esteem Emotions and Feelings Goal-Setting Interpersonal Skills

View all Social-Emotional Learning worksheets

Celebrations

Easter Saint Patrick’s Day Valentines Day Chinese New Year Rosh Hashanah Thanksgiving Flag Day Cinco de Mayo Beginning Of Lent Yom Kippur View all Celebrations worksheets

Remembrance

Pearl Harbor Day Veterans’ Day Memorial Day Battle Of The Somme D-Day 9/11 Anzac Day Martin Luther King Jr. Day International Women’s Day Victoria Day View all Remembrance worksheets

Camels Fox Bears Penguin Wolf Beavers Mountain Lion Red Panda Snow Leopard White Tigers Silverback Gorilla Okapi

View all mammal worksheets

Marine Life

Crabs Starfish Fish Octopus Great White Shark Dolphin Walrus Narwhal Megalodon Shark Killer Whale Beluga Whale Lionfish

View all marine life worksheets

Insects/Invertebrates/Reptiles

Millipede Praying Mantis Ladybug Ants Spider Iguana Chameleon Komodo Dragon Lizard Bearded Dragon Gila Monster Snakes

View all insect worksheets

Eagle Peregrine Falcon Snowy Owl Emu Woodpecker Albatross Swan Quail Bald Eagle Hummingbird Peacock

View all Bird worksheets

Natural World

Avalanche Flood Tsunami Natural Disasters Fossils Ice Age

View all natural world worksheets

Earth Sciences

Water Cycle Global Warming Deciduous Forests Hurricane Sandy Hurricane Katrina Global Warming

View all earth science worksheets

Food Chain Fossils Photosynthesis Cells Ecosystem Plants

View all biology worksheets

Solar System Black Holes Eclipse Stars and Constellations The Moon Comets

View all space worksheets

Chemistry/Physics

Magnetism Graduated Cylinders Solid, Liquid, Gas Gravity Light Sound

View all science worksheets

Kangaroo Horse Bear Lion Lizard Octopus

View all animal worksheets

Addition Sentences Single Digital Addition Two-Digit Addition Three Digit Addition Repeated Addition

View all Addition Worksheets

Ordinal Numbers Cardinal Numbers Rounding Numbers Odd & Even Numbers Comparing Numbers

View all Numbers Worksheets

Counting Money Subtracting Money Change Money Coin Name & Value Calculate Change (Money)

View all Money Worksheets

Number Line Single Digit Subtraction Place Value Subtraction Sentences Input & Output Tables

View all Math Worksheets

Louis Pasteur Facts & Worksheets

Louis pasteur was a chemist known as the “father of microbiology”, search for worksheets.

Download the Louis Pasteur Facts & Worksheets

Click the button below to get instant access to these worksheets for use in the classroom or at a home.

Download This Worksheet

This download is exclusively for KidsKonnect Premium members! To download this worksheet, click the button below to signup (it only takes a minute) and you'll be brought right back to this page to start the download! Sign Me Up

Edit This Worksheet

Editing resources is available exclusively for KidsKonnect Premium members. To edit this worksheet, click the button below to signup (it only takes a minute) and you'll be brought right back to this page to start editing! Sign Up

This worksheet can be edited by Premium members using the free Google Slides online software. Click the Edit button above to get started.

Download This Sample

This sample is exclusively for KidsKonnect members! To download this worksheet, click the button below to signup for free (it only takes a minute) and you'll be brought right back to this page to start the download! Sign Me Up

Table of Contents

A chemist and microbiologist known as the “father of bacteriology” and “father of microbiology.” Louis Pasteur and his prolific career benefitted not only the people of his time but also the people of today.

See the fact file below for more information on Louis Pasteur, or you can download our 27-page Louis Pasteur worksheet pack to utilize within the classroom or home environment.

Key Facts & Information

Early life and education.

• Louis Pasteur was born on December 27, 1882 to parents Jean Joseph Pasteur and Jeanne-Etiennette Roqui in Dole, Jura, France .
• His father, Jean Joseph, was a tanner and a major sergeant. From him, Louis Pasteur learned and imbibed patriotism. 
• Louis Pasteur grew up in a Catholic upbringing, contributing to his strong faith in God.
• He attended primary school in Arbois and secondary school in Besancon. As a student, Louis Pasteur was average but gifted in painting and drawing.

CAREER AND CONTRIBUTIONS

• Louis Pasteur earned his master’s degree and a doctorate degree in 1845 and 1847, respectively, at the École Normale Supérieure.
• After finishing his doctorate degree and while waiting for his appointment, Louis Pasteur studied the ability of certain crystals to exhibit optical activity. 
• He was able to demonstrate that optical activity has a relationship with the shape of the crystals of a compound. 
• He was able to conclude that there is some internal arrangement in a compound that allows them to twist the light. This discovery holds importance in the early history of structural chemistry.
• In 1848, Louis Pasteur was appointed professor of physics in a secondary school. Later on, he was appointed as a chemistry professor at the University of Strasbourg.
• In 1849, he married Marie Laurent, the daughter of the University Rector. They had five children but only two survived childhood. Three of his children died due to typhoid fever which made him study infectious diseases.
• In 1854, Louis Pasteur was appointed professor of chemistry and dean of the Faculty of Sciences at the University of Lille. This is where he began his studies in fermentation. 
• He was asked to help solve problems involving beer and wine manufacturing. This was the start of his series of studies on alcoholic fermentation.
• During this time, spontaneous generation was widely accepted. It is a theory that states that living matter can arise from nonliving matter. Only a few, like Pasteur, believed that microorganisms are existing and that they can cause fermentation as well as diseases.  
• Louis Pasteur studied different aspects and types of fermentation.
• This included the production of lactic acid and the fermentation of butyric acid.
• In 1857, Louis Pasteur returned to Paris to serve as the director of scientific studies at the École Normale Supérieure. Here he continued working on fermentation. In the same year, he presented pieces of evidence showing the participation of living organisms in the process of fermentation. Also, how a specific organism causes a certain type of fermentation. This came to be the Germ Theory of Fermentation. Furthermore, he proposed that putrefaction is due to specific germs that can only operate in the absence of oxygen.
• This process is known as the Pasteur Effect. This also gave rise to the understanding that organisms can either be aerobic or anaerobic. Aerobic organisms live in the presence of oxygen while anaerobic organisms live in the absence of it.
• In 1863, at the request of Napoleon III, Pasteur studied wine and the possible causes of contamination.
• He found out that microbes are the cause of contamination. He devised a simple process to prevent contamination. By simply heating the wine to temperatures less than 100 C, microbes that cause contamination are killed. This process is known as pasteurization.
• These days, pasteurization is no longer used for wines that benefit from the aging process, as it kills the microorganisms that contribute to aging.
• Aside from wine, Pasteur also contributed to the beer industry by devising a method that can prevent the deterioration of the product during transportation.
• Since 1861, Pasteur has been conducting studies that disprove spontaneous generation. Many scientists believed in this theory, that life can arise from nonliving matter. Only a handful of scientists during this time did not believe in this theory, this, of course, includes Louis Pasteur.
• He used a simple experiment to combat this belief. Using a “swan-neck” flask, he demonstrated how beef broth can be sterilized by preventing dust particles and other contaminants from reaching the broth.
• A “swan-neck” flask has a long bending neck that prevents contaminants from entering the body of the flask by trapping them in the neck.
• He also showed that if the “swan-neck” flask was tipped to allow contaminants to come in contact with the broth, microbial growth will occur. Same as if the neck of the flask is broken.
• These experiments disproved spontaneous generation. Moreover, this became the foundation of bacteriology. Pasteur’s observations and findings also lead to the antisepsis system of Lister, and now asepsis and sterilization.
• In 1862, Pasteur was elected to the Académie des Sciences and in 1863, he was appointed professor of geology, physics, and chemistry at the School of Fine Arts.
• He then placed his attention and efforts on saving the silk industry of France. In the middle of the 19th century, silkworm eggs could no longer be produced in France, and by 1865, the silkworm industry in France was almost ruined.
• Upon the request of his former professor, Dumas, Pasteur accepted the challenge. He took this opportunity to learn more about infectious diseases. In his five years of research, Louis Pasteur became an expert silkworm breeder and identified the cause of the disease.
• He developed a method to prevent the contamination of silkworm eggs by disease-causing organisms. Up to this day, this method is still in use in the silk industry.
• Through his research with silkworms, Pasteur came to realize that each silkworm reacts differently to the disease depending on factors such as physiological and environmental. This became useful to Pasteur when he studied animal and human diseases.
• In 1879, Pasteur made his first discovery in the field of vaccination. He observed that chickens injected with old cholera cultures did not get sick or did not die.
• To further strengthen his observations and hypothesis, Pasteur inoculated two chickens with a fresh virulent strain of cholera. One chicken was previously inoculated with the old or attenuated culture while the other was not.
• The chicken inoculated with the attenuated culture remained healthy while the other died. This principle was applied to many other diseases and resulted in the discovery of vaccines for anthrax and rabies.
• The success of his anthrax vaccine led him to focus on the microbial origin of diseases. His rabies vaccine was also met with great success. These events lead to the international fund-raising campaign to build the Pasteur Institute in Paris which was inaugurated on November 14, 1888. 

LATER LIFE, DEATH, AND LEGACY

• Pasteur had an immense contribution to the field of science and medicine. He was given honors and awards throughout his lifetime.
• Despite this, he did not have enough time to explore all the practical aspects of his theories. 
• One of these is the variability in virulence which is still relevant in the study of infectious diseases today.
• Pasteur’s 70th birthday was celebrated by several prominent scientists including Joseph Lister, the man behind the antisepsis system applied in surgeries.
• Over time Pasteur’s paralysis worsened, and on September 28, 1895, Louis Pasteur died. 
• Aside from the Pasteur Institute founded in 1888, a lot of things including streets, schools, and universities were named after Pasteur.
• Up to this day, we benefit from Pasteur’s discoveries and theories, from pasteurization, and germ theory, to the understanding of vaccination and variability in virulence. Pasteur’s works are in our daily lives and will probably be of help to us until our very last breath.

Louis Pasteur Worksheets

This fantastic bundle includes everything you need to know about Louis Pasteur across 29 in-depth pages. These ready-to-use worksheets are perfect for teaching kids about Louis Pasteur, a scientist known for his significant contributions in microbiology.

Complete List of Included Worksheets

Below is a list of all the worksheets included in this document.

• Louis Pasteur Fact File
• The Life of Pasteur
• Career in Grid
• Pasteur’s Contributions
• Biogenesis vs. Abiogenesis
• Scientific Aptitude
• The Scientific Method
• A Well of Disease
• Mr. Perseverance
• Get Vaccinated!

Frequently Asked Questions

Why is louis pasteur so important.

Louis Pasteur is often remembered as the founder of modern immunology due to his groundbreaking work in the late nineteenth century that catalyzed a greater understanding and appreciation for germ theory. In addition, he helped the optimistic hope that prophylactic vaccination could eliminate all infectious diseases through prophylactic immunization.

How did Pasteur prove germ theory?

In 1861, Pasteur did some studies on germs. He found out that germs could give people diseases. By 1865, Pasteur had more proof that his idea was right. In 1879, he figured out how to make a chicken not get cholera. He did this by making the virus weaker before injecting it into chickens.

How did Louis Pasteur discover vaccines?

In 1885, Pasteur conducted his first-ever human vaccine trial as he researched rabies. Pasteur weakened the virus in rabbits to create this vaccine and then collected it from their spinal cords.

Link/cite this page

If you reference any of the content on this page on your own website, please use the code below to cite this page as the original source.

Link will appear as Louis Pasteur Facts & Worksheets: https://kidskonnect.com - KidsKonnect, January 14, 2023

Use With Any Curriculum

These worksheets have been specifically designed for use with any international curriculum. You can use these worksheets as-is, or edit them using Google Slides to make them more specific to your own student ability levels and curriculum standards.

Related Resources

KidsKonnect is a growing library of high-quality, printable worksheets for teachers and homeschoolers.

Home Facts Privacy About Blog Contact Terms

Safe & Secure

We pride ourselves on being a safe website for both teachers and students. KidsKonnect uses a secure SSL connection to encrypt your data and we only work with trusted payment processors Stripe and PayPal.

The Biology Corner

Biology Teaching Resources

Early Discoveries – CER

Students who are just learning how to do CER’s (claim, evidence, reasoning) often struggle when they are required to develop their own claims and evidence statements.

In this activity, students read stories about historical science, such as Redi’s experiment on meat and maggots and Louis Pasteur’s experiments with the s-shaped flask. The stories are short, about a paragraph long, and include a CLAIM statement and one or two evidence statements. Students are tasked with highlighting the claim statement in green and the evidence statement in yellow. (You could also use colored pencils if students don’t have highlighters. )

Another benefit of this assignment is that it can be used as a way to introduce the characteristics of life. Chapters in the textbook usually start with historical experiments that disproved the idea of spontaneous generation.

Reasoning statements can also be difficult for beginning students. Reasoning is where students must tie the evidence to the claim or link it to established science. In this worksheet, the reasoning statement is started for them, and then they must complete it. For example, ” If water was the cause of the sickness, then … ”

I have a handy CER chart in my classroom that students can refer to, you can download it for free from activatelearning.com

There are two versions of this worksheet. In one version, students must find and highlight the evidence statements. An easier version has statements already underlined, students only then need to identify which is a claim and which is evidence. Reasoning statements in the bee version are multiple choice rather than open ended.

If you download the google doc version, you can add a copy to your own drive and edit it. The answer key available for TpT contains both the regular and bee versions of this handout.

Grade Level: 8-12 Time Required: 15-20 minutes

Shannan Muskopf

Advertisement

How the Scientific Method Works

• Share Content on Facebook
• Share Content on LinkedIn
• Share Content on Flipboard
• Share Content on Reddit
• Share Content via Email

Pasteur's Experiment

The steps of Pasteur's experiment are outlined below:

First, Pasteur prepared a nutrient broth similar to the broth one would use in soup.

Next, he placed equal amounts of the broth into two long-necked flasks. He left one flask with a straight neck. The other he bent to form an "S" shape.

Then he boiled the broth in each flask to kill any living matter in the liquid. The sterile broths were then left to sit, at room temperature and exposed to the air, in their open-mouthed flasks.

After several weeks, Pasteur observed that the broth in the straight-neck flask was discolored and cloudy, while the broth in the curved-neck flask had not changed.

He concluded that germs in the air were able to fall unobstructed down the straight-necked flask and contaminate the broth. The other flask, however, trapped germs in its curved neck,­ preventing them from reaching the broth, which never changed color or became cloudy.

If spontaneous generation had been a real phenomenon, Pasteur argued, the broth in the curved-neck flask would have eventually become reinfected because the germs would have spontaneously generated. But the curved-neck flask never became infected, indicating that the germs could only come from other germs.

Pasteur's experiment has all of the hallmarks of modern scientific inquiry. It begins with a hypothesis and it tests that hypothesis using a carefully controlled experiment. This same process — based on the same logical sequence of steps — has been employed by scientists for nearly 150 years. Over time, these steps have evolved into an idealized methodology that we now know as the scientific method. After several weeks, Pasteur observed that the broth in the straight-neck flask was discolored and cloudy, while the broth in the curved-neck flask had not changed.

Let's look more closely at these steps.

Please copy/paste the following text to properly cite this HowStuffWorks.com article:

Surfing the Net with Kids

Louis Pasteur

December 16, 2008 by Barbara Feldman

Louis Pasteur (1822-1895) was one of the greatest biologists of the nineteenth century. He is credited with the discovery of the germ theory, using heat to kill germs in food products (a process now called pasteurization ), debunking the long held theory of spontaneous generation, and the development of early vaccines to prevent the spread of diseases.

Who was Louis Pasteur?

In this lesson, we will learn about Louis Pasteur's main scientific achievements. We will learn about microorganisms, pasteurisation and vaccines. We will also conduct a scientific investigation to see what conditions mould grows best in.

Switch to our new science teaching resources

Slide decks, worksheets, quizzes and lesson planning guidance designed for your classroom.

Play new resources video

Lesson details

Key learning points.

• Louis Pasteur's life story and contributions to science
• The importance of understanding microorganisms for pasteurisation and vaccines
• Studying the best conditions for growing mould

This content is made available by Oak National Academy Limited and its partners and licensed under Oak’s terms & conditions (Collection 1), except where otherwise stated.

Starter quiz

3 questions, lesson appears in, unit science / extraordinary scientists.

Home » EasyHSC | Australia’s Best HSC Preparation Resources » EasyBio | HSC Biology Studies » Infectious Disease » Causes of Infectious Disease » Investigate the work of Robert Koch and Louis Pasteur

Investigate the work of Robert Koch and Louis Pasteur

Investigate the work of Robert Koch and Louis Pasteur, to explain the causes and transmission of infectious diseases, including:

• Koch’s postulates
• Pasteur’s experiments on microbial contamination

Louis Pasteur:

• Discovered that infectious diseases are caused by micro-organisms. Known as his ‘Germ Theory of Disease’.
• Sought to disprove the theory of spontaneous generation.
• Hypothesized that microbes were in the air everywhere, and food spoils when these microbes land there and become active.
• Poured nutrient broth into 2 identical swan-neck flasks, and boiled both of them to kill of all microbes.
• Then he broke of the necks and left both flasks out in open air.
• As he predicted, the flask with the broth open to the air developed cloudy bacterial growths, while the flask with the swan-neck stayed clear
• This proved that the microbes that spoil food come from the air, and disproved spontaneous generation.
• Pasteur examined samples of fermenting wines under the microscope.
• He observed yeasts, which were converting the sugars to alcohol.
• He also observed bacteria, which were converting sugars to lactic acid.
• The bacteria were also observed in sour milk and were the cause of food spoilage.
• Pasteur showed that heating the wine or milk to 55ºC for a few minutes kills the microbes that spoil them. This process is called pasteurization.

Robert Koch:

• Studied anthrax disease. Anthrax is a bacterial disease that affects sheep and humans.
• Obtained infected matter from a sheep suffering from anthrax
• Placed it on a slide, observed it under a microscope and saw active rod-shaped
• cells and inactive dormant spores.
• Established that the blood of animals with disease always contained these micro-organisms, while the blood of healthy animals did not.
• He found that if blood from an infected animal was injected into a healthy animal, it would cause disease.
• He grew cultures of the rod-shaped bacteria to infect mice – they developed the disease. This proves that it was the bacteria, and not any other blood component that caused the disease.
• The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
• The microorganism must be isolated from a diseased organism and grown in pure culture.
• The cultured microorganism should cause disease when introduced into a healthy organism.
• The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

Extract from HSC Biology Stage 6 Syllabus. © 2017 Board of Studies NSW.

EasyBio > Infectious Disease > Causes of Infectious Disease > Investigate the work of Robert Koch and Louis Pasteur

• Experiment:
• Pasteur and Fermentation:
• Process of his investigation:
• Koch’s Postulates: (for establishing that a certain microbe causes a disease)

Origins of Life I: Early ideas and experiments

by David Warmflash, MD, Nathan H Lents, Ph.D.

Listen to this reading

Did you know that it is much easier to determine when life appeared on Earth than how life came to exist? Evidence points to life on Earth as early as 3.8 billion years ago, but the question of how life came to be has puzzled scientists and philosophers since prehistoric times. In the 1950s, scientists successfully created biological molecules by recreating the atmosphere of primordial Earth in a bottle and shocking it with lightning. This and other experiments give clues to the origins of life.

Theories about the origins of life are as ancient as human culture. Greek thinkers like Anaximander thought life originated with spontaneous generation, the idea that small organisms are spontaneously generated from nonliving matter.

The theory of spontaneous generation was challenged in the 18th and 19th centuries by scientists conducting experiments on the growth of microorganisms. Louis Pasteur, by conducting experiments that showed exposure to fresh air was the cause of microorganism growth, effectively disproved the spontaneous generation theory.

Abiogenesis, the theory that life evolved from nonliving chemical systems, replaced spontaneous generation as the leading theory for the origin of life.

Haldane and Oparin theorized that a "soup" of organic molecules on ancient Earth was the source of life's building blocks. Experiments by Miller and Urey showed that likely conditions on early Earth could create the needed organic molecules for life to appear.

RNA, and through evolutionary processes, DNA and the diversity of life as we know it, likely formed due to chemical reactions among the organic compounds in the "soup" of early Earth.

The work of Darwin and Wallace went a long way in answering the question of how species evolved over time. The theory of natural selection provided a mechanism by which complex life forms, including humans, could arise from simpler organisms . But that still left open a more difficult question, namely, what is the origin of life itself? It’s one of the most challenging questions in science, even today when we can say confidently when life appeared on Earth.

Microscopic fossils called stromatolites and remains of communities of microorganisms called microbial mats suggest that Earth harbored microorganisms 3.5 billion years ago (Figure 1). Also, the presence of particular carbon isotopes in certain metamorphic rocks in Greenland tell scientists that some kind of life may have been present as much as 3.8 billion years ago. This means that 700 million to one billion years after Earth had formed, life was here. It makes sense, because it corresponds to the time when the planet had reached a cool enough temperature for any life to survive. But honing in on the time when life appeared on this planet still does not tell us how life came to exist.

Since prehistoric times, people sought mostly spiritual answers to this question. Around campfires during the Stone Age, each budding culture told and retold tales of how the gods created life from some kind of nonliving material, be it mud, clay, rock, or straw. The details of the ancient creation stories changed noticeably over time, but religion was still the mode of thinking by Darwin’s era when it came to the initiation of life itself. Darwin did consider the origin of life and speculated that it had occurred in a warm pond. He suggested that phosphoric salts and ammonia in the pre-biotic pond somehow had been changed chemically by heat , light , and electricity, leading to the synthesis of the organic compounds needed to produce the first living cells . Darwin was not a chemist and this was a very cursory speculation about Earth’s pre-biotic chemistry. It contrasted sharply with the detail and systematic approach of Darwin’s own theory of natural selection .

Even so, the pond idea was a start. Despite living in a society that almost universally assumed Earth had an intelligent creator, scientists in Darwin’s time were already comfortable with and accustomed to considering the possibility of life getting started without intervention from the gods. The idea was called spontaneous generation and, while it was already very well established by Darwin’s time, it dates all the way back to the time of the ancient Greeks.

• Early thinkers

About 2,600 years ago, in the Ionian city of Miletus (Figure 2), the natural philosopher Anaximander (c. 610–546 BCE) pondered how human babies were born utterly helpless. Without their parents , young humans had no chance to survive and the state of helplessness continued for years. That reality made for a dilemma when considering the first generation of humans, which, Anaximander assumed, must have begun as infants. To grow up and have their own babies, human ancestors in the very distant past must have been more independent as newborns, Anaximander reasoned. They must have been more like certain other animals whose young are born ready to survive on their own.

Considering the various animals, Anaximander decided the ancestors of humans had to be fish. Unlike mammals, which needed their mothers to get started in life, fish simply emerge from their eggs and either die or survive. This means that distant human ancestors could survive as infants if they were more like fish than like humans.

Even in Anaximander’s time, people saw skeletons from long-dead creatures. Fossils of extinct life were found long before paleontologists went looking for them. Ancient Greeks lived by the sea, and often the sea washed up skeletons or eroded the ground to expose buried bones. Living in this environment , Anaximander had a general idea of skeletal anatomy and how it was similar and different between humans and other animals. Because of this, he decided that the transition from fish to humans must have been gradual. In other words, humans descended from fish through an evolutionary process .

Since Anaximander proposed no idea of how the apparent evolution from fish to human had taken place, it was not an early form of Darwin’s theory of natural selection . But it was the beginning of thinking that life on Earth began with small organisms . Anaximander’s idea quickly led to the idea that small organisms were generated through a natural process from nonliving matter , such as the mud at the bottom of the sea.

Over the next centuries, Greek thinkers such as Anaximenes (588–524 BCE), Xenophanes (576–480), Empedocles (495–435), Democritus (460–370), and finally Aristotle (384–322) developed and modified the spontaneous generation idea so that it corresponded to what people often observed on land. Farmers leaving grain in an open container noticed that pretty soon mice appeared, as if the grain generated the mice. People leaving meat untended returned to find maggots infesting the meat, as if the meat generated the maggots.

Comprehension Checkpoint

Testing spontaneous generation

By the 18 th and 19 th century, the older Greek idea of spontaneous generation was well ingrained in the minds of everyone who ventured to think that the origin of life might not have required the gods. And living at a time when science was coming to age, some early modern thinkers started treating spontaneous generation less like a philosophy and more like a scientific hypothesis . Gradually, they began subjecting the idea to scientific experimentation.

An early attempt at testing spontaneous generation occurred in the 17 th century, when the Italian scientist Francesco Redi (c. 1626–1697) looked carefully at the meat-maggot phenomenon. After leaving meat in an open jar, he observed that maggots did indeed appear, and that the maggots then developed into flies, which then flew away. However, when he left meat in a sealed jar, the maggots did not appear. Nor did maggots appear when he left the meat in a jar covered with a mesh screen, a precaution he took just in case spontaneous generation required fresh air for some reason. In the terminology of today’s science, we say that the mesh-covered jar “controlled for” the possibility that spontaneous generation required fresh air (Figure 3).

Since the mesh cover prevented the appearance of maggots, it meant that the maggots were not coming from spontaneous generation , but simply from eggs of adult flies. By the standards of experimental methods in contemporary science, it was a rudimentary experiment , but it was as good as it could be given the equipment available in Redi’s time.

Despite the result of his maggot experiment , Redi still believed that smaller creatures, called “gall insects” came from spontaneous generation . At the same time, a developing invention, the microscope, allowed scientists to focus on creatures even smaller: microorganisms. Using his microscope, an English experimenter, John Needham, noticed that broths made from meat were teeming with microorganisms, so he put spontaneous generation to his own test (see our module Experimentation in Scientific Research ). Needham heated a bottle of broth to kill any microorganisms, and left the bottle for a few days. Then, he looked at the broth under the microscope and found that, despite the earlier heating, the broth contained microorganisms again (Figure 4a).

In Needham’s mind, this finding suggested that the lifeless broth had given rise to life. But another scientist, an Italian named Lazzaro Spallanzani , thought that Needham must have done something wrong. Perhaps, he hadn’t heated the broth to a high enough temperature or for a long enough time. To find out, Spallanzani performed his own experiment . He boiled broth in two bottles, left one bottle open and one closed, and found that new microorganisms appeared only in the open bottle. His conclusion: the microorganisms entered the bottle through the air; they were not generated spontaneously in the broth (Figure 4b).

Experiments seeming to prove or disprove spontaneous generation of life went on for another century. Because of the difference between closed and open vessels, arguments focused on the possibility that spontaneous generation of life might require fresh air. Thus, lack of air in Spallanzani’s closed bottle could have been a factor confusing the results. This possibility attracted the attention of the 19 th century’s most famous microbiologist: Darwin’s contemporary, Louis Pasteur .

Pasteur was drawn to the issue, but once involved he knew he that needed to control for the possibility that air was needed to generate life from nonliving matter . To do this, he designed flasks with long, specially curved, swanlike necks. This allowed sterilized broth to be exposed to fresh air from the outside, but any microorganisms from the air would be trapped in a pool of water in the neck. (See our module Experimentation in Scientific Research for more information on designing experiments .)

The sterilized broths in Pasteur’s special flasks did not become infested with microorganisms despite being exposed to fresh air (Figure 5). And so, after a run of more than 24 centuries, the hypothesis of spontaneous generation was finally laid to rest.

This meant that scientists no longer thought that microorganisms, or small animals, could suddenly emerge with no parents , but it didn’t stop people from thinking about life coming from nonliving matter . Pasteur’s publication of his experimental results disproving spontaneous generation of microorganisms came in the very same year as Darwin’s Origin of Species . This made for paradox. Around the world, scientists were fairly certain that evolution really happened, that all modern species came ultimately from pre-existing, living forms. However, as for the question of how life started in the first place, scientists had just disproved the only explanation they had.

Darwin’s pond idea was completely speculative. There was no way to test it the way he tested natural selection through years of observation of numerous species . And so, when it came to the initiation of life itself, scientists of Darwin’s era were stumped. All they could do was to throw up their hands, or chalk it up to the creation stories of their religions.

• Old and new ideas

In addition to spontaneous generation , the ancient Greeks produced another idea for the origin of life on Earth: panspermia . An Ionian Greek named Anaxagoras (510–428 BCE) thought that life arrived on Earth as seedlings that came through space from other worlds. Often people think of panspermia as an alternative to the idea of life emerging from nonliving matter , but it’s actually not. Instead, panspermia only moves the origin of life off the Earth to another planet or moon, and further back in time. Thus, after Pasteur’s disproval of spontaneous generation , the motivation was stronger than ever to determine how life got started.

By the late 19th century, English biologist Thomas Henry Huxley (1825–1895) coined the term abiogenesis to describe life forms emerging from non-living chemical systems . On first hearing the term, it may sound as if abiogenesis is merely a more modern take on spontaneous generation , but there is a major difference. With spontaneous generation , the idea was that certain materials, be it meat, grain, or mud, were capable of constantly producing some kind of creature. What Huxley had in mind was the chemical reactions of life slowly emerging on the early Earth over a long period of time. Huxley knew that the mixture would have to be more complex than Darwin’s ammonia and phosphoric salts , but he did not attempt to work out the details. Somehow, though, he thought an optimal mixture of simple chemicals generated the complex chemicals needed for life, such as enzymes , and the earliest living cells .

• Abiogenesis

As for how abiogenesis could occur on the primordial Earth, serious thinking about this began in the 1920s with two scientists working entirely independently of one another.

In 1922, Aleksandr Oparin, a Russian biochemist, gave a lecture on the origins of life, which was published as a booklet in 1924. For several years, the booklet was not translated from Oparin’s native Russian, so his ideas were unknown outside of the USSR. Meanwhile, British biochemist John Burdon Sanderson Haldane (usually known by his initials JBS Haldane) was working on similar ideas. Unlike his Russian counterpart, Haldane and his work were extremely visible. He was a great popularizer of science, doing for the early 20th century what astronomer Carl Sagan did later, making science understandable and fascinating for the masses. Haldane’s hands were in numerous areas of life science. He was the author of dozens of scientific papers and spent a great deal of time explaining his work and its importance to people outside the scientific world.

In connection with other questions of biology, Haldane was working with enzymes , which he thought were on the border between living and nonliving chemistry. Consequently, he hypothesized that abiogenesis took place through a complex mechanism involving enzymes and viruses. By Haldane’s time, scientists figured out that the atmosphere of the primordial Earth had been a reduced atmosphere. This means that it contained reduced carbon chemical compounds , such as methane, in contrast to oxidized chemical compounds, such as carbon dioxide (which could be present, but in much lower quantities compared with methane). It also contained hydrogen, ammonia, some water vapor, and, importantly, no oxygen.

Oxygen can come only from organisms that carry out photosynthesis to make their own food. Such organisms are called autotrophs. Haldane reasoned that the first cells must have been heterotrophs, organisms that take their food from the surrounding environment . Methane is a gas , but other simple, organic compounds made from it are liquid and would have rained down on the early Earth. They accumulated as pools of liquid on the surface , forming a kind of organic broth that became known as “Haldane’s soup” (Figure 6).

Because there was no oxygen in the atmosphere , the early Earth lacked a layer of ozone to block out powerful ultraviolet radiation from space. Haldane hypothesized that the ultraviolet radiation from space, along with lightning constantly hitting the primordial organic soup, delivered energy to the various simple organic compounds . This caused chemical bonds between the atoms of the molecules to break and reform, creating new and different molecules, leading to extremely large, complex organic molecules . Haldane speculated that this happened over millions of years, until finally a molecule arose that could copy itself crudely using other molecules in the “soup” as building blocks.

Molecules that could copy better than their neighbors multiplied and gradually dominated the soup. Some of these self-copying molecules became surrounded by a kind of barrier, the precursor to what we call a membrane . This happened by accident, so it was very rare, but when it did happen, Haldane explained, the enclosed, self-copying molecules had an enormous survival advantage. So they came to dominate, ate up the soup, and life had begun.

Haldane’s idea was purely hypothetical. No one tested it yet, but it was far more elaborate than Darwin’s phosphoric salt idea. Moreover, it was perfectly consistent with the state of science in the 1920s and 30s regarding the chemistry of the early Earth. Then, in 1936, Oparin’s work was finally translated from Russian. It turned out that he was proposing almost the same thing as Haldane, so the idea became known as the Oparin-Haldane hypothesis .

• Putting ancient Earth into the lab

As for testing the Oparin-Haldane hypothesis , that role fell into the hands of a graduate student, Stanley Miller. In the early 1950s, Miller was looking for a thesis project in the Department of Chemistry at the University of Chicago. In 1952, his academic mentor, Professor and Nobel laureate Harold Urey, suggested that he try putting the origins of living molecules to a test. That meant recreating the kind of atmosphere that scientists thought had existed on primordial Earth: hydrogen, methane, ammonia, and water. It also meant providing what Haldane thought set the stage for creating more complicated molecules needed for life: lightning and ultraviolet light .

Once the ancient atmosphere was created and contained in a flask, Miller and Urey exposed the mixture to powerful ultraviolet light . They also put electrodes inside the flask and sent an electric current through the apparatus, creating sparks to simulate lightning, which interacted with the gases in the flask. After several days, they checked the contents of the liquid that accumulated at the bottom of the apparatus (Figure 7). They found that different molecules had been created, including various important biological molecules, such as the amino acids glycine, alanine, and valine. They ran the experiment over and over and, depending on how they changed around the gas mixture, different varieties of amino acids and other biological molecules were created. This showed that it was possible for biologically important molecules to form on a planet under abiotic conditions.

Over the years, as Miller progressed through his career, scientists studying planetary atmospheres and the ancient Earth had second thoughts about Earth’s primordial atmosphere. Perhaps it had not been dominated by methane, hydrogen, and ammonia, and possibly it could have been more oxidized as opposed to reduced. But as theories about the ancient atmosphere were refined, Miller tried variations of his original experiment with the adjusted gas mixtures . Although chemical products changed with each new mixture, in each case they included compounds that were vital to life, such as amino acids , or nitrogenous bases , the building blocks needed to make DNA and RNA . The emerging answer seemed to be that, almost regardless what the precise mixture and conditions were, complex organic molecules would result.

• After the Miller-Urey experiment: Exploring proteins and membranes

While ideas about Earth’s primordial atmosphere were in flux from the 1970s onward, NASA’s exploration of the outer Solar System revealed some amazing things about the moons orbiting Jupiter and Saturn. In particular, the space probes Voyager 1 , Voyager 2 , and Cassini and an atmospheric entry probe to Saturn’s moon Titan called the Huygens probe revealed the exact makeup of Titan’s atmosphere. This inspired other scientists, such as Carl Sagan , to redo Miller’s 1952 experiment with a Titan atmospheric mixture. This too produced important biological compounds . Thus, today, the moon Titan is a prime focus for astrobiology studies in the Solar System. It may have exotic life forms, or it may be a model of how Earth was prior to life.

Several years after the original Miller-Urey experiment , another investigator, Sidney Fox, ran experiments showing that some of the Miller-Urey compounds – the amino acids – could join together to form polymers , bigger molecules known as peptides , or small proteins . This happened when amino acids made through a Miller-Urey mechanism were splashed onto surfaces of clays and other materials, under hot, dry conditions. On the ancient Earth, such conditions would have occurred at the boundary between ancient ponds or seas and ancient land. Given enough time, complex proteins could arise.

Other researchers later found that spheres of lipids (the class of organic molecules that includes fats) also could form under conditions thought to exist on the ancient Earth. This would create a water environment inside the sphere that was separated from the outside. In other words, crude membranes can form spontaneously under the same conditions in which biological compounds like amino acids and small proteins can form. The fact that membranes can form spontaneously is key to origins of life research . This is because to move from non-living chemistry to biology, very complex networks of chemical reactions need to emerge. Like a car being made on an assembly line, biological molecules are put together section by section. They also are converted into different molecules section by section, so there is a series of intermediate chemicals in addition to a starting molecule (called a substrate) and final product of each reaction .

In an open environment like Haldane’s primordial soup, or in an ocean, the various intermediates would simply diffuse away before the chemical pathway had a chance to evolve. But a membrane would enclose all of the chemicals within a compartment. That compartment would then act as a chemical laboratory, holding inside any reactions that happened to emerge. Since we know that membrane spheres can spontaneously form, the primordial soup of early Earth must have had billions of these little chemical laboratories in which the chemistry of life was sputtering along.

• Moving to a DNA world

Demonstration that biological molecules and membranes can arise in an abiotic environment is not a demonstration of the emergence of life. It shows only what might have happened in the transition from non-living chemistry to the eventual formation of life. It does, however, show that a necessary step in abiogenesis – the spontaneous emergence of complex organic molecules – is not only possible, but likely under the right conditions.

Theoretically, continuous rearrangement and construction of larger and larger organic molecules from chemical building blocks that would form on the early Earth should eventually lead to molecules that can copy themselves. That’s because the bigger an organic molecule gets, the more functional chemical groups it has. Functional groups are sections of molecules with atoms other than carbon, such as oxygen, nitrogen, and phosphorus, which like to hold onto electrons . This allows for electrons to be moved around between parts of the molecule and between the molecule and other molecules. Also, the bigger a molecule gets, the more it’s able to bend and twist around. This capability, together with the capability to move around a lot of electrons, &^means it’s possible, simply by luck, for any random, very large organic molecule with a lot of nitrogen, oxygen, and phosphorus atoms to have some enzymatic capability –that is, to be able to catalyze chemical reactions .

Certain sets of reactions catalyzed by a molecule can result in the molecule making a copy of itself. Thus, with plenty of building materials in a Haldane soup, as time goes on, it is likely that self-replicating molecules would emerge. The first self-replicating molecule would have only crude copying ability. But, since it would not copy itself exactly, each new “copy” would be a little different than the “parent” molecule. Randomly, a newly copied molecule might have the ability to copy slightly better than the molecule that made it. Natural selection would then work for non-living chemical molecules similar to how Darwin described it working for living organisms . Those molecules copying better would make more copies using building blocks taken from the breakdown of other molecules that could not copy themselves so well.

Self-copying molecules enclosed in membranes would fare even better because they would be held close together with other chemicals. But for life to really begin, there has to have been a molecule whose copying ability was extremely good. Today, there is such a molecule: DNA . However, DNA is incredibly complex and this makes for a chicken and egg kind of dilemma.

In the 1980s, scientists began to realize that not all enzymes are proteins . Scientists dissected some cell components called ribosomes and found that they are made of protein and RNA . What was strange was that some of the RNA molecules actually work as enzymes. They can catalyze chemical changes in themselves and in other RNA molecules.

Like DNA , RNA can hold genetic information, but RNA is less complex than DNA (Figure 8). Consequently, a hypothesis called the “RNA world” was proposed independently by three different researchers: Leslie Orgel, Francis Crick , and Carl Woese. It’s a keystone in origins of life research today. The idea is that RNA emerged on Earth prior to DNA and was the genetic material in the first cells (or in the first cells on a different world, if life began somewhere else).

Today, no known bacterial cell or other fully-fledged life form uses RNA the way that we use DNA , as the storage molecule for genetic information. But there are RNA viruses. Not all viruses are RNA viruses; some use DNA to hold genetic instructions, just as our cells do. But if RNA is adequate as the only genetic material in some viruses, it’s easy to imagine RNA also being the only genetic material in an early bacterium, or other singled-celled creature that could have existed on the early Earth.

It’s not hard to image how the transition from RNA to DNA might have occurred. As with the evolution of everything else, there would have been mistakes. In living organisms today, DNA stores genetic information over the long term and DNA sequences are transcribed into RNA sequences, which then are used to put together sequences of amino acids into proteins (see our Gene Expression: An overview module). Essentially, DNA is an additional layer beyond RNA and the proteins that RNA makes. RNA sequences could have been the genes before a mistake created DNA. Being more stable chemically than RNA, DNA took over the job of storing genetic information. This gave RNA a chance to get better at translating genetic information into proteins.

That would have been an enormous step in life’s evolution . It also would mean that life was not here all at once. Rather, abiogenesis occurred in increments or steps during prebiotic, chemical evolution. Thus, entities must have existed along a spectrum from nonliving to living, just as viruses today have characteristics of both living and nonliving entities. We don’t know the precise abiogenesis pathway, but scientists have worked out each of the major steps necessary to go from nonliving chemistry to self-sustaining cells . Importantly, scientists also have conducted laboratory experiments demonstrating that each step is possible. Unlike the days of Anaximander , Darwin, or even Haldane, there are no big holes or theoretical barriers to abiogenesis. Scientists have a good idea of how it probably happened. Still, in terms of the details within each major step, that is where science is now focused on getting some answers.

Table of Contents

Activate glossary term highlighting to easily identify key terms within the module. Once highlighted, you can click on these terms to view their definitions.

Activate NGSS annotations to easily identify NGSS standards within the module. Once highlighted, you can click on them to view these standards.

Page Loading. Please wait.