The Origin of Life

Last Class

Got to know each other a little better

Reviewed Lab SafetyIntroduced BiologyReviewed the Scientific Method

Objectives

Determine the difference between spontaneous generation and biogenesis

Look at the 3 experiments set out to determine how life comes to beRediSpallanzaniPasteur

Compare the “Electric Spark” theory and the “Panspermia” Theory

Where does life come from?

Think (1m)Pair (1m)Share (3m)

The Theory of Spontaneous Generaton

Dark Ages Hypothesis: Living Organisms could

develop from non-living materialWas this hypothesis proven, or

disproven?

Redi’s ExperimentFrancesco Redi (17th C)Commonly held belief that flies were

developed spontaneously from rotting meat.

Hypothesis: Meat kept away from flies would remain free of maggotsExperimental group: Covered jar

containing meatControl group: Open jar containing

meat

Redi’s Experiment Cont’dAfter a few days, maggots

swarmed over the meat in the open jars, none in the covered jars

Conclusion: Experiment showed that flies only come from eggs laid by other flies

Spallanzani’s Experiment Lazzaro Spallanzani Around the time of the invention of the microscope

World introduced to microorganismsBelieved to be generated from “Vital Force” in

the air Hypothesis: Microorganisms are formed from

other microorganisms, not the air.Experimental Group: Boiled clear, fresh broth until

flask is filled with steam, sealed by melting neck closed.

Control Group: Boiled broth, flask left open

Spallanzani’s Experiment Cont’d Observations: Broth in the sealed flask remained clear, while

broth in open flask became clouded with microorganisms Conclusions: Boiled broth became contaminated only when

microorganisms from the air enter the flask

But of course, there were critics…

Opponents to Spallanzani claimed that he left the flask too hot, thereby boiling away all the life force in the air…

Enter Louis Pasteur

19th Century French BiologistConsidered the Father of MicrobiologyHypothesis: If he used a curved neck

flask that allowed air inside the flask, but solid particles (such as microorganisms) not able to get in flask, then the broth would remain clear

Louis Pasteur’s Experiment Cont’d Broth boiled in experimental curved neck flask remained clear

for up to a year! As soon as curved neck was broken, flasks became

contaminated within a day! Conclusions: Pasteur reasoned that the contamination was

due to microorganisms in the air, not a “life force”. Beginning of the principle of…

BiogenesisThe theory that living organisms

come only from other living organisms

In Your JournalWrite out a journal/diary entry from the

view point of one of these scientistsWhat are your observations on that day?What are you expecting from these

observations?Why are you undertaking this

experiment?

But where did all of this life come from?

Though there is no sure-fire way of knowing where all of life came from, there are several theories.

We will focus onElectric ShockPanspermia

Electric Shock

Start at the beginning of the formation of Earth (~4.5BYA)A condensed mass of orbiting debris consisting of

an iron/nickel core, rock surface and an atmosphere consisting of Hydrogen- H2

Hydrogen Cyanide- HCNMethane- CH4

Water- H2O

Ammonia- NH3

Electric Shock

Earth cools off enough to a point where water can collect in hollow and low region of the Earth to form oceansOcean water is salty due to leeching of

earth materials into the water over a course of billions of years

Electric Shock

While Oceans are forming, molecules of the atmosphere begin to react with one another

Set forth by lightning, heat and radiationH2, HCN, CH4, H2O, NH3 React together

to form organic subunits of life moleculesSugars (Glucose), Glycerine(fats),

Amino Acids (proteins), Nucleotide Bases (RNA/DNA)

Electric Shock

Miller and Urey (1950s)Designed an experiment using the early

atmospheric molecules, and conditions similar to early earth, to see if these organic molecules could arise.

Resulted in formation of the organic molecules responsible for life!

Electric Shock Organic Life molecules began reacting with one another

E.g. amino acid+ amino acid= Proteins Sugar + Sugar= Polysaccharides

These reactions lead to complex molecules known as nucleoproteinsLike all life they were able to reproduce, mutate,

evolve, and needed an energy supply (Nutrition)

Electric ShockEventually these nucleoproteins became protocells

Developed a mechanism to utilize the suns energy for nutrition- Rise of Photosynthesis (Became the autotrophic cells)

Electric Shock and the Oxygen Revolution

Development of Photosynthesis meant that Oxygen was being expelled into the atmosphere as a waste product1. Oxygen in atmosphere began reacting with

each other in the upper atmosphere forming Ozone (O3)- protects life from radiaton

2. The Heteroptrophic cells were now able to utilize O2 in the atmosphere and get more energy Aerobic Respiration

Recap

Atmospheric Gases

Simple Organic

Compounds

Complex Biological Molecules

Nucleo-proteins

Heterotrophic Protocells

Hetero-trophic cells (Animals)

Autotropic cells (Plants)

Panspermia Life exists throughout the universe, distributed

by meteorites, asteroids, comets, planetoid and even space crafts.

Tiny microorganisms from other worlds may be ejected on impact, and travel to other worlds, planting their “life seed”

Some of the earliest microorganisms on our planet are able to survive the most extreme conditions of cold and radiation (similar to the conditions of outer space)

In your Journal What are your thoughts on the origin of life? Did you prefer the Electric Shock or

Panspermia Hypothesis? Explain Do you have any other theories on how life

may have come to be?

Ch14 Review when finished For Interest, research other origin of life

theories. Feel free to share with class next day