Evolution

The First Cells & Their EnvironmentEnvironment during

time of first cells:No oxygen Filled with organic

molecules

Therefore, the first cells were:

Anaerobic (Does not us oxygen)

Prokaryotic (Cells that have no nucleus)

Heterotrophic (Consumers)

The First Cells: Cont’dThe first autotrophs (make their own food)

were believed to use chemosynthesis (does NOT use sunlight)

Around 3 billion years ago, photosynthetic (uses sunlight) life had began

This production of oxygen was start of aerobic respiration (releasing energy using oxygen)

After a long period of time (approx. one billion years) O2 gas levels reached today’s level

EndosymbiosisEukaryotes differ from Prokaryotes

1. Larger2. DNA is located in nucleus3. Have Membrane-bound organelles

Eukaryotes evolved from a mutually beneficial relationship with prokaryotes

Endosymbiosis – Eukaryotic cells engulf prokaryotic cells. Prokaryotic cells then performed beneficial actions inside the eukaryotes while eukaryotes provided a safe environment for the prokaryotes.

This type of relationship allowed for the evolution of complex eukaryotes.

History of LifeSpontaneous Generation – Before the 17th

century, people believed that living things could come from nonliving thingsExample: Rotting meat Maggot

Biogenesis – Living things come from other living things

Redi’s Experiment

Control group – Uncovered jar that contained meat

Experimental group – Netting-covered jarAllowed air to enter and prevented flies from

landing on meatResults: Maggots seen in jar without netting,

but not seen in jar with netting

Needham vs. SpallanzaniAt the time it was accepted that heat was lethal to living organisms

Needham theorized that if he took chicken broth and heated it, all living things in it would die.

After heating the flask and letting it cool, he sealed it

The broth became cloudy with the presence of microorangisms

This proved spontaneous generation for Needham

Spallanzanit performed the same experiment, but did not allow air to enter the heated flask

No microorganisms formed in the broth

However, the finding were rejected because Spallanzani did not allow the “vital force” in the air to enter the flask

Needham’s Experiment

Spallanzani’s Experiment• Spallanzani attempted to refine

Needham’s experiment to disprove spontaneous generation.

• He performed basically the same experiment except with 2 differences: 1) He boiled the broth longer (to kill ALL of the microorganisms) and 2) He immediately capped off one of the containers.

Pasteur’s ExperimentThe invention of microscopes allowed people

to discover microorganisms.People believed these microorganisms

developed spontaneously from the air.Louis Pasteur created an experiment where

broth from boiled meat was placed in a curve-necked flask.Air could enter through the neckSolid particles (such as other microorganisms)

could not

Pasteur’s Experiment: Cont’dResultsBroth boiled inside the flask

remained clear for one year.After necks were broken

off, broth became cloudy and contaminated with microorganisms after one day.

ConclusionMicroorganisms come from

other microorganisms (NO SPONTANEOUS GENERATION)

Each of these experiments played a role in debate of spontaneous generation vs. biogenesis (all life comes from other life).

From these experiments, it was proven that spontaneous generation was false and that biogenesis was true.