evolution. the first cells & their environment environment during time of first cells: no oxygen...
TRANSCRIPT
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
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)