Evolution

The First Cells & Their Environment Environment 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’d The 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

Endosymbiosis Eukaryotes differ from Prokaryotes 1. Larger 2. DNA is located in nucleus 3. 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 Life Spontaneous Generation – Before the 17 th century, people believed that living things could come from nonliving things Example: 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 jar Allowed air to enter and prevented flies from landing on meat Results: Maggots seen in jar without netting, but not seen in jar with netting

Needham vs. Spallanzani At 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 Experiment The 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 neck Solid particles (such as other microorganisms) could not

Pasteur’s Experiment: Cont’d Results Broth boiled inside the flask remained clear for one year. After necks were broken off, broth became cloudy and contaminated with microorganisms after one day. Conclusion Microorganisms 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.