Evidence of Spontaneous Generation Maggots developing from rotting meat After spring rain people would observe frogs and insects come to life from the mud of dried up ponds Trees and other plants would automatically grow when nothing was planted
Origins of Life Spontaneous Generation • The idea that organisms originate directly from nonliving matter. • "life from nonlife" • abiogenisis - (a-not bio-life genesis-origin) Biogenesis • The idea that organisms can only be derived from other living organisms
Redi’s Experiment • Redi left some meat out in the open • Within several days maggots appeared on the meat • He then left the maggots and observed that they transformed into hard shelled structures after 20 days. • Further observations showed that these hard shelled structures transformed into flies
Redi (continued) • He remembered seeing flies around the meat prior to the maggots being present • He concluded that the maggots did not spontaneously generate but were an earlier part of the flies’ life.
Redi • To test his new theory Redi placed identical pieces of meat in identical glass flasks and covered one but left the other open. He observed that the open flask produced maggots but the closed flask did not produce maggots.
Redi Experiment # 3 • People did not believe his second experiment because it did on allow air into the flask. • To prove his results he set up three jars this time. One sealed. One open and one with a piece of cloth over the meat. • Maggots developed in the open jar but not on the other two.
John Needham • Designed an experiment to prove that spontaneous generation did exist. • He boiled two containers of broth, sealed one with a cork and left one open. • The boiling was to kill any bacteria or any micro organisms that might be living in the broth • Days later they both turned cloudy with microscopic organisms living in the broth
Lazzaro Spallanzani • Noted some flaws in Needham’s experiment so he did the experiment again but fixed the problems. • First he boiled the broth for an hour rather than 5 – 10 minutes like Needham did. • Second he used different method to seal the flask, instead of a cork he melted the neck shut. • Conclusion – organisms don’t grow in sealed containers
Louis Pasteur • Performed an experiment similar to Spallazani but instead of sealing the container he put an s shaped tube at the top. This allowed air in, but kept air born organisms out of the container. This finally disproved the theory of spontaneous generation and gave rise to the theory of biogenesis. • Biogenesis – all living things must come from living things of the same type
Discovery and Importance of Cells and the Cell Theory • Robert Hooke in 1665 observed a piece of cork under a microscope and called the small empty compartments cells • Felix Dujardin in 1835 concluded that many microorganisms consisted of a single cell • Theodor Schwann in 1838 reported that cells are present in animals • Mathais Schleiden in 1838 found that cells are also present in plants • Combined observations of Schwann ansd Schleiden suggested that all organisms are made of cells
(continued) • Rudolph Circhow in 1858 concluded from his observations of dividing cells that cell can only arise from other cells. • Louis Pasteur in 1861 weakened the theory of spontaneous generation by the experiments he had done
Cell Theory • The cell is the basic unit of organization for all organisms • All organisms are composed of cell or cell products • All cell come from other cells Organisms composed of one cell are called unicellular while those composed of many cells are called multicellular.