Ch 14 Origin of Life Biogenesis All living

Ch. 14 Origin of Life Biogenesis · All living things come from other living things. Prior to seventeenth century, people believed in spontaneous generation. *Living things arise from nonliving things.

Spontaneous Generation n Observation: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times. n Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs.

Spontaneous Generation n Observation: In many parts of Europe, medieval farmers stored grain in barns with thatched roofs (like Shakespeare’s house). As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, and of course there were lots of mice around. n Conclusion: It was obvious to them that the mice came from the moldy grain

2 examples of Spontaneous Generation 1. Maggots arose on spoiled meat. 2. Ponds had fish in them when last year had nothing. People thought fish arose from the mud.

3 Experiments to disprove Spontaneous Generation: 1. Francesco Redi (1668) 2. Lazzaro Spallanzani (1750) 3. Louis Pasteur (1850)

1. Redi’s experiment (mid 1600’s) *He had two jars, one with netting and one with no netting. He put meat into both jars. Flies and maggots were only on control group (jar with no netting). So this proved maggots were from eggs laid by flies so disproved spontaneous generation. Look at p. 261, fig. 14 -1

Redi

2. Spallanzani’s Experiment (early 1700’s) n Wanted to test spontaneous generation of microorganisms. People thought that microorganisms arose from a “vital force” in the air (a force that causes spontaneous generation). They thought this because they saw microorganisms with a microscope but did not know where they came from. So Spallanzani performed an experiment to show this.

Spallanzani n He used 2 flasks of broth. He boiled both to kill all microorganisms present. He then sealed 1 completely tight and left the other one open. The one open grew cloudy and microorganisms were present. The closed one had no microorganisms present. A lot of spontaneous generation believers did not accept this as proof. They said that the “vital force” was also killed. (p. 262 fig. 14 -2).

Spallanzani

3. Pasteur’s Experiment (early 1800’s) *He won a prize given by the Paris Academy of Science. He did something similar to Spallanzani. But Pasteur used curved neck bottles. This prevented microorganisms from entering but still allowed air to be there. 1 year, no microorganisms. He then broke off the neck and next day there was microorganisms. This made the principle of biogenesis a cornerstone in biology. (p. 263 fig 143).

Pasteur