History of Life Chapter 14

Biogenesis Biogenesis is the principle that all living things come from other living things Spontaneous generation is the belief that living things arise from non-living things Back in seventeenth century this was the explanation why maggots arise from rotten meat and fish appear in ponds

Francesco Redi Italian scientist ( ) that noticed and described the different forms of flies Observed maggots turned into oval cases and flies emerge Also observed maggots appear where adult flies landed Created an experiment to prove his hypothesis that flies emerge from maggots

Francesco Redi’s Experiment Jars were set up with meat inside and allowed to rot Control group The jars were exposed to the environment and not covered at Experimental group Jars were covered with cloth so air can flow through, but organisms cannot enter or leave

Francesco Redi’s Experiment Results The uncovered jars that were exposed to flies had maggots growing that eventually turned into flies The covered jars did not have any maggots or flies inside

Lazzaro Spallanzani Italian scientist ( ) that used microscopes to observe microorganisms that could explain biogenesis At this time, it was believed that “vital force” was how microorganisms arise from the air Hypothesized that microorganisms formed from pre-existing microorganisms Created an experiment to test his hypothesis

Lazzaro Spallanzani’s Experiment Boiled clear, fresh broth until the flasks filled with steam Control group Flask was remained open during experiment time Experimental group Flask was immediately covered before cooling so not to allow air or bacteria to enter

Lazzaro Spallanzani’s Experiment Results The uncovered flask (control group) became contaminated with microorganisms when air entered The experimental group flask did not have any growth Scientists believed that boiling the broth killed the “vital force” and still continued to believe spontaneous generation

Louis Pasteur French scientist ( ) created an experiment to answer objections of Spallanzani’s experiment Made a curved neck flask that allowed air into the flask, but prevented microorganisms to enter

Louis Pasteur’s Experiment Started the experiment by boiling broth in the curved neck flask to kill any microorganisms inside Left the flask to sit for one year – the broth was still clear After a year, the neck of the flask was broken Results After one day being exposed to the air, the broth became contaminated with microorganisms These results provided evidence for biogenesis and that spontaneous generation was not possible

Formation of Earth Earth’s Age The estimated age of the Earth is 4.5 billion years old Scientists are able to explore the surface and its layers to study its geology and determine age

Formation of Earth Radiometric Dating A method of establishing the age of materials Using isotopes (elements with more or less neutrons) of specific elements, scientists can date the age of rocks and fossils more accurately Mass number = protons + neutrons Isotopes have a different mass number due to change in neutrons Radioactive decay – when isotopes have an unstable nuclei they release energy that we can calculate

Formation of Earth Half-life The length of time it takes for one-half of the same size of the isotope to decay to a stable form Carbon-14 All living things contain the isotope Carbon-14 in their cells As they die, Carbon-14 decays into Carbon-12 at a known rate that scientists can calculate and determine the age of the organism Organisms that are much older, scientists use different isotopes

Alexander Oparin & John Haldane Soviet and American scientists that were able to determine the inorganic compounds found in the early atmosphere They believed it contained Ammonia (NH 3 ) Hydrogen gas (H 2 ) Water vapor (H 2 O) Methane (CH 4 )

Stanley Miller & Harold Urey American scientists that created an experiment to explain how inorganic compounds that existed on Earth created our known atmosphere Set up a chamber containing gases and allowed them to circulate with electric shock Results After going through experiment the end results were organic compounds that make up the modern day atmosphere

Origin of Heredity First cells The oldest known fossils that are thought to be cells are the size and shape of some living bacteria Scientists believe that RNA was the first nucleic acid on Earth Chemosynthesis Archaea – related group of organisms that can survive under harsh conditions Chemosynthesis – when CO 2 serves as the source of energy as well as inorganic molecules like sulfur

Origin of Heredity Photosynthesis & Aerobic Respiration The ability for organisms to use inorganic matter and create oxygen gas Cyanobacteria – most likely the earliest bacteria that created oxygen gas as a byproduct and release it into the atmosphere After billions of years of oxygen gas forming and filling the atmosphere, O atoms reacted with O 2 to form O 3 which is our ozone Without our ozone the UV light from the sun would damage our DNA and life could not have come to exist

The First Eukaryotes Eukaryotes Larger than prokaryotes DNA is organized into chromosomes Contain cytoskeleton and nucleus Endosymbiosis Theory that modern day organelles were engulfed by ancient eukaryotes and later became part of the cell’s function Ex: chloroplast and mitochondria (contain their own DNA)