Download - And how we try to figure it out
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Life!
And how we try to figure it out
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Figure 1.2 The hierarchy of biological organization
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Biology
• Define life (good luck!).• How do we know a living thing
when we see one?– list characteristics common to
ALL living things.
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Characteristics of all living things:
1. Made Up of Cells - Organization2. Reproduction3. Based on DNA4. Growth and Development5. Need for Energy6. Response to Environmental Stimuli7. Homeostasis8. Evolution
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What makes Biology a science?
• How do you know science when you see it?– list some characteristics of
science and describe how scientists work.
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Science is…• Objective• Data driven• Experimental• Attempt to find the best possible
naturally occurring explanation for a phenomenon.
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Observations are objective• Observe the familiar actions and
describe them. No talking!• Compare notes with others – how
objective were your observations?• What happens when new observations
don’t fit with the old?• How did observations lead to
hypotheses on life?
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Where does life come from?• At least by Aristotle’s time, people were
concerned with this.• Prevailing theory: Spontaneous
generation or Abiogenesis– Life comes from non-living things.– Based on everyday observations– Aristotle described an “active principle”
that was responsible.
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Abiogenesis examples• Salamanders and frogs come from river
mud.• Mice come from wheat that has been
exposed to sweat.• Humans???
– pregnancy and birth were understood, sexual intercourse was important, but sperm and eggs didn’t play a role!
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Really small life?• Microscopes allowed observation of
micro-organisms, but these were thought to come from plants or mud mixed with water (van Leeuwenhoek, mid 1600’s).
• Bacteria in meat broth were formed from the meat (Needham, 1745).
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An alternative view: Biogenesis
• By the mid 17th century some individuals questioned abiogenesis.
• Their observations suggested all living things were produced by other living things– Biogenesis
• A test of biogenesis/abiogenesis was needed!
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Francisco Redi• 1668: An Italian physician decided to
test the “common knowledge” that maggots came from rotting meat.– Without refrigeration or concern about
covering food, maggots tended to appear on meat within a few days. Therefore, the meat produced the maggots.
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• OBSERVATION: Flies land on meat that is left uncovered. Later, maggots appear on the meat.
• HYPOTHESIS: Flies produce maggots.
Redi’s Alternative:
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Redi’s Experimental Design• If flies are kept away from meat by a
covering, no maggots should appear.• Compare to meat stored in the usual
way (uncovered) which should develop maggots.
• Keep every other factor the same!
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The variables:• Independent variable:
–covering over jar or not• Controls fly access to meat
• Controlled Variables:–jars, type of meat, location,
temperature, time• Dependent variable:
–maggots?
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Uncovered jars Covered jars
Several days pass
?
Procedure
?
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Results
Uncovered jars Covered jars
Several days pass
Maggots appear No maggots appear
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CONCLUSION:
• Maggots form only when flies come in contact with meat. – Spontaneous generation of
maggots did not occur.
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Spallanzani’s Experiment: 1765
Gravy is boiled. Flask isopen.
Gravy is teeming with microorganisms.
Figure 1-10 Spallanzani’s Experiment
Gravy is boiled. Flask issealed.
Gravy is free of microorganisms.
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Pasteur’s Experiment: 1860
Broth is boiled.
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Pasteur
Broth is boiled. Broth is free ofmicroorganismsfor a year.
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Pasteur
Broth is boiled. Broth is free ofmicroorganismsfor a year.
Curved neckis removed.
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Pasteur
Broth is boiled. Broth is free ofmicroorganismsfor a year.
Curved neckis removed.
Broth is teeming with microorganisms.
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Biogenesis wins!• Pasteur’s experiments finally won
general support for the biological origins of living things.
• Pasteur also introduced methods of food preservation (Pasteurization!) that dramatically increased the shelf life of foods.
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But wait! There’s more!
• Where did the FIRST living thing come from???
• Where did the universe come from???
• Let’s start with nonliving things and how they affect living things.
• Abiotic vs Biotic factors!