Life!

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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 - Organization
• 2. Reproduction
• 3. Based on DNA
• 4. Growth and Development
• 5. Need for Energy
• 6. Response to Environmental Stimuli
• 7. Homeostasis
• 8. 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 dont fit with
  the old?
• How did observations lead to hypotheses on life?

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Where does life come from?

• At least by Aristotles 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
  didnt 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 1600s).
• 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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Redis Alternative

• OBSERVATION Flies land on meat that is left
  uncovered. Later, maggots appear on the meat.
• HYPOTHESIS Flies produce maggots.

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Redis 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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Procedure
Uncovered jars
Covered jars
Several days pass
?
?
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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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Spallanzanis Experiment 1765
Figure 1-10 Spallanzanis Experiment
Gravy is boiled.
Flask is open.
Gravy is teeming with microorganisms.
Flask is sealed.
Gravy is free of microorganisms.
Gravy is boiled.
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Pasteurs Experiment 1860
Broth is boiled.
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Pasteur
Broth is boiled.
Broth is free of microorganisms for a year.
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Pasteur
Broth is boiled.
Broth is free of microorganisms for a year.
Curved neck is removed.
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Pasteur
Broth is boiled.
Broth is free of microorganisms for a year.
Curved neck is removed.
Broth is teeming with microorganisms.
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Biogenesis wins!

• Pasteurs 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! Theres more!

• Where did the FIRST living thing come from???
• Where did the universe come from???
• Lets start with nonliving things and how they
  affect living things.
• Abiotic vs Biotic factors!