life!
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Life!. And how we try to figure it out. Figure 1.2 The hierarchy of biological organization. Biology. Define life (good luck!). How do we know a living thing when we see one? list characteristics common to ALL living things. Characteristics of all living things:. - PowerPoint PPT PresentationTRANSCRIPT
Life!
And how we try to figure it out
Figure 1.2 The hierarchy of biological organization
Biology
• Define life (good luck!).
• How do we know a living thing when we see one?– list characteristics common to
ALL living things.
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
What makes Biology a science?
• How do you know science when you see it?– list some characteristics of
science and describe how scientists work.
Science is…
• Objective
• Data driven
• Experimental
• Attempt to find the best possible naturally occurring explanation for a phenomenon.
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?
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.
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!
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).
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!
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.
• OBSERVATION: Flies land on meat that is left uncovered. Later, maggots appear on the meat.
• HYPOTHESIS: Flies produce maggots.
Redi’s Alternative:
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!
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?
Uncovered jars Covered jars
Several days pass
?
Procedure
?
Results
Uncovered jars Covered jars
Several days pass
Maggots appear No maggots appear
CONCLUSION:
• Maggots form only when flies come in contact with meat. – Spontaneous generation of
maggots did not occur.
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.
Pasteur’s Experiment: 1860
Broth is boiled.
Pasteur
Broth is boiled. Broth is free ofmicroorganismsfor a year.
Pasteur
Broth is boiled. Broth is free ofmicroorganismsfor a year.
Curved neckis removed.
Pasteur
Broth is boiled. Broth is free ofmicroorganismsfor a year.
Curved neckis removed.
Broth is teeming with microorganisms.
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.
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!