1. And how we try to figure it out
Life!
And how we try to figure it out

2. Figure 1.2 The hierarchy of biological organization
At each level of increasing complexity, new properties emerge. At what level do we have “life”?

3. Biology Define life (good luck!).
How do we know a living thing when we see one?
list characteristics common to ALL living things.

4. 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

5. What makes Biology a science?
How do you know science when you see it?
list some characteristics of science and describe how scientists work.

6. Science is… Objective Data driven Experimental
Attempt to find the best possible naturally occurring explanation for a phenomenon.

7. 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?

8. 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.

9. 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!

10. 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).

11. 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!

12. 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.

13. Redi’s Alternative:
OBSERVATION: Flies land on meat that is left uncovered. Later, maggots appear on the meat.
HYPOTHESIS: Flies produce maggots.

14. 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!

15. 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?

16. Procedure
Uncovered jars
Covered jars
Several
days pass ? ?

17. Results Uncovered jars Covered jars Several days pass Maggots appear
No maggots appear

18. CONCLUSION: Maggots form only when flies come in contact with meat.
Spontaneous generation of maggots did not occur.

19. Spallanzani’s Experiment: 1765
Figure 1-10 Spallanzani’s Experiment
Spallanzani’s Experiment: 1765
Gravy is boiled.
Flask is
open.
Gravy is teeming
with microorganisms.
Flask is
sealed.
Gravy is free of
microorganisms.
Gravy is boiled.

20. Pasteur’s Experiment: 1860
Broth is boiled.

21. Pasteur
Broth is boiled.
Broth is free of
microorganisms
for a year.

22. Pasteur Broth is boiled. Broth is free of microorganisms for a year.
Curved neck
is removed.

23. Pasteur Broth is boiled. Broth is free of microorganisms for a year.
Curved neck
is removed.
Broth is
teeming with microorganisms.

24. 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.

25. 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!