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

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

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.

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

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?

Procedure Uncovered jars Covered jars Several days pass ? ?

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 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.

Pasteur’s Experiment: 1860 Broth is boiled.

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

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

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