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