BIO 10 Lecture 1

1. BIO 10 Lecture 1 HOW SCIENTISTS VIEW THE WORLD

2. Which of the following statements best describes SCIENCE? • Science is a collection offacts about the Universe and how it behaves • Science is a collection oftheories that have predictive power • Science is a methodof learning about the Universe and its behavior

3. SCIENCE is ALL these things! Scientific factsare irrefutable statements about nature such as “The Earth is spherical, not flat.” Although it certainly appears to the casual human observer that the Earth is flat, we now KNOW, as a fact, that this is not true.

4. How do we Know? At one time, the idea that the Earth was a sphere was merely a THEORY based on certain observations. For example: Sailors observed that the tops of mountains and buildings come into view above the horizon before objects nearer to the ground

5. Aristotle argued for a spherical Earth because the border of the shadow of Earth on the Moon during the partial phase of a lunar eclipse is circular.

6. BUT …How do we really KNOW for sure?Why do scientists now consider a spherical Earth to be FACT and not merely aTHEORY??

8. Scientific theoriesare sets of general principles, supported by facts, that have predictive power. “The Universe started with a Big Bang.” Although the theory of the Big Bang has a great deal of explanatory power, it cannot be directly observed, and it still cannot explain some of the key observations in physics …

9. The Big Bang theory explains the observed background “temperature” of space, the current size of the Universe, and the observation that the Universe is expanding • However, scientists cannot be sure that the Big Bang is the best theory for how the Universe began. • Perhaps another theory – as yet undeveloped – will have even more explanatory power and will not be assailable by experimentation over time

10. What IS certain, however, is that scientists won’t abandon a good theory unless a better one comes along • The new theory must be more predictive and explain more observations than the former theory • Thus, scientific theories can – and foten do - change over time, but, when they do, they do so in a directedmanner • Over time, theories thus become better and better at modeling how the Universe is actually put together and can even eventually become widely accepted as fact

11. Fact or Theory? • There are 50 U.S. States • All crows are black • The DNA sequence of humans and chimps is 98% identical • There is life elsewhere in the Universe • Humans and chimps evolved from a common ancestor

12. The Scientific Methodis a way of learning about the Universe that uncovers scientific facts and helps scientists build better theories. • Unlike other ways of learning about the Universe, science (when it is done well): • Begins with observations about the World and its behavior • Develops testable hypotheses that might explain the observations • Systematically eliminates hypotheses through careful experimentation • Takes no prisoners

14. Observation: • When I eat asparagus, my urine smells funny afterwards. My husband says his urine does not smell after he eats asparagus. • Can we develop one or more testable hypotheses to explain this observation?

15. First Testable Hypothesis My husband produces the smelly substance in his urine after he eats asparagus but lacks the ability to smell it.

16. Design an Experiment: • In Class Exercise

17. Spontaneous Generation • Let’s look at a historical example of good scientific method and experimental design. • Aristotle (384-322 B.C.) proposed the theory of spontaneous generation • Also called abiogenesis • Idea that living things can arise from nonliving matter • Idea lasted almost 2000 years

18. In Aristotle’s time, people based their beliefs on their interpretations of what they saw going on in the world around them without systematically testing their ideas • They didn’t use the scientific method to arrive at answers to their questions • Their conclusions were therefore based on untested observations

19. Observation: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. • However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times. • Untested Conclusion: Muddy soil must give rise to the frogs.

20. Observation: In many parts of Europe, medieval farmers stored grain in barns with thatched roofs (like Shakespeare’s house). • As a roof aged, it was not uncommon for it to start leaking. • This could lead to spoiled or moldy grain, and of course there were lots of mice around. • Untested Conclusion: • Mice must come from the moldy grain…

21. Observation: In European cities centuries ago, there were no sewers, no garbage trucks, no electricity, and no refrigeration. • Sewage flowed down the streets, and chamber pots and left over food were thrown out into the streets each morning. Many cities also had major rat problems and a disease called Bubonic plague. • Untested Conclusion: The sewage and garbage turned into the rats.

22. Ambiogenesis Recipes • Recipe for bees: • Kill a young bull, and bury it in an upright position so that its horns protrude from the ground. After a month, a swarm of bees will fly out of the corpse. • Recipe for mice: • Place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat or some wheat bran, and in 21 days, mice will appear. There will be adult males and females present, and they will be capable of mating and reproducing more mice.

23. Disproving Spontaneous Generation through Science • Redi’s (1626-1697) Experiments: Evidence against spontaneous generation: 1. Unsealed – maggots on meat 2. Sealed – no maggots on meat 3. Gauze – few maggots on gauze, none on meat

24. The results of Redi’s experiment disproved the idea of spontaneous generation for larger organisms, but people still thought microscopic organisms like algae or bacteria could arise that way … • LazzaroSpallanzani’s Experiments (1765)

25. Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “life force” • Therefore, spontaneous generation remainedthe theory of the time • By 1860, the debate had become so heated that the Paris Academy of Sciences offered a prize for any experiments that would help resolve this conflict • The prize was claimed in 1864 by Louis Pasteur, as he published the results of an experiment that disproved the hypothesis that spontaneous generation occurs in microscopic organisms

27. Hypothesis:Microbes come from cells of organisms on dust particles in the air; not the air itself. • Experiment: • Pasteur put broth into several special S-shaped flasks • The special shape was intended to trap any dust particles containing bacteria • The broth in each flask was boiled and allowed to cool • The tips of some flasks were left intact while the tips of others were broken

29. Pasteur’s S-shaped flask kept microbes out but let air in, proving that the lack of bacterial growth was NOT the result of a lack of sufficient air • Supported the view that microbes only come from other microbes (life from life) - biogenesis • Since that time, all experiments that have attempted to disprove biogenesis have failed, which is why biogenesis is now considered to be a FACT

30. Lecture 1 Review 1. How is science different from other methods of gathering information? (E.g. casual observations, book-learning, listening to parents, teachers, or friends, reading the Bible) 2. State a hypotheses that cannot be subjected to scientific analysis. 3. Does science ever prove anything? Give one example. • Does science ever disprove anything? Give one example. • In what important way did Pasteur’s experimental design improve on Spallanzani’s? • Can you smell a strange odor in your own urine after you eat asparagus?