Chapter 1-2: How Scientists Work

Section 1-2: How Scientists Work Designing an

Experiment Steps:

• Asking questions, making observations.

• Forming Hypothesis (must be testable)

Section 1-2: How Scientists Work• Setting up a controlled experiment – isolate and test one variable

Manipulated variable – (Independent variable) the variable that is deliberately changed

Responding variable – (Dependent variable) is variable that is observed

• Record and analyze results

• Draw a conclusion

• Repeat!

Scientists publish their experiments and results. Then other scientists will do the experiments again to test the results.

Repeating Investigations Aristotle – (Father of Biology) made

extensive observations on the natural world; 2300 years ago

At this time people believed in spontaneous generation• Life could arise from nonliving matter• E.g. Recipes for Bees

Some weird recipes….

Recipe for bees:

1) Kill a young bull 2) Bury it in an upright position so that its horns

protrude from the ground. 3) After a month, a swarm of bees will fly out of the

corpse.

Jan Baptista van Helmont’s 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.

Redi’s Experiment (1668)

• Observation: Flies land on meat that is left uncovered. Later, maggots appear on the meat.

• Hypothesis: Flies produce maggots.

Redi’s Experiment (1668)• Procedure Controlled Variables: jars, types of meat, location, temperature, time

Manipulated Variable: gauze covering that keeps flies away from meat

Responding Variable: whether maggots appear

Redi’s Experiment (1668) cont’d..• Data: Shows that maggots appeared on meat with not covered with gauze; those covered with gauze had no maggots

• Conclusion: Maggots form only when flies come in contact with meat. Spontaneous generation of maggots did not occur!

…….well duh….

When Experiments Are Not Possible To learn how animals

act in the wild and interact with others in their group, researchers carry out field studies.

• It is necessary to observe the animals without disturbing them to collect meaningful data.

Scientists will try to identify as many variables as possible so that experiments are as controlled as possible.

How a Theory Develops Once a hypothesis is supported by

repeated experimental data the hypothesis may become a theory.

In science, the word theory applies to a well tested explanation that unifies a broad range of observations.

How a Theory Develops

Theories may be revised or replaced by a more useful explanation.

Sometimes more than one theory is needed to explain a particular circumstance.

• E.g. Why are Marsupial mammals found only in Australia and surroundingislands? Evolution and plate tectonics