AnnouncementsAugust 25, 2006

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BBCTuesday, 22 August 2006

Climate linked to plague increase

Up to 3,000 cases of plague are reported each year. Climatic changes could lead to more outbreaks of bubonic plague among human populations, a study suggests.

Researchers found that the bacterium that caused the deadly disease became more widespread following warmer springs and wetter summers.

Aug 21, 2006Trap-jaw ant has world's fastest bite The mandibles of the trap-jaw ant close at speeds up to 145 mph, the fastest predatory strike in the animal kingdom.

Scientists have discovered the fastest bite in the world, one so explosive it can be used to send the ant that performs it flying through the air to escape predators. These powerful jaws could serve as inspirations for the propulsion systems of miniature robots, says researcher Andrew Suarez, an ecologist and entomologist at the University of Illinois at Urbana-Champaign. https://webfiles.berkeley.edu/xythoswfs/webui/_xy-462276_1-t_QmzyUzyF

Basic Scientific Principles

Lecture Objectives:

2. Discuss how to form and test hypotheses.

1. Outline the scientific method.

3. Learn the differences between a scientific theory, law and hypothesis.

4. Understand the limitations of science.

Scientific Thinking

Science — A process used to solve problems or develop an understanding of nature that involves testing possible answers.

Scientific Method — Gaining information about the world by forming possible solutions to questions, followed by rigorous testing to determine if the proposed solutions are valid.

Scientific Method Presumptions

Specific causes for observed events.

Causes can be identified.

General rules can describe observations.Repeated events have same cause.

Perceptions are not individualistic.

Fundamental rules of nature are universal.

Leads to world domination (only for evil scientists).

Scientific Method

Scientific Method

Question — Usually a “how” or “why” question about the cause of the event.

Observation — recording of an event that could be made by anyone with the proper equipment.

Scientific Method

be testable and falsifiable

Hypothesis — Logical statement that potentially explains an event, or answers a question.

A good hypothesis will:

take into account all known facts

be as simple as possible

Test Hypothesis

1. Devise an experiment.

2. Predict the outcome of the experiment if the hypothesis is correct.

Types of experiments:

- Thought experiment

- Observational experiment

- Manipulative experiment

Scientific Method

Manipulative experiment — experimental factors are varied to test hypothesis.

Control – Separate variables and divide experiment into experimental and control groups. There should be only one difference between the experimental and control groups.

Important features of manipulative experiments:

Replication — Experiment is repeated to eliminate unconscious bias or a spurious correlation.

Scientific Method

Conclusion — statement if the hypothesis has been supported or not by the results of the test.

Scientific Method

Hypotheses are never “proven” true!!

If results match predictions, then hypothesis supported.

If results to not match predictions, then hypothesis not supported.

Statistics

A branch of applied mathematics concerned with the collection and interpretation of quantitative data.

Probability

How likely are your results true?

Our ability to accept or reject a hypothesis will be based on the accuracy and precision of our measurements.

Accuracy - an estimate of nearness to the truth or the true value

Precision - the repeatability of reproducibility of a measurement

Observation: The light in your room does not come on when you flip the switch

Question: Why didn’t the light come on?

Question: Why didn’t the light come on?

Hypotheses:

1. The light bulb burned out.

2. The lamp is not plugged in.

3. The electrical outlet is not working.

4. The circuit breaker was tripped.

5. The lamp is broken.

Tests & Predications:

1. If I replace the bulb, the light will come on.

2. If I make sure the lamp is plugged in, ...

3. If I plug the lamp into another outlet, …

4. If I replace the fuse/flip the circuit breaker…

5. ??? No single test - If I do all of the above, the light still will not work.

Light bulb?

Plug? Outlet? Circuit breaker?

Lamp?

Change bulb

Y N N N N

Check plug

N Y N N N

Plug in other

N N Y N N

Check breaker

N N N Y N

If ____ hypothesis is correct, and I do ____ test, will the light come on?

Important to do only one thing at a time!!

Results:

1. The light does not come on after replacing the bulb.

2. The lamp was plugged in.

3. The lamp does not come on when plugged into another outlet.

4. The light does not come on after flipping the circuit breaker.

Conclusions:

The lamp is probably broken.

Why say probably?

Scientific Method

Observation — Amphibian deformities are increasing world-wide

Deformities in Pennsylvania

wood frogs

http://www.science.psu.edu/alert/Kiesecker7-2002.htm#photos

Deformed American toads

Rana sylvatica

Kiesecker, J. M. 2002. Proceedings of the National Academy of Sciences 99:9900-9904

Hypothesis 1: The deformities are caused by a naturally occurring parasite (a disease)

Prior research suggests three main hypotheses:

Hypothesis 2: The deformities are caused by a chemical contaminant in the environment

Hypothesis 3: Chemicals and parasites in combination increase the chance that a deformity will result

Types of Experiments:

Laboratory Field

Pro: Highly controlled

Con: Limited reality

Pro: Highly realistic

Con: Many uncontrolled factors

Trematode cercariae, the infective stage that would attack frogs

Do parasites cause limb deformities in frogs?

Hypothesis 1: The deformities are caused by the parasite

Experiment 1:

Field experiment

6 natural ponds

6 cages per pond

6 cages per pond

In each pond:3 cages allowed the parasite in (exposed)3 cages kept the parasite out (protected/unexposed)

REPLICATION!!!

Percentage of deformities in adult frogs:

Conclusion: Exposure to parasites leads to deformities (Hypothesis 1 supported)

Pond Exposed Protected1 23% 0%2 34% 0%3 27% 0%4 3% 0%5 7% 0%6 4% 0%

Prediction: If parasites cause deformities, then tadpoles exposed to parasites will be deformed, but those protected will not.

But, what about chemicals?

Hypothesis 2: The deformities are caused by chemicals

Same field experiment as before:

Ponds 1-3

Ponds 4-6

High agricultural runoffAtrazineMalathion

Low agricultural runoff

No Atrazine or Malathion detected

Prediction: If deformities caused by chemical exposure, then tadpoles in ponds 1-3 will have deformaties, regardless of parasite exposure.

Percentage of deformities in adult frogs:Pond Exposed Protected1 23% 0%2 34% 0%3 27% 0%4 3% 0%5 7% 0%6 4% 0%

Conclusion: Chemical exposure alone does not seem to cause deformities. (Hypothesis 2 not supported)

Chemicals

No Chemicals

Hypothesis 3: Chemicals and parasites in combination increase the chance that a deformity will result.

Prediction: Tadpoles exposed to parasites in ponds 1-3 (chemicals) will develop more deformities than tadpoles exposed to parasites in ponds 4-6 (no chemicals).

Percentage of deformities in adult frogs:Pond Exposed Protected1 23% 0%2 34% 0%3 27% 0%4 3% 0%5 7% 0%6 4% 0%

Conclusion: The combination of parasites and chemicals increases the development of deformities (Hypothesis 3 supported)

Chemicals

No Chemicals

WHY?

Why do pesticide chemicals increase occurrence of developmental deformities when tadpoles exposed to parasites?

Hypothesis: chemicals weaken the immune system and the tadpole’s ability to fight off infection.

Laboratory experiment:

Atrazine(weed control on crops)

Malathion(mosquitoes and insect control on crops)

Esfenvalerate(insect control on crops)

Control(no chemicals)

Exp

ose

to p

aras

ites

Mea

sure

Infe

ctio

n an

d im

mun

e sy

stem

res

pons

e

Prediction: if chemicals weaken immune system, tadpoles exposed to chemicals will have higher infection levels and a lower immune response than tadpoles not exposed to chemicals.

Results: for all 3 chemical treatments, tadpoles had higher levels of infection and lower numbers of leukocytes in blood.

Conclusions: Agricultural chemicals weaken the immune system of frogs, making them more susceptible to infection by parasites, which cause limb deformities.

Conclusions from the study:

1. Exposure to parasite infection was required for the development of limb deformities in these frogs

2. Deformities were more common in ponds with chemicals than in those without

3. Exposure to the chemicals weakens the tadpole immune system and increases the rate of infection

Scientific Method

Development of Theories and Laws

Theory — A widely accepted, plausible generalization about fundamental scientific concepts that explain why things happen.

Law — A uniform or constant fact of nature that describes what happens in nature.

Hypothesis — Logical statement that potentially explains an event, or answers a question.

Limitations of Science

- Restricted to those things that can be logically tested and falsified.

- More than one hypothesis can predict the same outcome of a test.

- Results can be interpreted in different ways, leading to different conclusions.

- Hypotheses constantly being reevaluated and modified as more results and information are gained.

Points to know:

1. What is “science” and what presumptions does it have?

2. Know the steps in the Scientific method.

3. What are features of a good hypothesis and a controlled manipulative experiment?

4. Why are hypotheses never proven true? What terminology is used?

5. Be able to make a conclusion based on comparing experimental and control groups.

6. Distinguish between a scientific theory, law and hypothesis.

7. What are the limitations of science?