Experimental Design Pre-AP Biology

Bell Work Judy observes her two potted plants. One has grown significantly bigger and fuller than the other. Judy wants to see if it is caused by the amount of sunlight that they receive. She plants two different flowers using the same bag of potting soil. She waters them both at the same time each day. She places one in direct sunlight and the other in indirect sunlight. 1. What did Judy do wrong in her experiment? 2. What did Judy do right in her experiment? 3. What would you do differently?

Science A way of learning about the natural world Includes all of the knowledge gained by exploring the natural world This knowledge is always growing and changing as scientists ask new questions and explore new ideas

Scientific Inquiry Scientific: Of or relating to the practice of science Inquiry: A close examination of a matter in a search for information or truth Scientific Inquiry: The ways in which scientists explore the natural world

How Does Scientific Inquiry Work? Scientific Method: Make observations and/or inferences Ask questions Develop hypotheses Design experiments Make measurements Collect data Interpret data Draw conclusions Communicate

Make Observations and Inferences Observation: Using one or more of your senses to collect data Inference: An interpretation of an observation that is based on evidence or prior knowledge Data: Facts, figures and other evidence gathered through observation

Hypothesis

Hypothesis Proposed explanation based on limited evidence as a starting point for further investigation

Experiment

Experiment A scientific procedure that answers a question or solves a problem

Designing an experiment to test a hypothesis After you state your hypothesis, you must design an experiment to test it. You figure out a way to test whether the hypothesis is supported. Control group– nothing changed Experimental group – one variable changed The outcome must be measurable (quantifiable). Record and analyze data.

Independent Variable: Dependent Variable: Controlled Variables:

Independent Variable: factor that you want to test or manipulate (CAUSE) Dependent Variable: factor you observe or measure during the experiment (EFFECT) Controlled Variables: factors that are the same for all groups; must be kept the same so that effect of independent variable can be seen.

Variables Does the height at which a ball is dropped affect the bounce height of the ball? Independent variable:

Variables Does the height at which a ball is dropped affect the bounce height of the ball? Independent variable: Drop height We know the height of the ball drop; we control this.

Variables Does the height at which a ball is dropped affect the bounce height of the ball? Independent variable: Drop height We know the height of the ball drop; we control this. Dependent variable:

Variables Does the height at which a ball is dropped affect the bounce height of the ball? Independent variable: Drop height We know the height of the ball drop; we control this. Dependent variable: Bounce height The bounce height depends on the drop height. It is what we measure.

Variables Does feeding a dog a high-calorie diet lead to weight gain? Independent variable:

Variables Does feeding a dog a high-calorie diet lead to weight gain? Independent variable: Calories in diet We know what we will feed the dog.

Variables Does feeding a dog a high-calorie diet lead to weight gain? Independent variable: Calories in diet We know what we will feed the dog. Dependent variable:

Variables Does feeding a dog a high-calorie diet lead to weight gain? Independent variable: Calories in diet We know what we will feed the dog. Dependent variable: Dog’s weight We don’t know how the weight will change before we start. It is what we measure.

Variables Does taking a weight loss supplement lead to weight loss? Independent variable:

Variables Does taking a weight loss supplement lead to weight loss? Independent variable: Weight loss supplement We control whether we take the weight loss supplement.

Variables Does taking a weight loss supplement lead to weight loss? Independent variable: Weight loss supplement We control whether we take the weight loss supplement. Dependent variable:

Variables Does taking a weight loss supplement lead to weight loss? Independent variable: Weight loss supplement We control whether we take the weight loss supplement. Dependent variable: Weight We don’t know whether we will lose weight until we take the supplement. It is what we measure.

Variables Do cancer cells stop replicating when exposed to an experimental cancer drug? Independent variable:

Variables Do cancer cells stop replicating when exposed to an experimental cancer drug? Independent variable: Cancer drug We control whether we expose the cells to the cancer drug.

Variables Do cancer cells stop replicating when exposed to an experimental cancer drug? Independent variable: Cancer drug We control whether we expose the cells to the cancer drug. Dependent variable:

Variables Do cancer cells stop replicating when exposed to an experimental cancer drug? Independent variable: Cancer drug We control whether we expose the cells to the cancer drug. Dependent variable: Replication of cancer cells We don’t know until we expose the cells to the treatment whether they will stop replicating. It is what we measure.

Control Group: Experimental Group:

Control Group: group that does NOT receive the independent variable; is not tested on Experimental Group: group that DOES receive the independent variable; is tested on

Designing a Controlled Experiment An experiment in which all of the variables except for one are remain the same An experiment that is designed to compare an experimental group with a control group. Ideally, a control group and an experimental group differ in only one variable. Control group serves as a comparison to measure against

Controlled Experiment A drug manufacturer is testing a new drug to treat gout. An investigator dispenses a placebo (sugar pills containing no drug) to one group. The other group receives pills containing the actual drug. Which group is the control group? Which group is the experimental group?

Constants Constant: a variable that does not change for the duration of an experiment; a value that remains the same Example: Ball being dropped from different heights - Same ball is used every time (remains constant)

Interpreting Data You do the experiment using the method you came up with and record the results. After the data are collected, they must be organized and interpreted Create data tables, graphs to represent data Perform calculations that will determine what results mean (averages, percentages, totals) Identify possible sources of errors

Conclusion

Conclusion Results of the experiment

Drawing Conclusions After you have organized and interpreted your data, you must draw a conclusion. You need to decide if the data support your original hypothesis.

Communicating Scientists must communicate their findings to other scientists. This contributes to the growth of the body of scientific knowledge.

Scientific Theories Scientific Theory: A well-tested concept that explains a wide range of observations. A theory is based on thousands of experiments done by different scientists. A theory is much broader in scope than a hypothesis. Theories only become widely accepted in science if they are supported by an accumulation of extensive and varied evidence. Future testing may prove a theory to be incorrect.

Claims, Evidence and Reasoning (CER)

Claims, Evidence and Reasoning (CER) My dad’s an alien CER Infomercial

Claim Statement that answers your original question Usually one sentence in length Must be accurate, specific, and completely answer the question Clear: Does not use vague words such as “they”, “it”, or “stuff” Concise: To the point, with no unnecessary words (“I think”, “Based on my lab”)

Claim Examples?

Claim Examples? Smoking cigarettes leads to lung cancer. Eating dark chocolate promotes heart health. Consuming caffeine leads to high blood pressure.

Evidence Scientific data that supports your claim Evidence must be sufficient and relevant to your claim. Not all data is considered evidence! May be data generated from a lab, or may come from trusted sources (textbook, notes, websites, etc.) The more evidence you have, the better able you are to prove your claim. Example: According to epidemiological studies, lung cancer prevalence is higher in smokers than in nonsmokers. In vitro (laboratory) studies have demonstrated that exposing cells to substances in cigarettes leads cells to mutate.

Evidence Examples?

Evidence Examples? According to epidemiological studies, lung cancer prevalence is higher in smokers than in nonsmokers. In vitro (laboratory) studies have demonstrated that exposure of cells to substances in cigarettes leads to mutations.

Reasoning Explanation that connects your claim to the evidence that supports it Shows why the data you chose counts as evidence by using appropriate and sufficient scientific principles Acts as the “conclusion” of your experiment Shows a detailed understanding of the scientific principles involved and uses correct science vocabulary At least a few sentences in length

Lab Report Guidelines I. Title II. Introduction III. Materials and Procedures IV. Results/Data Collection/Analysis V. Discussion/Conclusion VI. Literature Citation VII. Questions

Lab Report Guidelines: Title Primary topic dealt with during the experimentation. Clear and concise; avoid extra words

Lab Report Guidelines: Introduction a. Background information that will help them understand the experiment that you have conducted. Important terms should be defined in the section. b. Purpose of the lab and should be clearly stated in the introduction. c. Hypothesis – a testable hypothesis should be included, written in an if-then format.

Lab Report Guidelines: Materials & Procedures A complete listing of the materials and supplies that were used to conduct the experiment should be included in this portion of the report. In this section of the report you should present the exact steps that were followed in your experiment. Clearly identify the control, variables and the measurement techniques used.

Lab Report Guidelines: Results/Data Collection/Analysis All of the data that was collected during the experiment should be presented in a data table or tables. Additionally, a graph of the data should be included in this section. Make sure that the graph is appropriately titled and axes labeled. Include a legend if necessary.

Lab Report Guidelines: Discussion/Conclusions This portion of the report is used to clearly explain whether the results support or refute the hypothesis being tested. Explain what your findings mean and what conclusions you can draw from the data. Sources of error and suggestions for improvement should be included in this section.

Lab Report Guidelines: Literature Citation If any of the information included in your lab write up was taken from a published lab activity, you should include a citation of the source. The source(s) used should be cited within your lab write-up (especially in the introduction section) using scientific citation. Example: (College Board, 2001).

Lab Report Guidelines: Question The discussion questions found throughout the laboratory should be written and answered in this section.