Scientific Method and Experimental Design

What is Science?

What is Science? What is biology? Science – an organized way of using evidence to learn about the natural world Biology – the study of the living world Skills Used By Scientists: Observations skills – scientists use their senses (sight, hearing, touch, smell) to observe nature Hypothesizing skills – scientists attempt to explain observations by forming hypotheses or ideas Analyzing and Interpreting skills – scientists use prior knowledge and experience to analyze and interpret data collected during experiments

How Scientists Work

How Scientists Work Using the Scientific Method State the Problem/Ask a Question Form a Hypothesis & Make a Prediction Test Hypothesis with Experiment Record and Analyze Results Draw a Conclusion Based on Analysis Publish and Repeat Investigations

Writing Hypotheses & Predictions Hypothesis – a possible explanation for a set of observations or possible answer to a scientific question Prediction – a statement, based on the hypothesis that suggests the basic idea for an experiment Usually an if…, then… statement

Writing A Hypothesis Practice Write a possible hypothesis and prediction for each of the following observations. The plants in Mr. Smith’s living room are large, healthy and green but the plants in Mr. Smith’s dining room are small and yellowish in color. All of the fish in the classroom fish tank are healthy except for the algae eaters that keep dying. There are only a few un-popped kernels in the popcorn that has been stored in the kitchen but a lot of kernels left in the popcorn that has been stored in the basement. Can be used as homework or class activity depending on timing. Discuss students’ proposed hypotheses.

Designing Controlled Experiments * Whenever possible, an experiment should be designed to have only ONE variable that is changed at a time. (AKA: Controlled Experiment) Controlled Variable/s – the variable/s that are purposely kept the same Manipulated Variable – the ONE variable that is deliberately changed (also called independent) Responding Variable – the variable that is observed and that changes in response to the manipulated variable (also called dependent) Experimental Group – the group in which the manipulated variable is changed Control or Control Group – the group used as a standard for comparison for the experimental group

Controlled Experiment Practice Hypothesis: Tomato plants given fertilizer will produce more tomatoes than plants that are not fertilized. Plant A Plant B * Both plants are given the same soil, amount of water and sun, temperature, pot size, and growth time. * Plant B is fertilized once a week. What are the controlled variables, the manipulated variable, and the responding variable? Which is the control and the experimental group?

Answers Controlled Variables – soil, amount of water and sun, temperature, pot size, and growth time Manipulated Variable – fertilizer Responding Variable – # of tomatoes Control – Plant A Experimental Group – Plant B

Why change only one variable? Plant A 5 hours of sunlight per day l L of water every 4 days quart sized pot 30°C for 6 weeks no fertilization Plant B 7 hours of sunlight per day l L of water every 2 days gallon sized pot 35°C for 9 weeks fertilized once a week Can’t tell! Why did plant B grow more tomatoes? By only changing one variable, the experimenter can conclude that changes in the responding variable are due only to changes in the one manipulated variable.

Collecting & Representing Data Data - observations and measurements that are made in an experiment All experimental data must include units. (examples: 9cm, 20sec, 98°C) Data is often represented using tables and graphs which must be thoroughly labeled.

Data Collected from an Experiment Storage Location Temperature Inside Room Temp Inside Freezing Temp Outside Winter Temp Percent of germinated seeds 0% 80% 85%

Representing Data in Graphs Storage Temperature Effects on Seed Germination 100 80 60 40 20 Percent of Germinated Seeds (%) - Inside Room - Inside Freezing - Outside Winter Storage Location Temp

Collecting & Representing Data Practice Using the data below, re-draw the data table and graph to improve them. Results: Frogs given caffeine jumped 27cm and frogs not given caffeine jumped 20 cm. Frog not given caffeine Frog given caffeine Distance of jump 20 27

Frog not given caffeine Graph needs a label on the X and Y axis and a key. Table needs units. Effect of Caffeine on Frog Jumps Frog not given caffeine Frog given caffeine Distance of jump 20cm 27cm Distance of jump (cm) Frogs

Drawing Conclusions Conclusion – a final statement that sums up the results of the experiment Conclusion is based on whether the data supports or refutes the hypothesis.