EXPERIMENTAL DESIGN AND THE SCIENTIFIC METHOD

Graphs We will use various graphs when we analyze and conduct experiments in class You will also use graphs as a visual way to show data When you take Biology, you will be expected to know what each part of a graph means and how to answer specific questions using data from a graph

3 Main Types of Graphs Bar Graph Line Graph Pie Graph (often called a pie chart)

Bar Graph Use a bar graph when comparing Qualitative Data (categories) and numbers For Example: Number of each color car in the parking lot

Pie Graph Use pie graphs when looking at percentages of a whole For Example: What percentages of each element make up the earth’s crust?

Line Graph  Use line graphs when comparing two types of Quantative data (two sets of numbers)   For Example: Amounts of water (mL) effects on plant height (cm)

( what you are measuring) (what I change in the experiment) Parts of a Graph Dependent variable (on Y-axis) Independent variable (on X-axis) Title (IV versus DV) Numbers of measurement in eve n increments ( what you are measuring) Dependent Variable Independent Variable (what I change in the experiment)

Draw This Diagram!

1—OBSERVE!!! Make observations about the world around you—this is what scientists do and this leads to a question Example: My grass isn’t growing.

2—QUESTION??? Form a question about something you want to know about. (typically based on the observation) Example: Why isn’t my grass growing?

3—HYPOTHESIS This is an educated guess as to the answer to the question “If…,then…” MUST be testable Does NOT start with “I think…” Example: If part of the grass is watered and part is left unwatered, then the watered part will grow more.

4—TEST YOUR HYPOTHESIS Do an experiment—write a procedure so that someone else can repeat it Variables--anything that can be changed in an experiment Independent variable—the variable the experimenter is changing/manipulating Dependent Variable—the variable that is being measured (it changes as a result of what the experimenter changed)

Control Group—the standard for comparison in an experiment, the group that remains the same and does not receive the IV Replicates—test the experiment many times so that results aren’t random (also know as trials) Constants—everything in an experiment that is kept the same to ensure the IV is what caused the outcome of the experiment (change only the IV, nothing else)

Example: Testing the hypothesis would be splitting lawn into 8 chunks, not watering 4 of them, and watering the other 4 with a consistent amount of water. What would the independent variable be? Amount of water What would the dependent variable be? Growth of grass/lawn What would the control group be? The part of the lawn with no water.

Example Continued… How many trials are there? 4 What are some things that need to be held constant in an experiment? Amt. of sunlight, amt. of fertilizer, location of grass, person watering, type of grass

5—COLLECT & GATHER DATA Observe what happened and write it down on a data table. Average height of grass—No Water Average height of grass--Watered 500 mL/day Before starting 5 cm After Week 1 6 cm 9 cm After Week 2 15 cm After Week 3 7 cm 23 cm After Week 4 7.5 cm 28 cm

5 (2nd part) GRAPH YOUR DATA Create a line or bar graph to show your data Use a line graph if both sets of data are numeric Use a bar graph if one set is words/categories X-axis contains Independent Variable Y-axis contains Dependent Variable Title must be IV vs. DV Both axes must be labeled w/correct units Use increasing even increments along axes

6—RESULTS Summarize what data table says in sentence form—factual information only!!! NO opinions!!! Example: Both sets of grass began at a height of 5 cm. Not watering the grass caused an overall average growth of 2.5 cm after 4 weeks, whereas watering the grass caused an overall average growth of 28 cm after 4 weeks.

7—DRAW A CONCLUSION After looking at results, tell what the outcome of the experiment is Support or reject the hypothesis If hypothesis is rejected, make a new one. Example: Watering the grass does cause the grass to grow more than not watering it. The hypothesis is supported by the data (accept).

TIPS/GUIDELINES Throughout the writing of an experiment, never use personal pronouns (I, me, we, us, etc.) When graphing, you CANNOT include any breaks!!! No naked numbers on graphs, data tables, results, conclusions, etc. Be as specific as possible with everything!!! The experiment must be repeatable w/o asking questions.

I want to see if vinegar or water boils the fastest I want to see if vinegar or water boils the fastest. What is the independent variable? boiling Speed of boiling Type of liquid Person testing

I want to see if vinegar or water boils the fastest I want to see if vinegar or water boils the fastest. What is the dependent variable? boiling Speed of boiling Type of liquid Person testing

I want to see if girls or boys are better in Science I want to see if girls or boys are better in Science. What is the independent variable? Gender of the student Grade earned in class Person testing Science Class

I want to see if girls or boys are better in Science I want to see if girls or boys are better in Science. What is the dependent variable? Gender of the student Grade earned in class Person testing Science Class

The independent variable is graphed along the x-axis. True False

What is the scientific method? A statement of fact. A way to graph information. A rigid step-by-step process. A way to answer a question or solve a problem.

Why do we repeat an experiment several times? To ensure our results aren’t random. It’s so much fun! That’s just the way things are. To make the experiment testable.

Which of the following would be a CORRECT hypothesis? I think Super Fertilizer will make the plants grow the tallest. Super Fertilizer will make the plants grow the tallest. If Super Fertilizer is added to the plants, then they will grow the tallest. Super Fertilizer is so super, it will help plants grow tall.

Based on the Graph, what is the independent variable? Plant Growth Amount of Water cm mL

Based on the Graph, what is the dependent variable? Plant Growth Amount of Water cm mL

If comparing Super Fertilizer to Fertilizer X and no Fertilizer, what is the control group? The amount of Fertilizer