Scientific Method Review Scientific method is fair game on all weekly quizzes and exams.

A do it yourself cheat sheet The notes you take from this powerpoint may (and should) be used on some upcoming assignments. If you don’t understand something, ask, because you will be graded

Controlled experiments There is something we want to explain. More specifically, why does the value of a variable change?

Controlled experiments The experiment is called a controlled experiment because only one thing is varied at a time, while everything else we think might affect the outcome is kept constant (controlled). This is so we know that any changes we see in the variable we are interested in is due to the one thing we changed.

Variables A variable is anything that might take on different values in an experiment. Ex: temperatures, lengths, masses, growth rates vary. We place these variables into 3 classes. –Independent –Dependent –Controlled

Independent Variable The variable the experimenter chooses to change. Also called the manipulated variable. It’s called independent because when one is independent you make choices.

Independent variable Independent suggests choice. So the independent variable is the one the experimenter chooses to investigate.

Dependent Variable Also called the responding variable. This is the variable that responds to changes the experimenter makes to the independent variable. It depends on the independent variable This is what you observe happening in the experiment. This is also the data you record in a data sheet or electronic device.

Controlled Variables These are the things that are kept constant in an experiment. Anything that might confuse the interpretation of the experiment. Any other variable that could have an effect on what you observe in the experiment. These are other potential independent variables that you might choose to vary and test in a future experiment.

Variables (example) Does the brand of cat food affect the incidence of furballs? What are the variables? Obvious from question –Incidence of furballs –Brand of cat food Not so obvious –Age or type of cat –Cat’s environment (indoor?) –Amount of cat food –How often they eat –Length of hair independent dependent controlled

Which variables go in which categories? Independent variable –Brand of cat food Dependent variable –Incidence of furballs Controlled variables –All the “not so obvious” variables –Age, hair length, etc.

What is a testable question or problem that is the basis for this investigation? “What is the effect of light intensity on the rate of photosynthesis?” Two students were doing an investigation in which they studied the effect of light intensity on the rate of photosynthesis of Elodea, an aquarium plant. To determine the rate of photosynthesis, they counted the number of bubbles of oxygen produced in the water.

“What is the effect of light intensity on the rate of photosynthesis?” What is the independent variable? light intensity What is the dependent variable? rate of photosynthesis Two students were doing an investigation in which they studied the effect of light intensity on the rate of photosynthesis of Elodea, an aquarium plant. To determine the rate of photosynthesis, they counted the number of bubbles of oxygen produced in the water.

Rule for answering “what is the question or problem?” “What is the effect of independent variable on dependent variable?” “What is the effect of ____________ on ____________?”

Write an appropriate hypothesis for this investigation Or… Write an appropriate testable hypothesis Two students were doing an investigation in which they studied the effect of light intensity on the rate of photosynthesis of Elodea, an aquarium plant. To determine the rate of photosynthesis, they counted the number of bubbles of oxygen produced in the water.

Rule for “Write an appropriate hypothesis.” “If (the change in the independent variable) then, (the observed changes in the dependent variable) will (prediction of change)”

Write an appropriate hypothesis for this investigation. If we increase light intensity, then the rate of photosynthesis (or number of bubbles of oxygen) will increase. Two students were doing an investigation in which they studied the effect of light intensity on the rate of photosynthesis of Elodea, an aquarium plant. To determine the rate of photosynthesis, they counted the number of bubbles of oxygen produced in the water.

The difference between laboratory equipment and procedure Laboratory equipment is: Permanent or durable –Ex. beakers, thermometers, containers, timers, etc. Specific to the experiment –Wrong answers include sink, table, data tables, charts, computers, etc. not consumed or living –Wrong answers include chemicals, water, plants, animals, etc.

The difference between laboratory equipment and procedure A procedure is: An action (doing something) –Ex. measuring volume, length, mass –Ex. counting things –Ex. using specific lab equipment –Ex. quality control – making sure equipment and procedures are consistent.

Data Tables Title –Rule: “The effect of the independent variable on dependent variable.” The column headers (title) will identify the variables.

Simple Data Tables Independent var. (unit) Dependent var. (unit) This format is for a simple single-line graph X- axis Y- axis

Complex Data Tables This format is for a multi-line graph Dependent variable (unit) Indepen- dent var. (unit) Control (or control group) Treatment 1 (or experimental group) Treatment 2 (or experimental group) These represent the different lines on your graph and are identified in the legend (or key) X- axis Y-axis All of the data in the table below the main column header have the same units.

Graphing Dependent variable Independent variable Y-axis X-axis

Graphing - multiline When we are dealing with a multiline graph, we need to be careful to choose the correct variable for the x-axis. Even though the experiment’s treatments (different drugs, different species, different fertilizers, etc.) are independent variables, we show them as different lines, not on the x-axis. Instead, we use the most consistent unit of measure (usually time) for the x-axis.

Multiline graph example 1 Channel catfish fry were fed two rates of feeding. Their growth was measured once a week for 3 months. Variables Independent Dependent Rate of feeding Growth Time rate 1 rate 2

Multiline graph example 1 Channel catfish fry were fed two rates of feeding. Their growth was measured once a week for 3 months. Growth (g) Time (wk) Feed rate 1 Feed rate Etc. Time (wk) Growth (g)

Multiline graph example 2 Two drugs were tested for their effectiveness in reducing cholesterol. They were each tested at doses of 0, 5, 10, 15 and 20 mg. Variables Independent Dependent Drugs Cholesterol (units) Dose (mg) Drug b Drug a

Graphing Use distinctive markers for the points (x, o, *, etc.) Use distinctive lines (solid, dotted, dashed, etc.)

Graphing Only include recorded data points Do not: –Extend lines beyond your data –Extend lines to origin (0,0) Exceptions: –Lines of best-fit –When origin (0,0) is actually a data point Ex. data starts at 0 sec. or 0 meters

Dependent Variable Also called the responding variable. This is the variable that responds to changes made by the experimenter to the independent variable. This is what you observe happening in the experiment.