Scientific Method

Chapter 1

What is Science?

• “The goal of science is to investigate and understand the natural world, to explain events in the natural world, and to use those explanations to make useful predictions.”

• (Biology Text Book)

How do we do this?• Scientific Method

• Series of logical steps used to find answers or new questions

• PHEOCR (Prancing Horses Elated On Candy Rocks)• Refer to handout

• Problem – The question you’re trying to answer• Hypothesis – must be a testable idea

• MUST be in the form of a statement• Experiment (or collect/analyze data)• Observations – 2 types of data to collect

• Quantitative – number/measurement data• Qualitative – non number observations

• Conclusion – Support or refute your hypothesis…you can NEVER prove your hypothesis correct!!!!!!!!!!!!!!!!!

• Repeat

Variables• Variables come in three main types:

• Manipulated (Independent)• Responding (Dependent)• Constant

• Manipulated variable (Only 1 per experiment)• The scientist has direct control of this variable• This variable is the only variable that is changed between

experiment groups• Responding variable

• The scientist has NO direct control of this variable• This variable changes in response to the experiment• Normally the responding variable is a result of the experiment

and depends on what the manipulated variable is• Constant variables

• These variables stay the same through the entire experiment, no matter what

• There are many constant variables in every experiment

Variable Example• You hear drinking only carrot juice for a

long period of time will turn you orange. To test this, you have 5 people drink nothing but carrot juice for 1 week, and 5 people drink nothing but water for 1 week. • Of the 5 drinking carrot juice, 5 turned orange• Of the 5 drinking water, 5 stayed normal

• Identify the Manipulated, Responding and 2 constant variables

Mythbusters: Bull in China Shop

• Mythbusters are the Masters of experimental design!

• Create a hypothesis: What do you think will happen if bulls are let loose in a china shop?

• Watch the “Bull in China Shop” clip YouTube - Mythbusters: Bull In A China Shop and make notes of the• Manipulated Variable• Responding Variable• Constant Variables

Graphs• There are two main types

of graphs used in this class:• Bar Graphs• Line Graphs

• Bar graphs are used for comparisons between variables (usually groups or categories)

• Line graphs are used for change over time

• X-Axis = Manipulated (Independent) Variable

• Y-Axis = Responding (Dependent) Variable

Rules of Graphing• ALWAYS use PENCIL• (0,0) is always the origin• Please DON’T use Graph breaks• The numbers should go up by the same increment at

every line• EX: by 2’s, 5’s, 10’s, 100’s etc

• The x-axis scale and y-axis scale CAN be different• If you don’t have a point for (0,0) in the data table,

don’t start your line at (0,0)• Bars must be the same width in a bar graph• Make sure to label the title, x and y axis and include

UNITS

Which Graph to Use?• Let’s go back to the Bulls in the China

Shop• What type of graph would you use to show how

many dishes were broken in relationship to the number of bulls in the pen?

• Which variable (# of bulls or # of broken dishes) goes on the X-Axis?

• In your notebook, create a bar graph comparing the number of bulls in the pen to the number of dishes that fell.

The Metric System

• Scientists use a common system of measurement called the Metric System• Also known as: International System (SI)• Based on units of 10

• Three basic Units• Meter• Liter• Gram

• Basic Prefixes:• Kilo, deca, deci, centi, milli, micro

Microscopes

• There are a few different types of microscopes• Some small: Compound Light

Microscope (We will use this a lot this year)

• Some Huge: Scanning Electron Microscopes (SEM) or Transmission Electron Microscopes (TEM)

• Both of these are about the size of a large refrigerator and can take pictures of objects at 10,000’s time magnification!

• These shoot beams of electrons on an object and an image is displayed on a computer

Other Lab Techniques

• Cell Cultures• Growing groups of cells in a

laboratory, usually all identical to each other

• Cell Fractionization• Using chemicals and blenders to

break cells into pieces in order to examine one tiny part

Something to think about