Unit 1: Introduction to Biology & Biochemistry

Variables Life is continually changing because life has many variables. Variables are things that are apt to change. The temperature, humidity, and other environmental factors change regularly. We can think of these things as variables. What’s more, these variables can effect different aspects of your life.

Variables The weather can effect your clothing decisions. If it’s hot and sunny, you might wear shorts and sandals. If it’s cold and rainy, you might wear a sweater and rain boots. Variables can drastically effect the outcome of an experiment. Therefore, it is important to control all variables that are not being tested.

Example You are trying to figure out how to make an orange tree grow faster. You run an experiment and use different types of soil and different types of fertilizer with four orange trees. Some of the trees grew faster than others. What cause the tree to grow faster?

Example Cont. It could have been the soil OR the fertilizer. It could have been a combination of the two. You cannot tell for sure because you changed more than one thing.

Solution It’s important to remember that, when running an experiment, everything must be the same (constants) except for the one thing that you are testing (variable).

Types of Variables Independent Variable: the variable you choose to change/what you are testing Goes on x-axis when graphing data Example: amount of water given to plants Dependent Variable: the variable that changes in response to what you are testing Goes on y-axis when graphing data Example: heights of plants

Types of Variables Constant Variables: all other factors that MUST stay the same throughout the experiment Example: amount of sunlight, type of soil, brand of fertilizer, type of seeds used, number of seeds used

Example You are testing the effect of different types of fertilizer on plant growth. Identify the independent variable and the dependent variable.

September 11, 2015 A student wonders, “Does the moisture content in soil affect how far a worm can dig?”. Identify the variables that are being considered in this experiment and the variables that need to be controlled. Independent Variable: _____________________ Dependent Variable: _____________________ Controlled Variable(s): _____________________

September 11, 2015 The idea of a control group is not the same as a controlled variable. Suppose a scientist is doing an experiment to determine the effect of an all-organic diet on the occurrence of cancer in rats. What variables should the scientist control in the experiment? Describe the control group for this experiment. Why is it important for a scientist to sue a control group when working with organisms in an experiment?

Hypothesis A hypothesis is a proposed explanation made at the beginning of an investigation. It is based on limited information and is a starting point in your experiment. Hypotheses are written as “If… then…” statements. They also include the independent and dependent variables.

Hypothesis Format: “If independent variable, then dependent variable”.

September 14, 2015 What types of graphs are there? When organizing your data, how do you know which one to use?

September 17, 2015 Think back to your graphing lab, what sources of error were there? In other words, if there were errors in your experiment, where did they stem from?