2Theory vs. HypothesisA hypothesis is a proposed testable explanation for an observable phenomenon.When a set of hypothesis isconfirmed to be true manytimes, it is then reclassifiedas a theory!
3Some Example TheoriesBasic theories of biology are: Cell theory: all organisms are made of cells. Biogenesis theory: life only comes from life. Evolution theory: living things have a common ancestor and are adapted. Gene theory: Organisms contain coded information that determines their form, function, and behavior.Other Theories: Germ Theory - proposes that microorganisms are the causes of many diseases Heliocentric Theory - the sun is the center of the solar system, planets revolve around the sun Law of Gravity - masses attract each other
4Practice Question Which is NOT a valid hypothesis? A. Bluebirds sing to attract mates.B. Bluebird songs are beautiful.C. Only male bluebirds sing.D. Sparrows will leave territories where theyhear bluebird songs
5Control group vs. experimental group Control group – provides a normal standard to which the experimental group can be compared. It is CONSTANT!Experimental group – experimental group consists of what is being MANIPULATED!
7Practice Question The purpose of including a control in a scientific investigation is to provide what?a. A basis for comparison.b. A correction for experimental errors.c. A preliminary trial of the methods.d. An opportunity for repetition of the experiment.
8Independent vs. Dependent Variable Used in an experiment to keep track of what's going on.Used to measure your results and draw accurate conclusions.Are related to one another.
9Independent vs. Dependent Variable Independent variable – what you change in order to do your experiment.There should be only one independent variable for any valid experiment.
10Independent vs. Dependent Variable Dependent variable - what changes when the independent variable changesthe dependent variable depends on the outcome of the independent variable.There can be more than one dependent variable.
11Independent vs. Dependent Variable Example experiment: You want to measure and compare the growth rate of plants…under full sunlight for8 hours a dayversusplants that only have4 hours of full sunlight per day.
12Independent vs. Dependent Variable Independent variable – the amount of time per day of full sunlight (you control this!)Dependent variable - the growth rate of the plants.
14Controlled VariableA Controlled Variable is anything else that could influence the dependent variables.must be carefully monitored and kept equal in your experiments.Example: Could the amount of water affect the growth of our plants?Yes, so you need to make sure that each plant gets the same amount of water in the experiment.In this way you eliminate water as a possible source of difference between your plants.
15Practice QuestionsA researcher investigated two groups of fruit flies.Population A was kept in a 0.5 L container.Population B was kept in a l.0 L container.Below is a graph showing the growth of these two populations.
16A researcher investigated two groups of fruit flies. Population A was kept in a 0.5 L container.Population B was kept in a l.0 L container.What is the manipulated (independent) variable?A. The number of flies.B. The time in days.C. The numbers of groups studied.D. The size of the containers.
17A researcher investigated two groups of fruit flies. Population A was kept in a 0.5 L container.Population B was kept in a l.0 L container.What is the dependent variable?A. The number of flies.B. The time in days.C. The numbers of groups studied.D. The size of the containers.
18Which of the following is a logical inference based on the contents of the graph? The flies in Group B were healthier than those in Group A.B. A fly population with more available space will grow larger than a population with less space.C. If Group B were observed for 40 more days, the size of the population would double.D. In 40 days, the sizes of both populations would decrease at the same rate.
19Practice Questions Which variable is measured rather than manipulated? Independent variableDependent variable
20Practice Questions Positive people have more friends than negative people. Whichstatement is correct?The dependent variable is the positivity of the personThe dependent variable is the number of friends
21Practice Questions Smoking causes lung cancer. Which statement is correct?The independent variable is lung cancerThe independent variable is smoking