Experiment Terms

Theory vs. Hypothesis

 A hypothesis is a proposed testable explanation for an observable phenomenon.  When a set of hypothesis is confirmed to be true many times, it is then reclassified as a theory !

Some Example Theories

 Basic theories of biology are: Cell theory : all organisms are made of cells.

Biogenesis theory : life only comes from life.

Evolution theory Gene theory and behavior.

: living things have a common ancestor and are adapted.

: Organisms contain coded information that determines their form, function,  Other Theories: Germ Theory - proposes that microorganisms are the causes of many diseases Heliocentric Theory Law of Gravity - the sun is the center of the solar system, planets revolve around the sun - masses attract each other

Practice 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 they hear bluebird songs

Control 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!



Practice 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.

Independent 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.

Independent 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.

Independent vs. Dependent Variable

 Dependent variable - what changes when the independent variable changes  the dependent variable

depends

on the outcome of the independent variable.  There can be more than one dependent variable.

Independent vs. Dependent Variable

 Example experiment : You want to measure and compare the growth rate of plants…  under full sunlight for 8 hours a day

versus

 plants that only have 4 hours of full sunlight per day.

Independent 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.

Controlled Variable

 A Controlled Variable is anything else that could influence the dependent variables.  must be carefully monitored and kept equal your experiments.

in  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.

Practice Questions

 A 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.

A 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.

A 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.

 Which of the following is a logical inference based on the contents of the graph?

A.

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.

Practice Questions

 Which variable is measured rather than manipulated? A.

Independent variable B.

Dependent variable

Practice Questions

 Positive people have more friends than negative people. Which statement is correct?

A.

The dependent variable is the positivity of the person B.

The dependent variable is the number of friends

Practice Questions

 Smoking causes lung cancer. Which statement is correct? A.

The independent variable is lung cancer B.

The independent variable is smoking