1. Your experiment tests whether your hypothesis is true or false.
You should also repeat your experiments several times to make sure that the first results weren't just an accident.
The scientific method starts when you ask a question about something that you observe: How, What, When, Who, Which, Why, or Where?
A hypothesis is an educated guess about the answers to those questions.
you will communicate your results to others.
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2. Scientists use an experiment to search for cause and effect relationships in nature….
“if this changes, then what else changes?”
The changing quantities are called variables.

3. The independent variable is the one that is changed by the scientist.
The scientist focuses his or her observations on the dependent variable to see how it responds to the change.
For example, if you open a faucet wider and wider, the quantity of water flowing changes in response.
Which variable is independent?
Which variable is dependent?

4. Experiments also have controlled variables
Experiments also have controlled variables. Controlled variables are quantities that a scientist wants to remain constant as he changes one thing at a time.

5. In a good experiment, the scientist must be able to measure the values for each variable, whether it is independent (how wide the faucet is opened) or dependent (how much water comes out.
Weight or mass or time or distance are examples of variables that are very easy to measure.
In the following question, identify the independent, the dependant and the controlled variables.

6. Which question are the students most likely trying to answer?
A group of students set up 2 compost piles (A & B) that contain the same amount & type of dead organic material. Both piles are sheltered from rain. Twice a week the students add water to pile A, but add no water to pile B. Once a week the students estimate the numbers of different types of organisms in each pile by random sampling.
Which question are the students most likely trying to answer?
Do more organisms live in compost piles with moist environments or dry environments?
How does the number of carnivores in a compost pile affect the number of omnivores?
How does the moisture level in a compost pile change over time?
What types of organic material leads to the most diverse compost pile food webs?
TAKS 1 TEKS BIO 2A

7. Graphs are very good ways to display your variables.
The dependent variables are graphed on the vertical axis.
It’s very important to read all graph labels, including the title, to understand the variables and their measurements.

8. Solubility Curve of Potassium Nitrate, KNO3
Concentration of KNO3 (g/100 g H2O)
Temperature (oC)
A saturated solution of potassium nitrate (KNO3) is prepared in 100 grams of water heated to 60oC. About how many grams of KNO3 will have settled out of the solution once it reaches a room temperature of 24oC?
30 g
65 g
95 g
145 g
TAKS 4 TEKS IPC 9D

9. Data tables are also used to record and compare variables.

10. F. Bacteria multiply most slowly at 200C.
The data table shows the growth rates of bacteria during an investigation. Based on the data, which of the following conclusions would be valid?
F. Bacteria multiply most slowly at 200C.
G. Bacteria multiply most rapidly at 350C.
H. Bacteria multiply most rapidly at 400C.
J. Bacteria multiply most slowly at 450C
Growth rates of Bacteria
Temperature (degrees Celsius)
Time for the population to double (minutes) 10
133 15 66 20 36 25 30 35 40 16
TAKS 1 TEKS BIO 2D

11. On the TAKS test, you will be tested over your knowledge of how to design and carry out a scientific experiment.
So what are the steps in planning and implementing a valid experiment?
Dictionary Help: VALID means acceptable, or legitimate, trustworthy.
Dictionary Help: IMPLEMENTING means doing the experiment, taking the steps to make it happen.

12. Asking questions: Can you look at an experimental set-up and figure out what question the scientist was trying to answer? Look for clues in the drawing or paragraph! What are they measuring? What does the data tell you?
The diagram shows an experimental setup. Which of these questions was this experiment designed to answer?
A Does water boil when exposed to air?
B Will fire turn a gas into a liquid?
C Does air expand when heated?
D Will heat turn a gas into a solid?
Air
Heat

13. Formulating Testable Hypothesis
Can you recognize a valid hypothesis? Can you create one?
Is it a statement that you can prove with data?
Is it testable?
What question might these students be trying to answer?
What hypothesis might these students write to test their question?

14. Is the experiment valid?
Factors affecting the validity (trustworthiness) of the experiment
A control group is used
The hypothesis has measurable variables (“Flowers grown indoors will have the ‘best’ smell,” is not a measurable variable!)
Sample size is large enough. You have to run lots of test over and over again to get reliable results
Only one variable is tested at a time! “Will limiting sunlight and water effect plant growth?” is not a valid question!

15. READ CAREFULLY!
The table shows the time it took trees of the same type and size to drop all of their leaves after being grown in different atmospheres. For the experiment to be valid, which of these must be a constant for all the trees?
F The height of all the trees during the entire experiment
G The amount of water available to all trees during the experiment
H The mass of fallen leaves collected from each tree
J The rate of photosynthesis in all trees during the experiment
Dependent variable
All of the independent variables but one (gases added) must remain constant for the experiment to be valid.
Dependent variable
Dependent variable

16. Selecting the correct procedure and equipment:
Sometimes you will be asked to select correct equipment or the correct procedure from a particular lab set-up.
Which procedure is best to use when determining the density of a rock?
F Place the rock in a water-filled beaker and find the height at which the rock floats above the water.
G Use a ruler to measure the rock’s dimensions and then find its mass using an analytical balance.
H Measure the mass of the rock on a balance and then find the volume of water it displaces in a graduated cylinder.
J Place the rock in three liquids with different known densities and observe which liquid the rock floats in.
Formula Chart to the RESCUE!!!!