ATI TEAS: Scientific Reasoning Concepts
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Overview
This chapter covers how scientists ask and answer questions. You will learn the steps of an investigation, the different types of variables, how to write a testable hypothesis, which tools and units to use for measurements, and how to draw fair conclusions from data.
An investigation usually starts with an observation and a question, followed by a hypothesis, an experiment, data collection, analysis, and a conclusion. The independent variable is what the scientist changes on purpose, the dependent variable is what is measured, and controlled variables are kept the same so the test is fair. A control group receives no treatment so the results can be compared.
Choose tools that match what you measure: a balance for mass, a graduated cylinder for liquid volume, a thermometer for temperature. A conclusion should come only from the data collected and should say whether the data support the hypothesis. Correlation, where two things change together, does not by itself prove that one causes the other.
Key concepts
Hypothesis
A testable prediction that answers a research question, often written as an if-then statement.
Memory tipIf I change X, then Y will happen.
Independent variable
The factor the scientist deliberately changes to see its effect. It is usually plotted on the x-axis of a graph.
Memory tipI change the independent variable.
Dependent variable
The factor that is measured to see how it responds to the independent variable. It is usually plotted on the y-axis.
Memory tipThe dependent variable depends on the change.
Controlled variables
Conditions kept the same across all trials so that only the independent variable could cause a difference.
Memory tipControlled = kept constant.
Control group
The group in an experiment that does not receive the treatment and serves as a baseline for comparison.
Memory tipThe control group shows what happens without the change.
Correlation vs. causation
Correlation means two things change together. Causation means one actually causes the other. A controlled experiment is needed to show causation.
Memory tipTogether does not mean because.
Often tested
- Repeating trials and using larger samples makes results more reliable.
- A hypothesis that the data do not support is still a valid result; it is rejected, not hidden.
- Use a balance for mass (grams), a graduated cylinder for liquid volume (milliliters), and a thermometer for temperature (degrees Celsius).
- A theory is a well-tested explanation; a law describes what happens, often as a formula.
Easy to confuse: Types of variables
| Variable | What it is | Example: plant growth and light |
|---|---|---|
| Independent | Changed on purpose | Hours of light per day |
| Dependent | Measured result | Plant height |
| Controlled | Kept the same | Water, soil, pot size |
3 sample questions
Verified practice questions from this unit.
Question 1. A student tests how the amount of daily sunlight affects the height of bean plants. What is the independent variable?
- ① The height of the bean plants
- ② The type of soil
- ③ The student doing the test
- ④ The amount of daily sunlight
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Answer: ④ The amount of daily sunlight
Key point: Independent variable = what is changed on purpose
The independent variable is the one the scientist changes on purpose (here, sunlight). The dependent variable is what is measured to see the effect (plant height).
Wrong choices
- The height of the bean plants: Plant height is what is measured, so it is the dependent variable.
- The type of soil: Soil should be kept the same, so it is a controlled variable.
- The student doing the test: The person doing the test is not a variable.
Question 2. Which statement is a testable hypothesis?
- ① Tomato plants are the most beautiful garden plants.
- ② If tomato plants are given more fertilizer, then they will produce more tomatoes.
- ③ Tomatoes are the tastiest vegetable.
- ④ Everyone should grow tomatoes at home.
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Answer: ② If tomato plants are given more fertilizer, then they will produce more tomatoes.
Key point: Hypothesis = testable "if…then" prediction
A hypothesis is a prediction that can be tested by an experiment, often written as "If…, then…". Fertilizer amount and number of tomatoes can both be measured, so this statement can be tested.
Wrong choices
- Tomato plants are the most beautiful garden plants.: Beauty is an opinion and cannot be measured in an experiment.
- Tomatoes are the tastiest vegetable.: Taste is an opinion, not something to test.
- Everyone should grow tomatoes at home.: This is advice, not a prediction to test.
Question 3. Researchers test whether a new pill lowers blood pressure. One group takes the new pill. Another group takes a sugar pill that looks exactly the same. Which group is the control group?
- ① The group that takes the new pill
- ② Both groups are control groups.
- ③ The group that takes the sugar pill
- ④ Neither group, because everyone takes a pill
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Answer: ③ The group that takes the sugar pill
Key point: Control group = no treatment, used for comparison
The control group does not get the treatment being tested, so it gives a baseline for comparison. Here, the group taking the sugar pill (a placebo) is the control. Any difference between the groups can then be linked to the new pill.
Wrong choices
- The group that takes the new pill: This is the experimental group, which gets the treatment being tested.
- Both groups are control groups.: Only the group without the real treatment is the control.
- Neither group, because everyone takes a pill: Taking a look-alike pill (placebo) is exactly what makes a fair control group.
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