ATI TEAS Scientific Reasoning Summary

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.

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.

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.

A graduated cylinder is tall and narrow with fine markings, so it measures liquid volume more precisely than a beaker. Read it at eye level at the bottom of the curved surface (the meniscus).

Wrong choices

• Beaker: Beaker markings give only rough estimates of volume.
• Balance: A balance measures mass, not volume.
• Thermometer: A thermometer measures temperature.

Mass is measured in grams (g) or kilograms (kg) in the metric system. An apple has a mass of a few hundred grams, so grams are a good fit.

Wrong choices

• Liters: Liters measure volume.
• Meters: Meters measure length.
• Degrees Celsius: Degrees Celsius measure temperature.

Controlled variables are kept the same so that only the independent variable changes. If the amounts of sugar or water changed between trials, you could not tell whether temperature caused the difference.

Wrong choices

• The water temperature: Water temperature is the independent variable, so it must change.
• The time it takes the sugar to dissolve: Dissolving time is the dependent variable, the result being measured.
• The results of each trial: Results are what you measure; you cannot set them ahead of time.

Look at the change between readings:

1. 0 → 2 min: 110 − 72 = 38
2. 2 → 4 min: 128 − 110 = 18
3. 4 → 6 min: 130 − 128 = 2

The rises get smaller and smaller, so the heart rate climbed quickly and then leveled off.

Wrong choices

• Heart rate rose by the same amount every 2 minutes.: The increases were 38, then 18, then only 2.
• Heart rate went down as jogging went on.: Every reading is higher than the one before.
• Jogging had no effect on heart rate.: Heart rate rose from 72 to 130.

A common order is:

1. Observe
2. Ask a question
3. Form a hypothesis
4. Test it with an experiment
5. Analyze the data
6. Draw a conclusion and share results

Wrong choices

• Draw a conclusion.: A conclusion comes after the experiment and data analysis.
• Ask a question.: Asking a question comes before forming a hypothesis.
• Make an observation.: Observation usually starts the process.

A fair test changes only one variable. Here both fertilizer and light were different, so the extra growth could come from the sunlight, the fertilizer, or both. Both plants should get the same light, and only the fertilizer should differ.

Wrong choices

• Plant B should also have been given fertilizer.: Then there would be nothing to compare; the control should not get fertilizer.
• Plant height cannot be measured.: Height can easily be measured with a ruler.
• The student should have used a thermometer.: Temperature is not the main problem here.

Two things can be linked (correlated) without one causing the other. People who smoke are more likely to carry lighters and more likely to get lung cancer. Smoking is a third factor (confounding variable) that explains the link.

Wrong choices

• Carrying a lighter causes lung cancer.: The study shows a link, not a cause; lighters themselves do not cause cancer.
• Lung cancer causes people to carry lighters.: This reverses cause and effect without any support.
• The finding proves that the study was done incorrectly.: The link can be real; it just has another explanation.