Nature of Science - Target 15

Nature of Science - Target 15

Multiple Choice

Your class is investigating the growth of plants right now. What is the BEST evidence that this investigation uses repeated trials?

• Some students are growing plants in the sunlight and some in the shade.

• Each day, the amount of water is measured and recorded.

• Every student in the classroom is growing a plant.

• Each day, the height of the plant is measured and recorded.

​Observe an experiment with repeated trials.

​Mrs. Garza’s class was divided into four groups of four students in each group. The four groups were named Red, Blue, Purple, and Orange. Each group was given six sets of the same materials. Each set contained: 1 gram of wheatgrass seeds, 1 four‐inch plant pot, and 200 grams of potting mix. The class planted a total of 24 pots of wheatgrass plants.

​The 24 plants were divided into two groups: twelve of the plants were placed on the counter and received full sunlight every day. The other twelve plants were placed in an empty cupboard with the door closed. The door was only opened to water the plants and measure the height of each plant. Data was recorded for ten days.

Multiple Choice

If we were going to repeat this investigation, what would we need to keep the same?

• Just the number of students

• Just the number of plants

• everything

• Just the number of days

​Mr. Williams class had the same number of students and was grouped the same way. Group names were the same as Mrs. Garza’s class. Mr. Williams did a teacher demonstration with the same materials, but only planted two plants. One plant was placed in on the counter in the sunlight, and one was placed in a cupboard with the door closed. Data was recorded for ten days.

​In both classrooms, an air conditioning vent blew cold air onto one side of the counter. Mrs. Garza’s twelve plants were in a line on the counter. Three of the plants were directly under the vent. Mr. Williams one plant was directly under the vent. After ten days, it was observed in Mrs. Garza’s class that the three plants under the vent didn’t grow. Turned out to be ok, because they still had nine plants that grew just fine. Their investigation was a success.

Multiple Choice

Why was Mrs. Garza's investigation a success?

• nine plants did not grow

• 1 plant did not grow

• three plants did n grow

• nine plants grew fine

Multiple Choice

What was the difference between Garza's investigation and WIlliams's investigation?

• Williams planted 24 plants while Garza planted two

• Williams only planted two plants while Garza planted 24

• They had different number of students

• Students were grouped the same way

​Mr. Williams investigation failed. His one plant was placed directly under the AC vent, and did not grow.

​One of the reasons for experiments to have repeated trials is to account for variation: not all twelve plants will grow at exactly the same rate, but across twelve plants there is enough data to say whether or not plants grow better in sunlight or dark. Another reason to have repeated trials of an experiment is to make sure the experiment is right: without repeated trials (only one plant...) something can happen to ruin the investigation.

Multiple Choice

What are the two reasons to have repeated trials in an investigation?

• To make sure the experiment is right and to make sure they are at the same rate 

• Variation and to make sure the experiment is right

​Repeated trials make sure that the results of an investigation are reliable. Mrs. Garza’s class concluded that plants grow better in the sunlight, because they had enough evidence to justify that claim. Mr. Williams class concluded that plants grow better in the dark, because that’s what their data showed. The problem is, their data wasn’t reliable, because it was based on only one plant that died in the cold air from the AC.

Multiple Choice

Repeated trials make sure the results on an investigation are ______________.

• repeated

• reliable

• empirical

• problems

Multiple Choice

A student plans and conducts an experiment to investigate the difference in the rate of growth of a plant in the sunlight compared to the shade. Which of the following would be the BEST example of an experiment with repeated trials?

• one plant in the sunlight and one plant in the shade

• two plants in the sunlight and two plants in the shade

• Three plants in the sunlight and three plants in the shade

• Four plants in the sunlight and four plants in the shade