Question

a scientist hypothesizes that increased carbon dioxide levels will lead to increased plant growth. which of the following would be a valid way to test this hypothesis?
measure the carbon dioxide levels in different plant species.
research existing data on plant growth and carbon dioxide levels.
grow two groups of the same plant species, one with normal carbon dioxide levels and one with increased levels, and compare their growth.
observe plants growing in different natural environments.
which of the following best defines a hypothesis?
a well - substantiated explanation of some aspect of the natural world.
a detailed record of measurements and data collected during an investigation.
a summary of the results of an experiment.
a tentative explanation for an observation that can be tested.
students observe that a ball rolls downhill. which of the following is a logical inference?
the ball will eventually stop.
gravity is pulling the ball downwards.
the hill is made of grass.
the ball is round.

Explanation:

For the first question, to test the hypothesis about carbon dioxide and plant growth, a controlled experiment (growing two groups of the same plant species with different CO₂ levels) is valid as it isolates the variable. Measuring CO₂ in different species doesn't test the growth - CO₂ relationship. Researching existing data may not be specific to this hypothesis. Observing in natural environments has too many variables.
For the second question, a hypothesis is a tentative explanation (not a well - substantiated theory like in the first option, not data record or experiment summary).
For the third question, an inference is a conclusion based on reasoning. "Gravity is pulling the ball downwards" is an inference about the cause of the ball rolling. "The ball will eventually stop" is a prediction. "The hill is made of grass" and "The ball is round" are observations.

Answer:

1. Grow two groups of the same plant species, one with normal carbon dioxide levels and one with increased levels, and compare their growth.
2. A tentative explanation for an observation that can be tested.
3. Gravity is pulling the ball downwards.