Mr. Brown's Science Labs

Maya keeps a tray of radish seedlings on the classroom windowsill. She notices that the seedlings closest to the window look taller than the seedlings near the back of the tray. Maya wonders whether light is the reason. Her scientific question is: Does the number of hours of light a radish plant receives each day affect how tall it grows?

Before testing anything, Maya writes a hypothesis, which is a testable answer to a scientific question. She predicts that if radish plants receive more hours of light each day, then they will grow taller, because plants use light to make their own food.

Next, Maya plans a fair test. The one factor she changes on purpose is the number of hours of light each group receives. That factor is the independent variable. The factor she measures is the height of the plants in centimeters. That factor is the dependent variable. Everything else has to stay the same: the same kind of seed, the same amount of water, the same soil, the same size pot, and the same room temperature. Those factors are the controlled variables. Without them, Maya could not tell which factor caused the change she saw.

Maya sets up four groups of plants and gives each group 2, 6, 10, or 14 hours of light per day. She grows three plants in each group instead of only one. Repeating a test this way is called replication, and it helps a scientist decide whether a result is reliable or whether it happened by chance.

After 14 days Maya measures every plant and records her data, which are the measurements and observations collected during an investigation. She then makes an inference, an explanation based on evidence, and writes a conclusion that answers her original question using that evidence.