1.3 - Investigating photosynthesis

Which of the following is essential for the process but not a reactant in photosynthesis?

• light

• carbon dioxide

• water

A student is planning to investigate photosynthesis. Select a suitable statement to explain her hypothesis.

• Plants need light for photosynthesis.

• Only the green parts of a plant carry out photosynthesis.

• Photosynthesis needs light, so if the intensity of light changes, then the rate of photosynthesis should change too.

A student's hypothesis is that light intensity affects the rate of photosynthesis. Which idea would be the most suitable way to test this hypothesis using the apparatus shown?

• Change the distance and see how that affects the temperature of the water.

• Change the distance and see how that affects the number of bubbles produced by the pondweed in 2 minutes.

• Change the type of plant and see how that affects the number of bubbles produced by the pondweed in 2 minutes.

What is the independent variable (the thing you change) in this investigation?

• distance from the lamp to the pondweed

• number of bubbles of oxygen produced in 2 minutes

• temperature of the water

What is the dependent variable (the thing you measure) in this investigation?

• distance from the lamp to the pondweed

• number of bubbles of oxygen produced in 2 minutes

• temperature of the water

Which of the following variables could affect the number of bubbles produced in 2 minutes?

• light in the room other than the lamp

• all of the variables

• the temperature of the water

• the surface area of the pondweed

In this investigation, you plan to investigate five different distances. Which values would be most suitable?

• 2, 4, 6, 8 and 10 cm

• 10, 20, 30, 40 and 50 cm

• 30, 35, 40, 45 and 50 cm

Use the image to determine the distance measurement (in cm) from the lamp to the pondweed in the position shown.

• 30

• 20

• 25

The measurements in the table have been repeated three times. Why should you repeat measurements?

• to make it easier to spot anomalies

• to test a different range of values for the independent variable

• to be able to work out mean results

Which variable should you plot on the x-axis of your line graph?

• distance from the lamp to the pondweed (cm)

• number of bubbles of oxygen produced in two minutes