GED Science TestLife ScienceMedium
A student is designing an experiment to investigate the effect of different light intensities on the rate of photosynthesis in a plant. Which of the following would be the most appropriate dependent variable to measure?
- AType of light source used.
- BRate of oxygen production by the plant.
- CAmount of water absorbed by the plant.
- DTemperature of the plant's environment.
Show answer & explanationAnswer & explanation
Correct answer: B. Rate of oxygen production by the plant.
Photosynthesis produces oxygen as a byproduct. Therefore, measuring the rate of oxygen production directly reflects the rate at which photosynthesis is occurring, making it an appropriate dependent variable.
Why the other options are wrong
- A. The type of light source is an independent variable, as it is what the experimenter changes to observe an effect.
- C. Water absorption is necessary for photosynthesis but doesn't directly measure its rate; it's also affected by transpiration.
- D. Temperature is an environmental factor that affects photosynthesis, making it a potential controlled variable or independent variable, not a dependent one.
Photosynthesis Measurement
Photosynthesis is the process by which plants convert light energy into chemical energy. Its rate can be measured by monitoring the consumption of reactants (CO2, H2O) or the production of products (O2, glucose).
- Reactants: Carbon dioxide, Water, Light energy
- Products: Glucose, Oxygen
- Oxygen production is a common proxy for rate
- Carbon dioxide uptake can also be measured
- Glucose production is harder to measure directly in real-time
Memory trick: Light makes Oxygen, so we measure the Oxygen.