Phytoplankton use sunlight to gain energy through photosynthesis. As a result of the Law of Conservation of Energy, phytoplankton cannot gain more energy than it consumes. A closed system consisting of an aquarium, phytoplankton, and sunlight is set up. Which of the following methods would best demonstrate the Law of Conservation of Energy?

Question

Phytoplankton use sunlight to gain energy through photosynthesis. As a result of the Law of Conservation of Energy, phytoplankton cannot gain more energy than it consumes. A closed system consisting of an aquarium, phytoplankton, and sunlight is set up. Which of the following methods would best demonstrate the Law of Conservation of Energy?

Measure the mass and temperature of the water. Then cover the aquarium to block the sunlight and measure the mass of the phytoplankton.
Change the closed system to isolated, so that energy can move out of it. Then measure the amount of energy that leaves.
Measure the mass of the phytoplankton before and after photosynthesis. Add the mass of the water.
Measure the amount of energy in the phytoplankton and the amount of light entering the aquarium. Then measure the amount of energy in the phytoplankton after exposure to the light and determine the difference.

Answer 1

The method that would best demonstrate the Law of Conservation of Energy in this scenario would be to measure the amount of energy in the phytoplankton before and after exposure to sunlight. By comparing the amount of energy in the phytoplankton before and after photosynthesis, it can be determined whether the phytoplankton gained energy from the sunlight or not, thus showing that the energy gained by the phytoplankton cannot exceed the energy it consumes.