Final answer:
Light/dark bottles measure primary productivity by comparing dissolved oxygen levels in two bottles, one exposed to light and one not, to determine the rates of photosynthesis and respiration in the water sample. The option (A) is correct.
Step-by-step explanation:
Light/dark bottle experiments are a method used in aquatic biology to measure primary productivity, which is the rate at which organisms like phytoplankton produce organic compounds from carbon dioxide and water through photosynthesis. In this method, two bottles are used: one is exposed to light (light bottle), and the other is kept in the dark (dark bottle) to prevent photosynthesis.
By comparing dissolved oxygen levels in both bottles after a certain period, scientists can determine the net and gross primary productivity of the aquatic environment. This is because oxygen production during photosynthesis will occur in the light bottle, while the dark bottle will only reflect oxygen consumption through respiration. Therefore, the correct answer to what light/dark bottles are measuring is not light intensity, temperature, ultraviolet radiation, or heat conductivity, but rather the amount of photosynthesis and respiration occurring in the water sample. Therefore, option (A) is correct.