In a typical aquatic plant experiment (e.g., Elodea), which measurement provides a direct estimate of the rate of photosynthesis under controlled light and temperature conditions?

• A. Measure the decrease in soil mineral nutrients around the plant over time
• B. Measure the amount of chlorophyll present in the leaves once at the end of the experiment
• C. Measure the rate of water uptake by the plant over time
• D. Measure oxygen production over time (e.g., volume of $O_2$ released or bubbles per minute)

Answer: (D)

Verified step by step guidance

1. Understand that photosynthesis is the process by which plants convert light energy into chemical energy, producing oxygen (O\_2) as a byproduct.
2. Recognize that measuring oxygen production directly reflects the photosynthetic activity because oxygen is released during the light-dependent reactions of photosynthesis.
3. Note that other measurements, such as soil mineral nutrient decrease or chlorophyll content, do not directly quantify the rate of photosynthesis; nutrient levels change due to various factors, and chlorophyll amount is a static measure, not a rate.
4. Consider that water uptake rate is related to transpiration and not a direct measure of photosynthesis rate, even though water is a reactant in photosynthesis.
5. Therefore, to estimate the rate of photosynthesis under controlled conditions, measure the volume or number of oxygen bubbles produced over time, as this provides a direct and quantifiable indicator of photosynthetic activity.