Final answer:
A potometer measures the water uptake by a plant due to transpiration, correlating this with the rate of water loss through the stomata on the leaves. The correct answer is 'a) By measuring the rate of transpiration and correlating it with water uptake'.
Step-by-step explanation:
A potometer measures the rate of water uptake by a plant, which is largely due to the process of transpiration. Transpiration is the loss of water from the plant through evaporation at the leaf surface. This process is driven by the evaporation of water from the stomata on the leaves, which are tiny pores that open and close to regulate gas exchange and water loss.
The main way a potometer shows that water taken up by the plant is indeed lost through the ventral surfaces of the leaves is by measuring the rate of transpiration and correlating it with water uptake. Therefore, the correct option is a) By measuring the rate of transpiration and correlating it with water uptake.
The operation of a potometer is based on the principle that as water is lost from the leaves through the stomata, it creates a negative pressure that draws more water into the plant from the roots. The water potential decreases from the roots to the leaves, aiding in this upward movement.
By observing the movement of water through the potometer, one can infer the rate of transpiration occurring. While there are methods that involve isotope-labeled water or analyzing oxygen concentration, these are not directly related to the function of a potometer.