▶️ Answer/Explanation
(a)(i)
Transpiration (or diffusion).
Explanation: Transpiration is the biological term for the evaporation of water from plant leaves, typically through stomata.
(a)(ii)
Comparison:
- Both groups lose mass over the 12-hour period.
- Group A (low humidity) loses significantly more water vapour (higher percentage mass loss) than Group B (high humidity). For example, A reaches ~31% while B reaches ~18%.
- The rate of loss is steeper initially for both groups but flattens out over time.
Explanation for high humidity effect:
In high humidity, there is a greater amount of water vapour in the atmosphere surrounding the leaf. This reduces the water potential gradient (or concentration gradient) between the moist air spaces inside the leaf and the outside air. Because diffusion relies on a concentration gradient, the reduced gradient results in a slower rate of water vapour loss through the stomata.
(a)(iii)
Prediction: The line should be drawn above the existing line for low humidity (Line A).
Explanation: Increasing the temperature to \(35^\circ\text{C}\) increases the kinetic energy of the water molecules, leading to a faster rate of evaporation and diffusion. Therefore, water loss would occur more rapidly and reach a higher percentage than at \(20^\circ\text{C}\).
(b)(i)
Sweat glands in the skin secrete sweat onto the skin surface. As the water in the sweat evaporates, it absorbs heat energy from the body (specifically, the latent heat of vaporisation). This removal of heat cools the blood flowing near the skin surface, helping to lower the internal body temperature back to the set point (homeostasis/negative feedback).
(b)(ii)
Expiration (breathing out).
Explanation: Air is warmed and moistened in the lungs; when humans exhale, this moisture is lost as water vapour.