Biology – Homeostasis in plants | e-Consult
Homeostasis in plants (1 questions)
Experimental Design:
Independent Variable: Light intensity (e.g., measured in lux or µmol m⁻² s⁻¹). The student would manipulate the amount of light reaching the leaves.
Dependent Variable: Rate of transpiration. This is the rate at which water is lost from the leaves through the stomata. This would be measured using a suitable method (see below).
Control Variables: These are factors that must be kept constant across all experimental groups to ensure that only the light intensity is affecting transpiration. Examples include:
- Temperature: Maintain a constant temperature throughout the experiment.
- Humidity: Maintain a constant humidity level in the surrounding air.
- Air movement: Control the amount of air movement around the leaves (e.g., using a fan with a consistent speed or by conducting the experiment in a still environment).
- Leaf type: Use leaves from the same plant species and ideally from the same plant to minimize variation in leaf structure.
- Leaf size/area: Select leaves of similar size and area.
Measuring Transpiration Rate: The rate of transpiration can be measured using several methods:
- Potometer: A potometer is a device that measures the rate of water uptake by a plant. A small section of stem is placed in a sealed tube filled with water. The amount of water that rises in the tube over a set period is measured.
- Hydrometers: A small, accurately weighed leaf disc is placed in a container of water. The water level in the container rises, and the amount of water displaced is proportional to the amount of water lost through transpiration.
- Transpiration Weighing: The entire plant or a portion of it is weighed before and after a period of exposure to light. The difference in weight represents the water lost through transpiration.
Expected Results and Support for the Role of Light:
The student would expect to observe a positive correlation between light intensity and the rate of transpiration. As light intensity increases, the rate of transpiration should also increase, up to a certain point. This is because increased light stimulates stomatal opening, allowing for greater CO2 uptake and, consequently, increased water loss through transpiration.
These results would strongly support the role of light in stomatal opening. The experiment demonstrates that light is a key environmental signal that triggers the physiological processes leading to stomatal opening. The increased light energy drives the activation of light-sensitive receptors, leading to the influx of potassium ions into the guard cells and the subsequent opening of the stomatal pores. This allows for increased CO2 uptake for photosynthesis, which is essential for plant growth and survival.