Wei Lin placed a leafy plant in a transparent plastic bag and sealed it tightly. She left it in sunlight for four hours. She then placed an identical plant (same species, same size) in a sealed bag but covered the entire bag with black cloth. After four hours, she compared the droplets of water inside each bag. Which statement BEST explains why Bag A (sunlight) had more water droplets than Bag B (dark)?
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Worked Solution
Step 1: Identify the key variable — Bag A is in sunlight, Bag B is in darkness. All other conditions are the same.
Step 2: Sunlight provides light energy but also raises the temperature around the plant in Bag A.
Step 3: Transpiration is the process by which plants lose water vapour mainly through stomata. The rate of transpiration increases with temperature and light intensity.
Step 4: In Bag A, higher temperature (from sunlight) and open stomata (in response to light) both increase the rate of transpiration. More water vapour is released from the leaves into the sealed bag.
Step 5: This water vapour condenses on the cooler inner surface of the bag, forming more water droplets.
Step 6: In Bag B, there is no warmth from sunlight and stomata may close in darkness, so transpiration rate is lower, resulting in fewer droplets.
Conclusion: More water droplets in Bag A are due to increased transpiration driven primarily by the warmth and light conditions from sunlight.
Correct answer: Bag A had more water droplets because the warmth from sunlight increased the rate of transpiration in the plant, causing more water to evaporate from the leaves.
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