Advanced Science Primary 4 Systems

A scientist blocked the stomata on all the leaves of a well-watered plant by coating them with petroleum jelly. She also cut off all the roots. After two days, which observation would BEST explain why the plant wilted?

A Water could not enter the plant because the roots were removed, and water could not leave through the blocked stomata, so water pressure inside the plant dropped.
B Water could not enter the plant because the roots were removed. Even though the stomata were blocked, water already inside the plant was used up by the cells and not replaced, causing the plant to wilt.
C Water could not leave the plant because the stomata were blocked, so the plant became waterlogged and wilted.
D The blocked stomata prevented carbon dioxide from entering the plant, stopping photosynthesis and causing the plant to wilt immediately.
Show Worked Solution

Worked Solution

Step 1: Identify the two changes made — roots removed (no water uptake) and stomata blocked (no transpiration/gas exchange). Step 2: Roots are the main organ for absorbing water from the soil. Without roots, no new water enters the plant. Step 3: Blocking stomata reduces water loss through transpiration. This actually helps the plant conserve water. Step 4: However, cells inside the plant still use water for metabolic processes. Over two days, the existing water supply is consumed and not replenished (because roots are gone). Step 5: When water inside the cells is used up and not replaced, cells lose turgor pressure and become flaccid. The plant wilts. Conclusion: The primary cause of wilting is the absence of roots preventing water intake, not the blocked stomata.

Correct answer: Water could not enter the plant because the roots were removed. Even though the stomata were blocked, water already inside the plant was used up by the cells and not replaced, causing the plant to wilt.

Want more questions like this? Superholic Lab has 10,000+ MOE-aligned questions with full worked solutions.

Start Free Trial — 7 Days Free