Transport in Plants: Question 1
Syllabus 8.2
A student plants a young sunflower seedling in moist soil. Some of the water taken up by the roots eventually reaches cells inside a leaf, where it evaporates.
Which row shows the correct order of the structures that this water passes through, from the soil to the leaf?
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Worked solution
Step 1: Identify where water enters the plant
Water in the soil first enters the plant through the root hair cells. These cells have a large surface area, which speeds up the uptake of water and mineral ions from the soil. This rules out any order that starts somewhere else.
Step 2: Follow the pathway across the root
After entering a root hair cell, water crosses the root by passing through the root cortex cells before it reaches the centre of the root, where the xylem tissue is found.
Step 3: Follow the pathway up to the leaf
Once inside the xylem, water travels upward through the stem and into the leaf. There it passes into the mesophyll cells, from whose surfaces it evaporates into the air spaces of the leaf before diffusing out through the stomata.
Step 4: Why the other options are wrong
- B swaps the first two stages, as if water reached the cortex before the root hair cells.
- C puts the xylem before the root cortex cells, skipping the crossing of the cortex.
- D reverses the entire pathway, sending water from the leaf back down to the root.
Final answer
The correct order is root hair cell → root cortex cell → xylem → mesophyll cell, option A.