Trace water from root hair to mesophyll
Follow the required sequence through uptake, root tissues, long-distance transport and leaf delivery.
Section B8.2 · Water uptake
Cross-referenced to the 2028–2029 0653 section using original teaching from the related single-science courses. A 0653-specific objective-by-objective and Core/Supplement review is in progress. Written practice is self-checked and does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall root tissue positions and leaf mesophyll.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which region surrounds the central root transport tissue?
What you will learn
- Put the four required regions in order
- Distinguish cell-to-cell root movement from the xylem stream
Begin at the absorbing cell
Water enters root hair cells from soil solution and moves across the root cortex towards xylem. Root hair and cortex are different parts of the route: the first is an epidermal-cell extension, while the second is internal root tissue.
Water then travels through xylem in the root and stem towards leaf veins. The required sequence is root hair cells → root cortex cells → xylem → mesophyll cells. The arrows show the pathway, not a claim that every step has the same transport mechanism.
Delivery is not the final loss step
Water moves from leaf xylem towards mesophyll cells. Some is used or retained, and some evaporates from moist mesophyll surfaces before water vapour exits through stomata. Delivery to mesophyll and loss as vapour are related but distinct parts of the account.
Do not insert phloem as the principal water-uptake route merely because it also contains solution. For the described transpiration stream, use xylem. Stomata are leaf openings after the mesophyll delivery stage, not channels carrying soil water along the root.
Sources for this lesson
Pause and explain
Which order is correct for this pathway?
Worked example
Order mesophyll, root cortex, xylem and root hair for the stated water pathway.
Show the worked solution
- Start with the absorbing root hair, then cross cortex.
- Move into xylem, then to leaf mesophyll.
Answer Root hair → root cortex → xylem → mesophyll.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Write the four required water-pathway regions in order.
Give me a hint
Start with the soil-facing cell extension.
Compare my reasoning
- Write root hair and root cortex first.
- Follow with xylem and mesophyll.
Root hair → root cortex → xylem → mesophyll.
Look for these in your work
- Include all four regions
- Put them in the correct order
Explain why “water goes directly from root hair into leaf mesophyll” omits important stages.
Give me a hint
Which root tissue and long-distance tissue are missing?
Compare my reasoning
- Water crosses the root cortex.
- Xylem carries it over the root/stem-to-leaf distance.
The statement omits root cortex and the xylem transport pathway.
Look for these in your work
- Name cortex
- Name xylem and its role
A dye reaches leaf veins before surrounding leaf tissue. Explain how this can support the route without proving every root-cell mechanism.
Give me a hint
Match the observation to the part of the plant tested.
Compare my reasoning
- Vein arrival supports an above-ground xylem pathway.
- A cut-shoot observation omits root hair and cortex entry.
The observation supports xylem delivery in the shoot; it does not demonstrate the mechanisms across root hair and cortex cells.
Look for these in your work
- Use the observed delivery evidence
- State the root-mechanism limit
Common mistakes
- Placing phloem in the stated xylem water route.
- Putting stomata between the root hair and cortex.
What can you explain now?
Which order is correct for this pathway?
Compare with the explanation
Root hair → cortex → xylem → mesophyll
This follows uptake to leaf delivery.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Trace the route aloud, then add what happens to some water after mesophyll delivery.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.