Explain why a plant wilts when loss exceeds uptake
Connect a water imbalance with reduced cell turgor and temporary changes in support.
Exam scope and assessment notes
Extended only (Supplement) · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall osmosis, vacuoles and turgor.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is turgor?
What you will learn
- Relate uptake/loss imbalance to cell water loss
- Explain wilting using reduced turgor
An imbalance reduces stored water
A plant can lose water faster than roots replace it. When the loss exceeds uptake, available water in tissues declines. Over a stated interval, the water balance is uptake minus loss; a negative balance means a reduction in water stored, assuming no other inputs or outputs in the simplified model.
For uptake of 3 mL and loss of 5 mL, the balance is −2 mL. This does not mean that transpiration is negative; it means the plant’s stored water decreases by 2 mL in the stated model.
Less turgor means less support
Cells lose water, their vacuoles become less full and the pressure of contents against cell walls decreases. Reduced turgor weakens support in soft tissues, so leaves and young stems can droop: the plant wilts. This is different from destroying lignified xylem walls.
Recovery is possible if water supply restores turgor before lasting damage occurs, but not guaranteed after severe stress. Wilting alone does not uniquely diagnose its cause; damaged roots or other changes can also reduce uptake. Use the stated water balance to explain this case.
Pause and explain
Which chain explains this wilting case?
Worked example
Uptake is 3 mL and loss 5 mL. Explain the balance and the link to wilting.
Show the worked solution
- 3 − 5 = −2 mL, a fall in stored water in the simplified balance.
- Cell water/turgor decreases, reducing support in soft tissues.
Answer A 2 mL water deficit can reduce turgor and cause wilting under the stated conditions.
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.
Calculate water balance for uptake 3 mL and loss 5 mL.
Give me a hint
Use uptake minus loss.
Compare my reasoning
- 3 − 5 = −2.
- Interpret the negative sign as reduced stored water.
−2 mL: stored water decreases by 2 mL in the simplified model.
Look for these in your work
- Calculate −2 mL
- Interpret the sign correctly
Uptake and loss both equal 4 mL over the interval. Does this balance itself prove wilting?
Give me a hint
Compare the totals, then the limit of the model.
Compare my reasoning
- 4 − 4 = 0 mL change in stored water from these flows.
- Zero net change alone does not establish reduced turgor or wilting.
No. The stated flows balance; this evidence alone does not prove a new water deficit or wilting.
Look for these in your work
- Calculate the zero balance
- Avoid an unsupported wilting claim
A wilted seedling regains firmness after watering. Explain a plausible cellular change and one limit.
Give me a hint
Use water, vacuole and turgor rather than new wood formation.
Compare my reasoning
- Water entry restores fuller vacuoles and turgor.
- Recovery here does not guarantee all severe wilting is reversible.
Restored cell water increases turgor and soft-tissue support; severe damage may prevent recovery in other cases.
Look for these in your work
- Explain restored turgor
- State the recovery limit
Common mistakes
- Treating reduced turgor as broken cell walls.
- Promising complete recovery from any degree of wilting.
What can you explain now?
Which chain explains this wilting case?
Compare with the explanation
Loss exceeds uptake → less cell water → reduced turgor
Reduced turgor weakens soft-tissue support.
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Make it stick
Explain wilting from water balance to the cell and then to the visible leaf.
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.