Lesson 11 of 12 / Nutrition and transport in flowering plants
When a plant wilts
Why can a plant droop even while its roots are taking up water?
I can explain wilting by comparing water loss, water uptake and cell turgor.
I can investigate and explain four environmental effects on transpiration and wilting.Syllabus
Syllabus K224 / K225, Topic 8(k). Investigate and explain four environmental effects on transpiration and wilting.
About 5 min
Make a guess. You are not marked.
A plant's roots are still taking up water, yet its leaves droop. How can that be?
Show the answer
It loses water faster than it gains it.
Wilting depends on the balance. When loss exceeds uptake, cells lose turgor and soft parts droop.
The key idea
If water loss exceeds uptake, cells lose water and turgor. Soft tissues become flaccid and the plant wilts.
Loss 7 > uptake 4: a deficit of 3 arbitrary units per hour. Cells lose water and turgor, so soft tissues can wilt.
Blue: vacuole. Olive outer line: cell wall. The selected state contrasts turgor qualitatively, without implying that ordinary wilting requires plasmolysis. The illustrative rates do not predict an exact cell size or recovery time.
Stomatal closure reduces further water loss but restricts CO2 entry. Recovery is possible if tissues remain undamaged; severe stress may cause lasting harm.
Explanation
A plant takes in water and loses water at the same time. If it loses water faster than it takes it in, its cells lose water. Hot, dry or windy weather makes this more likely, especially when the soil is dry.
When cells lose water, their vacuoles shrink and the cell contents press less hard against the cell wall. This pressure is called turgor. With less turgor, soft parts such as leaves and young stems droop. The plant wilts.
When the plant is short of water, its stomata may close. This saves water, but it also stops carbon dioxide getting in, so photosynthesis slows down.
If the plant later takes in more water than it loses, its cells take in water by osmosis, become firm again and the plant stands up. If the plant was short of water for too long, it may not recover.
Step by step
- 1
Compare the two rates
Do not infer water balance from uptake alone.
- 2
Explain the cell change
Connect water loss to reduced vacuole volume and pressure against the wall.
- 3
Connect cell to whole plant
Lower turgor reduces support in soft tissues, producing wilting.
Worked example
Uptake continues
An illustrative plant takes up 4 units of water per hour but loses 7. Explain why it can wilt despite continued uptake.
One way to explain it
It loses 3 more units per hour than it replaces, so tissues have a net water deficit. Cells lose water and turgor, making soft tissues flaccid and causing drooping.
Why this answer works
- Compare both rates: 7 is greater than 4.
- Link the deficit to cellular water loss.
- Explain turgor rather than saying only "the plant is dry".
Watch out for this
A student says: "A plant cannot wilt unless water uptake falls to zero." What is wrong with this?
Show the answer
Wilting can occur whenever water loss exceeds uptake sufficiently. Both processes can still be occurring.
Check your understanding
Which chain best explains wilting?
Show the answer
Loss exceeds uptake -> cells lose water -> turgor falls -> soft tissues droop.
This links the whole-plant imbalance to the cell-level mechanism and visible effect.
Quick recall
Why can a plant droop even while its roots are taking up water?