Wilting & Plant Water Balance IGCSE Biology 0610

Wilting and Water Balance in Plants

Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.

Key concept

Plants wilt when water loss by transpiration exceeds water uptake by roots. Cells lose turgor pressure, becoming flaccid. Without the outward push of turgid cells against cell walls, herbaceous stems and leaves droop. Closing stomata reduces water loss but also limits photosynthesis.

Wilting links three syllabus areas: osmosis, transpiration and plant support. Strong answers explain the chain of events from excessive water loss to reduced turgor to drooping, rather than simply stating that the plant dries out.

Turgor pressure and plant support

In well-watered conditions, plant cells absorb water by osmosis. The vacuole swells, pressing the cytoplasm against the cell wall. The cell wall resists further expansion, and the cell becomes turgid. The collective outward pressure of many turgid cells supports herbaceous (non-woody) plant structures: leaves stay flat and stems stay upright.

This support mechanism is purely hydraulic. Unlike animals, herbaceous plants lack an internal skeleton. Their rigidity depends on water pressure within cells.

Why wilting happens

When transpiration exceeds water uptake: during hot, dry, or windy conditions: cells lose water faster than they can absorb it. The vacuole shrinks, the cell becomes flaccid, and turgor pressure drops. Without turgid cells pushing against cell walls, the plant wilts: leaves droop and stems become limp.

In severe cases, continued water loss leads to plasmolysis, where the cell membrane pulls away from the cell wall entirely. At this point the cell may not recover even if water is restored.

Adaptations to reduce water loss

Plants in dry environments (xerophytes) have structural adaptations to reduce transpiration: thick waxy cuticles that reduce evaporation from the leaf surface; fewer or sunken stomata that reduce the rate of water vapour diffusion; rolled leaves that trap humid air near stomata; and reduced leaf surface area (spines in cacti).

Even in temperate environments, plants close their stomata during drought. This conserves water but reduces carbon dioxide entry, which slows photosynthesis: a trade-off the plant must manage to survive.

Try a focused question (4 marks)

A potted plant wilts on a hot afternoon but recovers by the next morning. Explain why.

Show the answer and marking guidance

During the hot afternoon, transpiration rate exceeds water uptake by the roots.
Cells lose water and become flaccid, reducing turgor pressure, so the plant wilts.
At night, stomata close and transpiration decreases.
Roots continue to absorb water by osmosis, cells regain turgor and the plant recovers.

Original Cambridge-style practice written for this site. It is not an official Cambridge past-paper question.

Common mix-ups to avoid

Check these points against your own answer before moving on.

Saying the plant dries out without mentioning turgor pressure or flaccid cells.
Describing wilting as the plant dying: temporary wilting is reversible.
Confusing wilting (loss of turgor) with plasmolysis (membrane pulling from wall).
Forgetting that stomata close at night, which is why recovery often happens overnight.