Transpiration Stream Diagram IGCSE Biology 0610

Transpiration Stream Diagram: Water Movement Through 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 diagram

The transpiration stream is the continuous movement of water from root hair cells, through xylem vessels, to the leaves where it evaporates from the spongy mesophyll surfaces and diffuses out through stomata.

The transpiration stream diagram shows the path water takes from soil to atmosphere through the plant. Questions test whether students can describe each stage and explain the factors that affect the rate of transpiration.

Drawing the complete pathway

Draw a simplified plant with roots, stem and leaves. Use arrows to trace water movement: (1) water enters root hair cells by osmosis from the soil; (2) water passes from cell to cell across the root cortex; (3) water enters the xylem vessels in the centre of the root; (4) water moves up through the xylem in the stem; (5) water enters the leaf through the xylem in the vascular bundle; (6) water evaporates from the surface of spongy mesophyll cells into air spaces; (7) water vapour diffuses out through open stomata.

What drives the stream

Transpiration: the loss of water vapour from the leaves: creates a pull on the water column in the xylem. As water evaporates from the mesophyll surfaces, it is replaced by water drawn up from below. This creates a continuous stream. The water molecules are held together by cohesion, which allows the column to be pulled upward without breaking.

Factors affecting transpiration rate

Four factors affect the rate: temperature (higher temperature increases kinetic energy and evaporation rate), humidity (lower humidity increases the diffusion gradient for water vapour), wind speed (faster wind removes water vapour from around the leaf, maintaining a steep gradient), and light intensity (more light causes stomata to open, increasing water loss).

A potometer measures water uptake, which is used as an estimate of transpiration rate.

Wilting and the role of guard cells

When water loss exceeds water uptake, cells lose turgor and the plant wilts. Guard cells close the stomata to reduce water loss, but this also reduces carbon dioxide entry and slows photosynthesis. In the diagram, show stomata as open when guard cells are turgid and closed when guard cells are flaccid.

Label checklist

Check these labels are present and correctly positioned before finishing your drawing.

✓ Root hair cells
✓ Root cortex
✓ Xylem vessels
✓ Stem
✓ Leaf vascular bundle
✓ Spongy mesophyll air spaces
✓ Stomata
✓ Guard cells
✓ Arrows showing water movement direction

Try a diagram question (4 marks)

Describe the pathway taken by a water molecule from the soil to the atmosphere. [4]

Show the answer and marking guidance

Water enters the root hair cell by osmosis through the partially permeable membrane.
Water passes across the root cortex and into the xylem vessels.
Water moves up through the xylem in the stem to the leaf.
Water evaporates from the spongy mesophyll cell surfaces into air spaces and diffuses out through the stomata.

Original Cambridge-style practice written for this site.

Common diagram mistakes

Check these against your own drawing before moving on.

Saying water is "sucked up" instead of describing transpiration pull.
Forgetting that water evaporates inside the leaf before diffusing out.
Not mentioning osmosis when describing water entry into root hair cells.
Drawing arrows going in both directions in the xylem: water in xylem moves upward only.