Transport in Plants - Capillary Action

Have you ever wondered how water is transported up the stem of a plant against gravity? This transportation process is called transpiration. You can demonstrate transpiration easily with simple transpiration experiments.

You might also like our plant respiration and photosynthesis investigations.

Transport in Plants - Transpiration

Transpiration occurs when water on the surface of leaf cells evaporates and then diffuses out of the leaf. This draws water out of the xylem cells inside the leaf to replace the evaporated water. Xylem cells form a continuous tube from the leaf to the roots, which acts like a drinking straw, giving a flow of water from root to leaf.

Transport in Plants - Capillary Action

Transpiration helps another process called capillary action to take place, which is how water moves through a plant.

Water molecules are attracted to the molecules of the inside of the stem. It is this attraction which helps force the water up from the ground and around the plant.

Transpiration Experiment

You can demonstrate capillary action and transpiration by placing a flower in a glass of coloured water. After a few hours, the petals will turn the same colour as the water. This is because the coloured water is transported up the stem and into the petals.

Transpiration Definition

Transpiration is the movement of water through a plant and evaporation from leaves, stems and flowers.

Water moves through the xylem vessels of a plant in a continuous transpiration stream.

root - stem - leaf

Functions of Transpiration - transport in plants

Transport of mineral ions

Transport of water to all parts of the plant, including leaf cells where it is needed for photosynthesis.

Keeping leaves cool as water evaporates from the surface.

What factors affect transpiration?

There are three forces involved in this process of transporting water in plants.

Adhesion allows water to stick to the organic tissues of a plant.

Cohesion keeps the water molecules together.

Surface tension holds the water molecules together as they are transported through the plant.

Capillary Action Definition

Capillary action is the movement of a liquid through a narrow space caused by cohesion, surface tension, and adhesion.

For capillary action to work, the adhesion force between the water and plant tissues must be stronger than the cohesion between water molecules.

When a water molecule is more attracted to the plant, it is pulled towards the plant tissue, but as water molecules are highly attracted to each other, the first molecule brings further water molecules with it.

Plants use two different transport systems, both of which are rows of cells that form tubes around the plant. The xylem transports water and minerals from the roots to the leaves, while the phloem moves food substances from the leaves to the rest of the plant.

Plant Stem Model

We used straws to make a very simplified model of a plant stem. The xylem is the centre yellow part, and the phloem is the blue straws.

Easy capillary action experiment

This simple experiment is a super easy and fun demonstration of capillary action and water transport in plants.

Materials

Tray

Water

Paper - sugar paper works best

Scissors

Method

Cut out several flower shapes from the sugar paper.

Curl up the edges and place on the surface of the water.

Watch as the flower opens up.

How does capillary action work?

Paper is made of many fibres. As they absorb water, they swell, and the paper expands, allowing the flower shape to open up.

This process is called 'capillary action'. Water uses this process to move along the tiny gaps in the fibres of the paper. This occurs because the adhesive force between the water and the paper is stronger than the cohesive forces inside the water itself. This is the same process by which water travels from the root up the stem to the petals of a plant.

More transpiration experiment ideas

The DK Website has some great plant facts for kids.

We also used two syringes to show water travelling up the stem of a LEGO plant, which is quite a nice model for younger children.

Suitable for Key Stage 2 Science

Plant Science

Investigate the way in which water is transported within plants

Last Updated on March 25, 2025 by Emma Vanstone