Simple plant transpiration experiment

Transpiration is the evaporation of water from the leaves, stems or flowers of a plant.

You might have seen my transpiration experiments using celery and coloured water, and white flowers before. Today I have a slightly different way of demonstrating this important scientific concept. It's a great way to show transpiration in action, and all you need is an indoor or outdoor plant and a resealable plastic bag.

Plastic bag transpiration demonstration

You'll need

Small resealable plastic bag

Indoor or outdoor plant

Large sunflower with a small plastic bag covered one of the large leaves.

Instructions

Transpiration is faster on a hot day, so this activity is a great summer science activity.

Carefully cover either a clump of small leaves or one large leaf with the plastic bag.

Check on the bag every couple of hours.

You'll see condensation build up first, and then water will collect in the bottom of the bag.

water collected inside a small plastic bag covering a leaf

The water that has been collected in the bag is water from transpiration that has moved up the stem from the roots and also water produced during respiration.

What is transpiration?

This plastic bag transpiration demonstration shows that water was released from the leaf while it was covered up.

Transpiration is the movement of water up the stem of a plant from root to leaf when water is lost from the plant due to evaporation and diffusion of water from a plant's surface.

Water is absorbed by the root of the plant and moves through root hair cells via the process of osmosis. It then moves into the xylem vessel, which is the tube that carries the water up the stem. Water moves up the xylem vessel by adhesion (being attracted to the side of the vessel) and cohesion (water molecules being attracted to each other).

When water evaporates from the surface of the leaves, the pressure change pulls the column of water upwards to replace the water lost. This creates a constant transpiration stream of water through the plant.