In this activity, students see capillary action . . . in action! Watch coloured water flow up a celery stalk, showing just how water moves from the roots of plants to their leaves.
All plants need water to survive. Plants use water to carry nutrients to their roots, stems, leaves and flowers and to prevent them from drying out and wilting.
How does a plant move water from the ground up into the rest of the plant?
Just as humans have veins and arteries that move blood around inside the body, plants have xylem to move water. This is the plant’s water transportation system. You’ve probably seen old xylem tissue—the rings on a tree trunk. Xylem tissues live for one year, then die, leaving a ring between the old and new xylem.
Xylem tissue is made of millions of tiny tubes made of cellulose. Because water molecules like to stick together (cohesion) and like to stick to the walls of the tubes of cellulose (adhesion), they rise up the tubes all the way from the roots to the leaves. Water then evaporates from the leaves, helping to draw up more water from the roots. This process is called capillary action.
Celery is handy for demonstrating capillary action because it has a lot of xylem tubes in the stalk, making for fast water uptake. You’ll see the pale green leaves take on a reddish and bluish colour because the dissolved food colouring moves with the water through the xylem tubes into the celery stalk and leaves. The water evaporates through the leaves (transpiration) and deposits the colour in the plant. This helps pull more water into the plant to keep the xylem tubes filled, continuing the cycle of water uptake.