Capillary Action In Plants

blueflower Capillary action is vital to life processes and is the name given to the way that water moves through things.  This is an intriguing science project for even the Littlest Sparks, which demonstrates the movement of water through plants.

For this science project you will need:

  • A small bunch of white carnations.
  • Food dye of various colours – we always like to include blue though because so few flowers are truly blue!
  • Some clear containers.
  • Sharp scissors or secateurs to cut the stems off your carnations.  (Adult assistance required!)
  • Water

What to do:

  • Fill your containers with water and add a different coloured food dye to each one.  Put lots of food dye in if you want to seed dramatic results!  It is not possible to add too much dye for this experiment.
  • The ends of the carnation stems need to be cut diagonally at an angle, this helps them to absorb water.
  • Place a carnation in each of your containers containing the coloured water.
  • Watch and observe really carefully over the next few days.  Which dye is the fastest to change the colour of the flower?  Look really closely, does all of the flower change colour?

What happened here?

blueflowerinvase The surfaces of plants are covered in thousands of little holes called stomata.  Water evaporates from these holes to keep the plant cool. This is called transpiration.  (See our Pint Pot Planet experiment.)

As water leaves the plant it causes more to be ‘sucked up’ either from the ground through roots or in this case from the vase of coloured water through the stem.

The stem can do this easily for two reasons and it is all to do with water being ‘sticky’.

In the first instance this happens because water molecules like to stick together, so water molecules follow each other up the stem.  Imagine hundreds of children holding hands and dragging each other through a tunnel, as one child pops out of the end more are dragged through!

The way in which water likes to stick to itself is called water cohesion, sometimes we also call this surface tension.

Secondly plants are of full of tiny tunnels called xylem, and water likes to stick to these surfaces too, making it easy for the water to travel through the plant.  Could you spot them when you looked at your dyed flowers?

Take it further:

Repeat this experiment but instead of using carnations use a stem of celery.  Can you see how the food dye has moved through the plant using capillary action?  Capillary action is just for plants either!  Fill a flower pot with dry compost.  Now stand it in a deep saucer of water.  Capillary action will cause the water to travel to the surface of the compost and make it wet.  (This is a very good way to water your seedlings by the way!)  You can also use some absorbent kitchen towel to watch capillary action.  Fill a small container with water, you can add food dye if you wish, hold the kitchen towel upright with one corner dangling in the water and watch how the water moves up the kitchen towel – it’s capillary action in action again!

Don’t forget to visit all of our kids science experiements.

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