Colorful Valentine's Flowers

    February, 2016: 

    Kids, Valentine’s day is right around the corner and the people who sell flowers look forward to this day all year long.  If you think about the colors of flowers you think of red, yellow, orange, pink, and white but other colors of the rainbow are not prevalent like green and blue.  Here is a way to make some of those colors appear in a flower. 

    You will need some white flowers and carnations work well – really any stemmed plant will work. 

    First, trim the flowers at the stalks.  Fill a vase or jar with water and add some food coloring of your choice (green or blue?).  Put your flowers in the water and wait.  Usually you can see effects within a few hours!

    The science:

    The reason this happens is because of something called the transpiration stream. This 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 occurring at the leaves. Firstly water is absorbed by the root 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 plant. Plants are not like us with pumping mechanism that pushes our blood around, so water moves up the vessel by adhesion (being attracted to the side of the vessel) and cohesion (water molecules being attracted to each other – think of water molecules as people who are holding hands and as one person climbs up the side of a wall, they pull another along with them). Therefore when water evaporates from the top of the leaves it changes the pressure in the vessel and pulls up the column of water to replace the water lost.

    The best way to consider this is to imagine you have a thick shake – the straw can’t carry the shake up, but if you withdraw air from the top, you change the pressure and force the liquid shake up the straw where there is less pressure. It moves in a column because the molecules are attracted to each other.

    This is similar to a ChemShorts article from August 1993


    Paul Brandt