So you have some white flowers but actually wouldn’t they look good with a bit of red in them? Or maybe blue? Not only are they pretty but can be used to demonstrate transpiration.
How could you do this? Well with what looks like a little bit of magic and a huge dollop of science!
Food colouring – we’ve found Wilton gel colours work well. Natural food colourings DO NOT work in our experience.
Small jar or vase
Trim the flowers at the stalks.
Fill as vase or jar with water and add some food colouring of your choice.
Put your flowers in the water and wait.
Usually you can see effects within a few hours!
This one is yellow and black.
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 (we will look at this another day!). 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). 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 it, but if you suck from the top, you change the pressure and force the shake up the straw. It moves in a column because the molecules are attracted to each other.