For the past two weeks carbon dioxide has featured as an element in the processes of photosynthesis and respiration. Carbon dioxide enters the plant through pores in the surface of the leaves, the stomata. But stomata not only usher in carbon dioxide, they are also the exit route for water vapour.
The process of the loss of water vapour from a plant through its leaves into the atmosphere is transpiration. It’s transpiration and the transpiration pull which are responsible for the gravity defying movement of water from the roots of the plant to its very upper most parts – no matter how high rise they might be.
The water which exits the leaves as vapour is replaced by water which enters the plant via its root system. Water vapour leaving the plant creates a tension which results in liquid water being pulled up through the plant in an unbroken column of water. This is the method by which water and waterborne nutrients are circulated round the plant.
There is also control system to ensure the volume of water being absorbed by the roots remains in balance with the volume of water being lost as vapour. This control is maintained by a pair of guard cells which sit at the entrance to the stomata. If too much water is being lost through the leaves then the guard cells react, which results in the closure of the stomata. Which halts the diffusion of water vapour into the atmosphere.
So water in, water vapour out. Transpiration provides a plant with its ‘self watering’ mechanism at the same time as creating a lovely cooling effect on the leaves themselves.
{ 3 comments… read them below or add one }
Hi,
This was new and very useful information. I will start to monitor the humidity in my greenhouse to regulate this transportation of nutrients. Well done and thanks for sharing.
// Joe
Ah, another thing.
“This is the method by which water and waterborne nutrients are circulated round the plant”.
Most plants take up N from the air, this is why aerated soil is needed. This nitrogen get dissolved in the water.
Hello -Thank you for stopping by and glad you found it useful. When I first started gardening I thought of water as water – and “food” as separate – when I started to understand how the plant worked – I realised that if a plant was left short of water – it would also be left short of “food and nutrients” as well. On one level we can’t grow a plant – it has to grow itself – but I’ve certainly learnt that we can help or hinder how it grows!