xylem – Dr. How's Science Wows

What is transpiration?

Transpiration is the process whereby water is taken into a plant by the roots, transported up through the plant and released from the leaves as water vapour!

Lets learn more!

Transpiration is a bit like perspiration (sweating) in humans – it helps to keep the plant cool! As the water vapour transpires out of tiny holes (called stomata) fresh water is drawn up from below. This means there is always an unbroken tower of water running from the bottom to the top of the plant at all times. Water travels up the plant through tubes called Xylem.

The constant flow of water through the xylem tubes of the plant is called the transpiration stream; this stream keeps the stem firm so that it can support the weight of the plant.

Plants put roots down into the soil to draw water and nutrients up into the plant.

Daintree Rainforest: Image source Wikimedia Commons

‘Did you know… trees and plants in rain forests help to make rain; if a forest is cut down the area around it may suffer from drought!’

Transpiration accounts for up to 10% of water in the atmosphere! Some trees can loose hundreds of thousands of litres of water in a single day through transpiration! The water vapour trees transpire into the air cools the air!

How powerful is transpiration?

photo credit: Christopher Chan via photopin cc

Transpiration can lift water all the way to the top of the tallest trees!

Stromata

Stomata are tiny holes or pores on leaves, stems and even petals of the plant that allow water out of the plant (transpiration) and gases (like carbon dioxide) into the plant. Most of the stromata of a plant are found on the underside of the leaves.

Stomata can open and close to control the amount of water leaving the plant or the amount of gas coming in.

An experiment to try at home: Tracking the flow of water!

You will need…. white flowers, clear cups and food colouring of your choice

Step 1: Fill cups 2/3 full with water

Step 2: Add different food colouring to each one; I used blue, yellow, green, red
(Note: you need a fair amount of food colouring… at least half a bottle per cup)

Step 3: Cut the stem of four flowers to desired length then add one to each cup

Step 4: Leave for a few hours (or overnight) and see what has happened!

So what has happened?…The coloured water travels up the stem and eventually reaches the flower where it changes the flower’s colour.

What could you change or what other things could you try?… What would you change if you repeated this experiment? You could try it using a variety of different types of flowers to see if one type works better than another. You could vary the amount of food colouring you use.