Transpiration

If we look at the water cycle, we know that evaporation is the process where water changes it's state of matter to a vapour and rises up through the sun "drying" it out. This then turns into a cloud, and that cloud gets heavier and precipitates. It rains.

Now, excess water in plants and trees do a similar thing. They release excess water from their stomata, which in turn is soaked up by the sun in a similar process to evaporation. This is called transpiration.

The majority of the water retained in the plants are not used for growth or their metabolism, so while it is retained, it can be easily lost through transpiration.

What About Translocation?

Inside the plant, a process called translocation happens. This is where the excess water is moved about the plant. It travels within the phloem, which is like a vein within the plant to allow movement of nutrients and sugars and other liquids.

Phloem are cells, each with a semi-permeable membrane, that are bunched together to form tubes, and it's along these tubes that the water and sugars travel. Because phloem allow for transport both ways, it can travel in any direction around the plant. Depending on where the sugars are going, they can be dropped off at any point, or they can be stored within the plant somewhere until needed.

Xylem's Role

A xylem tube is a longer hollow tube that runs alongside the phloem, and is strengthened with lignin. It provides a direct access between the roots and the leaves for water and mineral ions that can then be used in photosynthesis.

Types of Transpiration

There are different types of transpiration, depending on the location in the plant. They include:

• stomatal - evaporation from the plant's stomata
• cuticular - evaporation from the plant's cuticle
• lenticular - evaporation from the plant lenticels, small openings in the bark branches and twigs

Here is a YouTube video from Cognito about Transpiration & Translocation: