2.56B - Transpiration

Edexcel IGCSE Biology

What is the definition of transpiration?

loss of water vapour from the parts of the part above ground

How does loss of water occur?

* through evaporation of water at the surfaces of the spongy mesophyll
* diffusion of water vapour through the stomata

what do the many interconnecting air spaces between the mesophyll cells and stomata create?

large surface area which means evaporation can happen rapidly when the stomata are open

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what is a transpiration stream

* movement of water in a plant
* water moves through the xylem vessels in a continuous transpiration stream from the roots to the leaves via the stem
* this is to replace the water that has been lost through transpiration

describe the relationship between the rate of transpiration from the leaves and the speed of water molecules through the xylem?

* as the rate of transpiration from the leaves **increases**…
* …water molecules are pulled up the xylem **quicker**

what are some of the functions of transpiration?

* transporting minerals
* providing water to keep cells turgid to support the structure of the plant
* providing water to leaf cells in photosynthesis
* keeping the leaves cool