Transpiration

?
  • Created by: nellbob
  • Created on: 19-02-17 18:51

Transpiration

What is transpiration?

Transpiration is where a plant absorbs water by it's roots and then give off water vapour through the pores in the leaves. 

More info...

  • Water on the surface (inside the leaf) of the spongy and palisade cell layers evaporate and then diffuse out of the leaf. This is transpiration.
  • Water is drawn out of the xylem leaves to replace what is lost through transpiration.
  • The xylem cells make a long continuous 'drinking straw' shape to create a flow of water and ions from roots to leaves. This movement is called a transpiration stream.
  • Leaves contain tiny stomata on their surface to allow carbon dioxide from the air to enter, and also for water vapour to exit through the pores. 
1 of 2

Measuring Transpiration/Factors

We measure transpiration using a potometer. As water moves up through the plant, the air bubble moves along the scale - giving a measure of water absorbed by the plant over time and thus the transpiration rate.We can create many conditions to see how the factors affect the plant and rate of transpiration:

  • Temperature (heat lamp) - an increase in the temperature warms the water in the leaves causing it to evaporate more quickly, and also increases the capacity of air to absorb more water.
  • Sunlight (sun - window/lamp) - same effect as temp. because of warmed leaves. Causes stomata to open and thus a higher transpiration rate to that of a cold day.
  • Wind (fan/hairdryer) - transpiration relies on diffusion. In windy conditions the air molecules are blown away from the leaves preventing air around the leaves becoming saturated with water molecules.
  • Humidity - lows transpiration. This is the concentration of water vapour in the air. Low humidity = low concentration and a good concentration gradient which helps the transport of water by diffusion. High humidity = air around leaves is already saturated and a higher concentration of water molecules than inside the leaves. (SEE BBC BITESIZE FOR A GOOD TABLE)
2 of 2

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Photosynthesis and transpiration resources »