LESSON #6: TRANSPIRATIONObjectives:

Explain how transpiration occurs.

TRANSPIRATION

WHAT IS IT?Transpiration is the loss of water from a plant

- It’s caused by the evaporation of water from inside the leaves.

- The evaporation causes a slight shortage of water in the leaf, which causes it to draw more water up from the plant, which causes water to be drawn up from the roots via cohesion.

- It has two beneficial effects - a) It transports minerals from the soil and - b) It cools the plant.

FACTORS WHICH AFFECT TRANSPIRATION

The rate of transpiration is affected by

1. The amount of light2.Temperature3. Amount of air movement4.Humidity of the surrounding air

The biggest rate of transpiration occurs in hot, dry, windy, sunny conditions (ie perfect to dry clothes)

The slowest rate occurs in cool, cloudy, damp, miserable weather with no wind

WRITE A SHORT EXPLANATION WITH YOUR NEIGHBOUR:HOW DOES THE LEAF STRUCTURE HELP PREVENT EXCESSIVE WATER LOSS?

HOW DO PLANTS TRANSPORT WATER AND FOOD?

Through the Xylem and Phloem

Using capillary action:Adhesion: Surface of xylem (+ve) and water (-ve)

molecules

Cohesion: water to water

http://www.youtube.com/watch?v=mc9gUm1mMzc&feature=related

http://projects.cbe.ab.ca/resources/cts/agr1030/resources/multimedia/transpiration.swf

Transpiration virtual lab:http://www.mhhe.com/biosci/genbio/

virtual_labs/BL_10/BL_10.html

TRANSPIRATION VIRTUAL LAB:

http://www.mhhe.com/biosci/genbio/virtual_labs/BL_10/BL_10.html

1.Which factor causes the highest rate of transpiration? Why?2.Which plant has the highest rate of transpiration? Why?3.Which plant has the lowest rate of transpiration? Why?

CAPILLARY ACTION Capillary action in plants is a good example of

adhesion and cohesion.

The inner surface of the xylem contains positive and negative charges to which water forms hydrogen bonds. This is called adhesion.

As water creeps up the sides of the xylem (adhesion) the water molecules in the middle connect to other water molecules because of cohesion.

The water moves up as the water molecules at the top of the xylem enter the leaves and evaporates.

When a water molecule leaves the leaf, the molecule behind it moves up causing a general movement of the water up the tree.