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Potometer and Rates affecting Transpiration

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by

Shahnaz Malik

on 20 November 2013

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Transcript of Potometer and Rates affecting Transpiration

Homework
Write out all the factors affecting the rate of transpiration, from page 13, and write the correct explanation next to it.
Starter
Explain why water loss from the leaves of a plant is unavoidable?

Give three benefits of transpiration to plants.

Describe the cohesion-tension theory.

What is the term used to describe the attraction of water to the surface of the xylem vessels?


How could you compare the results from two separate experiments?
Set up in same
environmental
conditions
Calculate the
rate
per unit area of leaf
Run for the same
length of time
Pick
the plants at the same time, etc

Activity
Learning Objectives
TRANSPORT IN PLANTS
Potometer and factors affecting the rate of transpiration
To describe how to measure transpiration using a potometer, and to explain what factors affect the rate of transpiration.
Plenary
Do the past paper questions.

Measuring transpiration in a lab
A
potometer
is used to measure transpiration
BUT really measures uptake of
water
by the plant.



It is assumed that water uptake is directly related to water loss from the leaves as 99% of water taken up is lost in transpiration.

Use these words to fill in the blanks.
Slant
Temperature
Scale
Air
Healthy
Airlocks
Dry
Under
Air / Water
Acclimatise
Distance
Time

cut shoot water
Answers
Factors affecting the rate of transpiration
These can either be to do with the plant or its environment.

Anything that increase the water vapour potential gradient between the inside and outside of the leaf will increase water loss.

Activity
Match the factors with its explanation, on
page 13.

Use numbers to match.
Feature that affects
the rate of water loss.

How it affects water loss.

Number of leaves

More leaves larger surface area over which vapour can be lost

Number size, position
of stomata

Many large stomata, water vapour lost more quickly. Stomata on lower surface, water vapour loss is slower

Presence of cuticle
Waxy cuticle reduces evaporation from leaf surface
Light

Stomata open to allow gaseous exchange for photosynthesis
Temperature

Higher temperature will increase rate of water loss:
Increase rate of evaporation from cell surface so water vapour potential in leaf rises
Increase rate of diffusion through stomata as water molecules have more kinetic energy
Decrease relative water vapour potential in the air, allowing more rapid diffusion of molecules out of leaf

Relative humidity

Higher relative humidity in air will decrease rate of water loss – smaller water vapour potential gradient between air spaces in leaf and outside.

Air movement or wind

Air moving outside of leaf will carry away water vapour that just diffused out of leaf. This will maintain a high water vapour potential gradient.

Water availability

If there is little water in the soil, then plant can not replace the water that is lost. Water loss in plants is reduced when stomata are closed or when the plants shed leaves in winter.

insert into apparatus under water
under

full of water/no extra bubbles/no
airlocks
cut shoot at a
slant
off leaves
dry
ensure tight joints
air / water
allow time to
acclimatise
keep condition(s)/named condition(s)
constant e.g.
temp
introduce an bubble

air

measure moved per unit time
distance
shut screw clip
ref. to ; e.g. note where bubble
is at start
scale
Due:
21/11/2013
Full transcript