GAS EXCHANGE IN PLANTS 2.39 understand gas exchange (of carbon dioxide and oxygen) in relation to respiration and photosynthesis

CO2 and O2 diffuse in and out of leaves through stomata.

CO2 is used in photosynthesis and produced by respiration, whereas O2 is used in

respiration and produced in photosynthesis!

Photosynthesis & Respiration2.39 understand gas exchange (of carbon dioxide and oxygen) in relation to respiration and photosynthesis

Both processes run all the time. So the net amount of glucose the plant produces (i.e. the amount it gets to use for growth etc) is governed by the formula;

Net Glucose = Total production – Amount used in respiration

The Compensation Point is defined as;

0 = Total production – Amount used in respirationOr

Photosynthesis = Respiration

Light Intensity & Gas Exchange2.40 understand that respiration continues during the day and night, but that the net exchange of carbon dioxide and oxygen

depends on the intensity of light (TA)

The amount of glucose the plant uses in respiration in nearly constant.

However, glucose production by photosynthesis is not.

It is dependent on the rate-limiting factors (i.e. light intensity, CO2 level, water availability, temperature etc).

At night photosynthesis is virtually zero. (Net Carbon Dioxide production)

In the day the photosynthesis is large. (Net Oxygen production)

Light Intensity &

Gas Exchange2.40 understand that respiration

continues during the day and night, but that the net exchange of carbon dioxide and oxygen depends on the intensity of

light (TA)

Leaf Structure and Photosynthesis 2.41 explain how the structure of the leaf is adapted for gas exchange

In sunlight the guard cell becomes turgidTurgid guard cells open the stomaIncreases gas exchange

Low light causes guard cells to become flaccidFlaccid guard cells close the stomaDecreases water loss

Stomata and Gas Exchange 2.42 describe the role of stomata in gas exchange

Stomata and Gas Exchange 2.42 describe the role of stomata in gas exchange

Exp1

Exp 2

Potometer1) You must cut the shoots under water and you must assemble the

potometer under water. If air gets into the xylem vessels of the plant, it can form air locks which will prevent the plant taking up water and so prevent steady transpiration.

2) Check all seals are airtight – coat seals with Vaseline jelly

3) The potometers should be left for the leaves to dry. Alternatively \dry the leaves gently with a paper towel. The potometer will not work properly until any excess water on the leaves has evaporated or been removed.

4) Adding food colouring to the water makes it easier to see the air bubble in the capillary tube.

Stomata and Gas Exchange 2.42 describe the role of stomata in gas exchange

Stomata and Gas Exchange 2.42 describe the role of stomata in gas exchange

Experiment to Know 2.43 describe experiments to investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator (TA)

An experiment which will show the effect of light intensity on the rate of gas exchange. - Seal two leaves (still attached to the plant) in separate plastic bags with

some bicarbonate indicator solution.

- One of the bags is black and the other is translucent.

- The leaf in the black bag produces CO2 via respiration and the colour of the bicarbonate indicator changes quickly to yellow. - The leaf in the translucent bag produces O2 via photosynthesis and the bicarbonate indicator solution changes to red slowly.

Bicarbonate Indicator colours:Red in the absence of CO2

Yellow in the presence of CO2