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Igcse biology edexcel 2.39 2.43

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Edexcell ppt Biology 2.39-2.43

Used in lessons to scaffold class teaching and as a revision resource for students

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Igcse biology edexcel 2.39 2.43

  1. 1. 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!
  2. 2. Photosynthesis & Respiration 2.39 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 respiration Or Photosynthesis = Respiration
  3. 3. Light Intensity & Gas Exchange 2.40 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)
  4. 4. Light Intensity & Gas Exchange 2.40 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)
  5. 5. Leaf Structure and Photosynthesis 2.41 explain how the structure of the leaf is adapted for gas exchange
  6. 6. Stomata and Gas Exchange 2.42 describe the role of stomata in gas exchange In sunlight the guard cell becomes turgid Turgid guard cells open the stoma Increases gas exchange Low light causes guard cells to become flaccid Flaccid guard cells close the stoma Decreases water loss
  7. 7. Stomata and Gas Exchange 2.42 describe the role of stomata in gas exchange Exp 1 Exp 2
  8. 8. Stomata and Gas Exchange 2.42 describe the role of stomata in gas exchange Potometer 1) 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. 1) 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. 2) Adding food colouring to the water makes it easier to see the air bubble in the capillary tube.
  9. 9. Stomata and Gas Exchange 2.42 describe the role of stomata in gas exchange
  10. 10. 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

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