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Photosynthesis by Ms.Wong GCE O/L Gr10

This presentation is exclusively based on Sri Lankan GCE O/L exams for Grade 10 &11 students.However this can also be beneficial for other students who wish to know more about science.

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Photosynthesis by Ms.Wong GCE O/L Gr10

  1. 1. Photosynthesis Ms.Wong BAMS(UG) Lesson 02
  2. 2. Lesson Overview:  2.1Factors that affect photosynthesis ◦ Testing Factors essential for photosynthesis  2.2 Products of photosynthesis ◦ Testing products of photosynthesis  2.3 Importance of photosynthesis
  3. 3. What is Photosynthesis?  Production of glucose in the plant cells of green leaves of plants by using water and carbon dioxide in the presence of sunlight and chlorophyl pigment.
  4. 4. Diagrammatic Representation of Photosynthesis
  5. 5. Factors that affect photosynthesis  Accordingly, the factors that affect photosynthesis are,  Chlorophyll -Present in the palnt leaves in chloroplast  Light energy - from the sunlight  Water -Taken from the soil via root hairs  Carbon dioxide -taken through stomata from the atmosphere
  6. 6. Products of photosynthesis  The glucose (C6 H12O6 ) produced during photosynthesis will be temporarily stored in leaves as starch  Later, part of that starch is converted into sucrose (C12H22O11) and transport into other tissues, via phloem  The sucrose that is transported to storing organs are again stored as starch  E.g :-Fruits,Vegetables,Yams, Leaves, Roots  The byproduct of photosynthesis is O2 and it is diffused into the atmosphere through stomata.
  7. 7. Test for starch  Glucose produced during photosynthesis is stored temporarily in leaves as starch  Therefore it could be tested whether the photosynthesis has taken place or not by doing a test for starch
  8. 8. Test to identify starch
  9. 9.  As chlorophyll dissolve in alcohol, the leaf is boiled in an alcohol solution  Then the solution becomes green in colour and leaf turns to pale colour  As alcohol is highly inflammable, it is boiled in a water bath  If the leaf turns to blue or dark purple, once iodine is added, we can conclude that starch is present in the leaf
  10. 10.  The covered area of leaf A has not received light energy  Therefore photosynthesis has not taken place  Hence, there was no colour change with iodine solution  The covered area of leaf B with colourless polythene has received light energy  Therefore photosynthesis has taken place and showed a colour change to dark purple or blue indicating starch has been produced  Accordingly, we can conclude that light energy is necessary for photosynthesis
  11. 11.  KOH present in bag D absorbs CO2  Therefore leaf D does not do photosynthesis as it does not receive CO2  Therefore there is no colour change  Leaf C receives CO2, so it photosynthesises  Therefore a colour change can be observed  Leaf D has not produced starch but leaf C has produced starch  Accordingly it can be concluded that CO2 is necessary for photosynthesis
  12. 12.  The white colour regions lack chlorophyll, so photosynthesis has not taken place  Therefore starch has not been produced  So it can be concluded that chlorophyll is essential for photosynthesis
  13. 13.  Gas bubbles release from the aquatic plant and that gas gets collected at the top of the boiling tube  After the accumulation of gas about 3/4 th of its volume, the tube will be taken out and a glowing splinter is inserted to test whether the gas is oxygen  The splinter will burn with a bright flame  So we can conclude that the gas given out in photosynthesis is oxygen
  14. 14. 2.3 Importance of photosynthesis  Light energy is converted to chemical energy during photosynthesis  Plants produce food and all organisms live on earth depend directly or indirectly on that food  Photosynthesis cannot be done artificially  Therefore this process carried out by green plants is essential for the maintenance of life on earth  The oxygen gas which is required for the survival of aerobic organisms and combustion of materials is released mainly by photosynthesis  Carbondioxide that is accumulated due to respiration and combustion is removed from the environment by photosynthesis  Thereby it helps to maintain O2 and CO2 balance in the atmosphere  Photosynthesis helps to maintain the carbon cycle

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