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  1. 1. <ul><li>Define terms photosynthesis. </li></ul><ul><li>The process of photosynthesis. </li></ul><ul><li>Light-dependent photosynthesis. </li></ul><ul><li>Light-independence photosynthesis. </li></ul><ul><li>Factors affecting the rate of photosynthesis. </li></ul>PHOTOSYNTHESIS
  2. 2. OBJECTIVES: <ul><li>By the end of the lesson, student should be able to : </li></ul><ul><li>Define terms photosynthesis. </li></ul><ul><li>Understand the process of photosynthesis. </li></ul><ul><li>Identify the stages of photosynthesis. </li></ul><ul><li>Understand some factors affecting photosynthesis. </li></ul>
  3. 3. <ul><li>The process of converting light energy to chemical energy and storing it in the bonds of sugar. </li></ul><ul><li>This process occurs in plants and some algae (Kingdom Protista). </li></ul><ul><li>Plants need only light energy, CO 2 , and H 2 O to make sugar. </li></ul>WHAT IS PHOTOSYNTHESIS?
  4. 4. <ul><li>The process of photosynthesis takes place in the chloroplasts, specifically using chlorophyll, the green pigment involved in photosynthesis. </li></ul>
  5. 7. <ul><li>A commonly used but slightly simplified equation for photosynthesis is: </li></ul><ul><li>carbon dioxide + water + light energy -> glucose + oxygen </li></ul>6 CO 2 (gas) + 12 H 2 O(liquid) + photons C 6 H 12 O 6 (aqueous) + 6 O 2 (gas)
  7. 9. <ul><li>The thylakoid is the structural unit of photosynthesis. </li></ul><ul><li>Both photosynthetic prokaryotes and eukaryotes have these flattened sacs/vesicles containing photosynthetic chemicals. </li></ul><ul><li>Only eukaryotes have chloroplasts with a surrounding membrane. </li></ul>CHOLOROPLAST
  8. 10. <ul><li>Thylakoids are stacked like pancakes in stacks known collectively as grana. </li></ul><ul><li>The areas between grana are referred to as stroma. </li></ul><ul><li>While the mitochondrion has two membrane systems, the chloroplast has three, forming three compartments. </li></ul>CHOLOROPLAST
  9. 11. <ul><li>The specialized membrane structures in which photosynthesis takes place. </li></ul><ul><li>Internal membranes in the chloroplast where the light reaction chemicals are embedded. </li></ul><ul><li>Collections of thylakoids form the grana. </li></ul>CHOLOROPLAST
  10. 12. <ul><li>Photosynthesis occurs in two stages . </li></ul><ul><li>In the first phase, light-dependent reactions or photosynthetic reactions (also called the Light reactions ) capture the energy of light and use it to make high-energy molecules. </li></ul><ul><li>During the second phase, the light-independent reactions (also called the Calvin-Benson Cycle, and formerly known as the Dark Reactions ) use the high-energy molecules to capture carbon dioxide (CO 2 ) and make the precursors of carbohydrates. </li></ul>STAGES OF PHOTOSYNTHESIS:
  11. 13. <ul><li>In the Light Dependent Processes (Light Reactions) light strikes chlorophyll a in such a way as to excite electrons to a higher energy state. </li></ul><ul><li>In a series of reactions the energy is converted (along an electron transport process) into ATP and NADPH. </li></ul>LIGHT - DEPENDENT
  12. 14. <ul><li>Water is split in the process, releasing oxygen as a by-product of the reaction. </li></ul><ul><li>The ATP and NADPH are used to make C-C bonds in the Light Independent Process (Dark Reactions). </li></ul>
  13. 15. <ul><li>In the Light Independent Process, carbon dioxide from the atmosphere (or water for aquatic/marine organisms) is captured and modified by the addition of Hydrogen to form carbohydrates (general formula of carbohydrates is [CH 2 O]n). </li></ul><ul><li>The incorporation of carbon dioxide into organic compounds is known as carbon fixation. </li></ul>LIGHT - INDEPENDENT
  14. 16. <ul><li>The energy for this comes from the first phase of the photosynthetic process. </li></ul><ul><li>Living systems cannot directly utilize light energy, but can, through a complicated series of reactions, convert it into C-C bond energy that can be released by glycolysis and other metabolic processes. </li></ul>
  15. 18. <ul><li>Photosynthesis may simply be defined as the conversion of light energy into chemical energy by living organisms. </li></ul><ul><li>It is affected by its surroundings and the rate of photosynthesis is affected by the concentration of carbon dioxide , the intensity of light , and the temperature. </li></ul><ul><li>Each factor affects a different rate-limiting step. </li></ul>FACTORS AFFECTING:
  16. 19. <ul><li>As light intensity increases, the photosynthetic rate increases until a point is reached where the rate begins to level off. </li></ul><ul><li>At low light intensity, photosynthesis occurs slowly because only a small quantity of ATP and NADPH is created by the light dependent reactions. </li></ul>LIGHT INTENSITY
  17. 20. <ul><li>As light intensity increases, more ATP and NADPH are created, thus increasing the photosynthetic rate. </li></ul><ul><li>At high light intensity, photosynthetic rate levels out, not due to light intensity but due to other limiting factors, including competition between oxygen and carbon dioxide. </li></ul>
  18. 21. LOW CONC . HIGH CONC.
  19. 22. <ul><li>As carbon dioxide concentration increases, the rate of photosynthesis increases. </li></ul><ul><li>At high concentrations, the rate of photosynthesis begins to level out due to factors not related to carbon dioxide concentration. </li></ul>CO2 CONCENTRATION:
  20. 23. <ul><li>One reason might be that some of the enzymes of photosynthesis are working at their maximum rate. </li></ul><ul><li>In general, carbon dioxide is found in low concentration in the atmosphere, and so atmospheric carbon dioxide levels may be a major limiting factor on photosynthesis when at low levels. </li></ul>
  21. 24. LOW CONC . HIGH CONC.
  22. 25. <ul><li>As temperature increases above freezing, the rate of photosynthesis increases. </li></ul><ul><li>This occurs because molecules are moving more quickly and there is a greater chance of a collision resulting in a chemical reaction. </li></ul><ul><li>At some point, a temperature is reached that is an optimum temperature. </li></ul>TEMPERATURE
  23. 26. <ul><li>The photosynthetic reaction rate is at its quickest rate at this point. </li></ul><ul><li>Above that temperature, the enzymes begin to denature (as in RUBP carboxylase), slowing the rate of photosynthesis until a temperature is reached where photosynthesis does not occur at all. </li></ul>
  24. 27. LOW CONC . HIGH CONC.