Photosynthesis

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Photosynthesis

  1. 1. Photosynthesis
  2. 2. Energy for life processes <ul><li>  Energy is the  ability to do work </li></ul><ul><li>Work for a cell includes  growth & repair, active transport across cell membranes, reproduction, synthesis of cellular products </li></ul><ul><li>Autotrophs or producers convert sunlight, CO2, and H2O into glucose (their food) </li></ul><ul><li>Plants, algae, and blue-green bacteria, some prokaryot es, are producers or autotrophs </li></ul><ul><li>Only 10% of the Earth’s 40 million species are autotrophs </li></ul><ul><li>Other autotrophs use  inorganic compounds instead of sunlight  to make food; process known as  chemosynthesis </li></ul><ul><li>Producers  make food for themselves and heterotrophs  (consumers that cannot make food for themselves) </li></ul><ul><li>Heterotrophs include  animals, fungi, & some bacteria, & protist s </li></ul>
  3. 3. Light Absorption <ul><li>Chloroplasts absorb light from the sun during the light dependent reactions </li></ul><ul><li>Photosynthetic cells may have thousands of chloroplasts </li></ul><ul><li>Chloroplasts are double membrane organelles with the an inner membrane folded into disc-shaped sacs called  thylakoids </li></ul><ul><li>Thylakoids, containing  chlorophyll  and other  accessory pigments , are in stacks called  granum  (grana, plural) </li></ul><ul><li>Grana are connected to each other & surrounded by a gel-like material called  stroma </li></ul><ul><li>Light-capturing pigments in the grana are organized into  photosystems </li></ul>
  4. 4. Leaf Structure <ul><li>Most photosynthesis occurs in the palisade layer. </li></ul><ul><li>Gas exchange of CO 2 and O 2 occurs at openings called stomata surrounded by guard cells on the lower leaf surface. </li></ul>Palisade Spongy
  5. 5. Chloroplast Structure <ul><li>Inner membrane called the thylakoid membrane. </li></ul><ul><li>Thickened regions called thylakoids . A stack of thylakoids is called a granum . (Plural – grana) </li></ul><ul><li>Stroma is a liquid surrounding the thylakoids. </li></ul>
  6. 6. Pigments <ul><li>Chlorophyll A is the most important photosynthetic pigment. </li></ul><ul><li>Other pigments called antenna or accessory pigments are also present in the leaf. </li></ul><ul><ul><li>Chlorophyll B </li></ul></ul><ul><ul><li>Carotenoids (orange / red) </li></ul></ul><ul><ul><li>Xanthophylls (yellow / brown) </li></ul></ul><ul><li>These pigments are embedded in the membranes of the chloroplast in groups called photosystems . </li></ul>
  7. 7. Photosynthesis : The Chemical Process <ul><li>Occurs in two main phases. </li></ul><ul><ul><li>Light reactions </li></ul></ul><ul><ul><li>Dark reactions (aka – the Calvin Cycle) </li></ul></ul><ul><li>Light reactions are the “photo” part of photosynthesis. Light is absorbed by pigments. </li></ul><ul><li>Dark reactions are the “synthesis” part of photosynthesis. Trapped energy from the sun is converted to the chemical energy of sugars. </li></ul>
  8. 8. Calvin Cycle <ul><li>Carbon atoms from CO2 are bonded or &quot;fixed&quot; into organic compounds during a process called  carbon fixation </li></ul><ul><li>The energy stored in ATP and NADPH during the Light Reactions is used in the Calvin cycle </li></ul><ul><li>The Calvin cycle has  3 main steps  occurring within the  stroma  of the Chloroplast </li></ul><ul><li>1.  Carboxylation  - CO2 is covalently linked to a carbon skeleton (RuBP) 2.  Reduction  - carbohydrate is formed at the expense of ATP and NADPH 3.  Regeneration  - the CO2 acceptor RuBP reforms at the expense of ATP </li></ul>
  9. 9. Light Reactions <ul><li>Light-dependent reactions occur on the thylakoid membranes. </li></ul><ul><ul><li>Light and water are required for this process. </li></ul></ul><ul><ul><li>Energy storage molecules are formed. (ATP and NADPH) </li></ul></ul><ul><ul><li>Oxygen gas is made as a waste product. </li></ul></ul>
  10. 10. Dark Reactions <ul><li>Dark reactions (light-independent) occur in the stroma. </li></ul><ul><ul><li>Carbon dioxide is “fixed” into the sugar glucose. </li></ul></ul><ul><ul><li>ATP and NADPH molecules created during the light reactions power the production of this glucose. </li></ul></ul>
  11. 11. Factors Determining the Rate of Photosynthesis <ul><li>Light intensity - As light intensity increases, the rate of photosynthesis initially increases and then levels off to a plateau </li></ul><ul><li>Temperature - Only the dark, not the light reactions are temperature dependent because of the enzymes they use (25 oC to 37oC) </li></ul><ul><li>Length of day </li></ul><ul><li>Increasing the amount of carbon dioxide available improves the photosynthesis rate </li></ul><ul><li>Level of air pollution </li></ul>
  12. 12. Photosynthesis in Overview <ul><li>Process by which plants and other autotrophs store the energy of sunlight into sugars. </li></ul><ul><li>Requires sunlight, water, and carbon dioxide. </li></ul><ul><li>Overall equation: </li></ul><ul><li>6 CO 2 + 6 H 2 0  C 6 H 12 O 6 + 6 O 2 </li></ul><ul><li>Occurs in the leaves of plants in organelles called chloroplasts. </li></ul>

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