PHOTOSYNTHESIS by fQ55scW

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									PHOTOSYNTHESIS
       PHOTOSYNTHESIS
 Photosynthesis is ability of a plant to turn
  sunlight, air, and water into sugar
  (energy).
 The overall reaction is:
              light
           chlorophyll
  CO2 +                 + O2
        H2O -------> CH2O
 Photosynthesis is vital to life for two
  reasons
–1. The oxygen in the air comes from
   photosynthesis. The plants continue to
   replenish the oxygen in the air.
–2. All of our food comes directly or
    indirectly from photosynthesis.
Parts of a leaf
 Stomata
 palisade layer
 spongy layer
 veins
 chloroplast
     thylakoids
     grana
     stroma
                   Light
 Photosynthesis   uses visible light.
  – Only visible light with intermediate
    wavelengths has enough energy to cause
    chemical change without destroying
    biological molecules.
 What  are the colors of the visible
  spectrum?
 Why does a leaf look green?
Light is captured by
pigments. The main
photosynthetic pigment is
chlorophyll. There is
chlorophyll a, b and c.
Chlorophyll a is the major
photosynthetic pigment and
is found in all
photosynthetic plants,
protist, and cyanobacteria.
Carotenoids are accessory pigments
found in all green plants. They absorb
blue and green wavelengths and give a
plant a yellow or orange color. In the fall
when chlorophyll breaks down, it is the
accessory pigments which give colors of
fall. The red color of some autumn leaves
is due to the anthocyanin pigments.
These are not photosynthetic.
     Stages of Photosynthesis

    LIGHT REACTIONS          DARK REACTIONS


     Light absorption         Carbon Fixation


    Electron transport


    Oxygen production


Chemiosmotic ATP synthesis
 The Energy-Capturing Reactions
 Light   absorption
  – Chlorophyll a and b are antennae pigments
 Electron   transport
  – Electrons lost by chlorophyll a end up at
    NADP
  – Produce oxygen
 Chemiosmotic       ATP synthesis
  – Powered by H ion reservoir
        The Dark Reactions
 The  dark reactions take place outside
  the thylakoid membrane.
 Carbon fixation - The carbon dioxide is
  incorporated into an organic molecule
  (1C + 5C = 6C). This 6 carbon structure
  is unstable and immediately splits into
  2, 3 carbon molecules. These molecules
  go through a series of reactions known
  as the CALVIN CYCLE.
What controls photosynthesis?
  Intensityof light
  Scarcity of water
                Ecological Aspects
   C4 PLANTS - Use more ATP but at high
    temperatures they can photosynthesize
    faster -allowing plants to grow and
    reproduce faster. These include many
    weeds and important crops such as corn.


               A special variation of C4 plants are the
                CAM plants. These are mostly desert
                plants. These plants keep the stomata
                closed during the day and open at
                night. They must conserve water!
                Vocabulary
 Glossary     of terms
  – blade
  – stipules
  – petiole
  – vein
  – midrib
Vocabulary        NADP+
                  NADPH
                  photon
carotenoids       photosystem
chlorophyll       photosystem I
electromagnetic   photosystem II
    spectrum      pigment
granum            stroma
                  thylakoid

								
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