How do organisms obtain energy?
   • Autotrophs
     –Able to produce their own food
      • Ex. Plants use sunlight to produce energy
      • Photosynthesis
   • Heterotrophs
     –Unable to produce their own food, rely on 
      other organisms as a source of energy
      • Ex. Animals need to eat to survive
      • Cellular Respiration
   Organisms rely on PHOTOSYNTHESIS and 
     CELLULAR RESPIRATION for their energy needs
                                                    Heat
     Sunlight
                                        Cellular
                 Photosynthesis        respiration
                                                  Visual Summary 6.1
                    Photosynthesis!
 • What happens during photosynthesis?
     –Plants (autotrophs) use energy from sunlight to 
       convert water and carbon dioxide into 
       carbohydrates (energy) and oxygen
        • 6CO  + 6H O (light) →  C H O  + 6O
              2      2          6  12 6     2
 Reactants?
    Carbon dioxide (CO ) and Water (H O)
                           2                 2
 Products?
    Glucose—Sugar (C H O ) and Oxygen (O )
                           6 12  6                    2
        Photosynthesis: Light and Pigment
    •   In addition to water and carbon 
        dioxide, photosynthesis needs 
        light and chlorophyll (a molecule 
        in chloroplasts)
    •   Light is converted into chemical 
        energy
    •   Occurs in chloroplasts
    •   Chlorophyll absorbs the light (it 
        makes plants green!)
         The Two Parts of Photosynthesis
      •  Light-dependent 
         reactions  
          – Need light to happen
          – Occurs in Chloroplast
          – Produces Oxygen
      •  Light-independent 
         reactions (Calvin Cycle)
          – Does not need light
          – Use energy molecules 
             (NADPH) to produce 
             sugars for the plant