Energy in Living Systems
• CH 9 pg 197 - 213
Organisms classified on how they obtain energy
• Autotrophs
– Make their own food from organic molecules
– Most convert light energy into chemical energy
• Carbon Dioxide (CO
2
) and water (H
2
O) to organic compound
• Oxygen (O
2
) released
• Heterotrophs
– Cannot make their own food inorganic compounds
– Eat autotrophs or other heterotrophs
• Photosynthesis
Harvesting Light Energy
• Photosynthetic organisms have chloroplasts
– Chloroplasts are the organelles that convert light energy into chemical energy.
• Contains flat, disc-like sacs called thylakoids.
• this is the first stage of photosynthesis.
• Thylakoids
• Light Absorption in Chloroplast
• Sunlight composed of ROY G BIV, different colors. (Lgth = Amt of Engy)
• Color observed when light strikes an object, waves are reflected, transmitted, or absorbed
• Colors react depending on the pigment present
Harvesting Light Energy, continued
• Chlorophyll (a and b)
– Absorbs blue and red light and reflects green and yellow light
• Carotenoids
– help plants absorb additional light energy
– absorb blue and green light, reflect red, orange and yellow(fall colors)

Two Electron Transport Chains
• First reaction in photosynthesis is the light reaction takes place in the chlorophyll
– Light hits a thylakoid
– Energy is absorbed by the pigment molecules and are directed to a special chlorophyll molecule that acts as a reaction center
– Electrons are excited and move to other molecules and the electron transport chain.
• One ETC makes ATP and Second makes NADPH
Producing ATP
Step 1:
• An enzyme splits water molecules .
• H + ions are used by the chlorophyll
• Oxygen gas is released into the atmosphere
Step 2:
• Carrier Proteins (ATP Synthase) in the membrane pump H + ions into the thylakoid,
Step 3:
• Energy diffusion of H+ ions through ATP synthase is used to make ATP
• 2 nd Electron Transport Chain
Step 4: Producing NADPH
• Renergizing, Light excites electrons that are passed on to the second chain.
Step 5: Making NADPH
• Excited electrons combine with H+ ions and NADP+ to form NADPH.
• NADPH is used to store energy in organic molecules. (used later in dark reaction)
• Electron Transport Chains of Photosynthesis
Producing Sugar
• The first two stages of photosynthesis depend directly on light to make ATP and NADPH.
• In the final stage of photosynthesis, ATP and NADPH are used to produce energy-storing sugar molecules from the carbon in carbon dioxide.
• The use of carbon dioxide to make organic compounds is called carbon dioxide fixation, or carbon fixation. (Light
Independent, Dark Reaction, or Calvin Cycle)

Calvin Cycle
• The use of carbon dioxide to make organic compounds is called carbon dioxide fixation, or carbon fixation. (Light
Independent, Dark Reaction, or Calvin Cycle)
• Carbon Fixation, an enzyme adds CO
2
to a five carbon compound. This occurs 3 times to make 3 – six carbon molecules
Calvin Cycle
• Takes place outside of thylakoid
• CO
2
is taken in
• NADPH drops off the hydrogen atoms and energy (ATP) and returns to the thylakoid
• CO
2
and Hydrogen and ATP combine to make glucose
Factors that Affect Photosynthesis
• Light intensity
• Carbon dioxide concentration
• Temperature