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I. PhotosynthesisI. Photosynthesis
The process of converting light energy into chemical bond energy in the form of glucose
Supplies energy and oxygen to virtually all living things
II. ChloroplastsII. Chloroplasts
The site of photosynthesis Chloroplasts contain chlorophyll absorb
light use energy to drive photosynthesis Three functional parts inside the
chloroplast
1. Intermembrane Space1. Intermembrane Space
Chloroplasts is a double membrane Intermembrane space separates the two
membranes
2. Thylakoid2. Thylakoid Flattened membrane sacs inside
chloroplast Chlorophyll is found here Light reactions take place here Grana stacks of thylakoids
3. Stroma3. Stroma
Fluid filled space that surrounds grana Reactions that use chemical energy to
convert carbon dioxide to sugar occur here These are called
dark-reactions
III. Light ReactionsIII. Light Reactions Occur in the thylakoid membranes of
chloroplasts Light energy excites a pair of electrons Electrons passed to different “carriers” – they
lose a bit of energy at each step Generate ATP (photophosphorylation) and
NADPH as they give off energy Give off oxygen as a by-product from splitting of
water
IV. Noncyclic Electron FlowIV. Noncyclic Electron Flow
Involve PS I and PS II Occurs in thylakoids Passes electrons continuously from water to
NADP+ Produces ATP Produces NADPH Produces oxygen
V. Cyclic Electron FlowV. Cyclic Electron Flow
Involves only PS I Makes ATP Does not produce NADPH or oxygen
Bottom Line:Bottom Line:
Light reactions take energy from light and hold it for later use Held in ATP and NADPH
VI. Calvin Cycle – the Dark ReactionsVI. Calvin Cycle – the Dark Reactions Carbon-fixation reactions that assimilate 6
Carbons into a carbohydrate Occurs in the stroma ATP and NADPH produced by light reactions are
used in the Calvin cycle to turn carbon dioxide to sugar
NADPH provides the reducing power ATP provides the chemical energy
More Calvin Cycle…More Calvin Cycle…
End product of the Calvin Cycle is a glucose molecule
Uses 18 ATP molecules and 12 NADPH molecules
3 CO2 + 6 NADPH + 5 H2O + 9 ATP → C3H5O3-PO32- + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi
Bottom Line:Bottom Line:
Water donates electrons Light provides energy CO2 provides the
carbons for sugar
Photosynthesis As a ProcessPhotosynthesis As a Process
Water is split, oxygen is released, sugar gets made from CO2
…mmmmm…. sugar
Energy for PhotosynthesisEnergy for Photosynthesis OIL RIG
Oxidation is loss of electrons, reduction is gain of electrons
Photosynthesis is an endergonic process: energy is required to reduce carbon dioxide to sugar
Light provides energy of electrons as they are moved from water to sugar
Energy for Photosynthesis (cont’d)Energy for Photosynthesis (cont’d)
Water is split, electrons are transferred from the water to carbon dioxide (via NADPH), reducing it to sugar
There are two separate parts to photosynthesis Light reactions (the “Photo”) Calvin Cycle (dark reactions) – (the “synthesis”)
IV. Respiration – Returning the EnergyIV. Respiration – Returning the Energy We digest sugar, and energy is released in the
form of ATP. Sugar gets oxidized (loses electrons) and the
energy released makes ATP This happens in all cells of plants, animals, and
bacteria The byproduct is CO2, which is then used to
make new sugar through photosynthesis
PHEW! Take a breather!PHEW! Take a breather!
On with Photosynthesis!!!
III. Photosynthesis As a ProcessIII. Photosynthesis As a Process
Light energy absorbed; CO2 absorbed; O2 released from water; sugar produced
Plants split the water to release Hydrogen to make NADPH
Plants absorb light to energize electrons in the thylakoid membrane
Sugars provide a more useful storage form for the energy in the electrons released from water
IX. The Good Stuff…IX. The Good Stuff… Light reactions take
energy in as light and store it as ATP and NADPH
Dark reactions take the energy stored in ATP and NADPH to make sugar molecules
*****We take glucose in and convert the energy in glucose back to ATP so our bodies can use it*****
X. Three Types of PlantsX. Three Types of Plants C3 plants: These include rice, wheat, beans Most plants are C3 which means 3-
phosphoglycerate is produced
C4 plants: crab grass and sugarcane, plants in hot regions They make a 4 carbon compound prior to the Calvin
Cycle An adaptation for plants that grow in hot regions, when
stomata are closed
X. Three Types of Plants (cont’d)X. Three Types of Plants (cont’d) CAM plants: (crassulacean acid metabolism) Occurs in many desert dwelling plants such as
cacti Open stomata at night instead of during the day.
Carbon gets fixed at night. The only difference in these plants is the time of
carbon fixation; they still all use the Calvin Cycle to produce sugar from CO2