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Photosynthesis: An Overview
Some details:
LightReaction
Dark Reaction
Sunlight
Water Oxygen
Carbon Dioxide
Glucose
ATP NADH
Today’s Goal!
To explain how energy is transferred from sunlight to glucose via the light and dark reactions of photosynthesis.
ThylakoidsThylakoids
(Light DEPENDENT)(Light DEPENDENT)
StromaStroma
(Light INDEPENDENT)(Light INDEPENDENT)
CALVINCALVIN
Inner and outer Inner and outer membrane ofmembrane of chloroplastchloroplast
THE CHLOROPOPLASTTHE CHLOROPOPLAST
Light dependent and light Light dependent and light independent reaction locationsindependent reaction locations
Pigments- Important for the absorption of light energy
Three types:
1. Chlorphyll a- absorbs all spectrum of light except for green
2. Chlorophyll b- absorbs most spectrum of light except orange, yellow or red
3. Carotene- absorbs most spectrum of light except for orange
So why are plant leaves green?
Another Question: Why are leaves a different color in the fall? See the next slide for the answer from a celebrity presenter.
1. In the Fall the strength of the sun decreases.
2. Plants will decrease their production of chlorophyll a in order to conserve more sugar for the winter months. (remember that when the body builds something it requires energy)
3. The remaining pigments will reflect different spectrum of light depending on the species.
Thanks David!
Hey! Its David Ortiz…maybe he can explain why the leaves change color in the fall.
Electron CarriersWhat do they do?• Electron carriers take high energy electrons (stored
on H) and bring them to electron transport chains (more on these later)
• The electrons become high energy when exposed to sunlight
Examples:
1. With electronsNADPH or FADH2
2. Without electrons NADP+ or FAD+
e-NADP+
FAD+
e-e-
e-
e-
e-
e-
NADPH
FADH2+
1. Sunlight hits chlorphyll and excites the electrons (woo hoo!)
2. These electrons are transferred to electron carriersReally
excited electrons
Electron carriers
3. These electrons are used to split water molecules (this is why plants produce oxygen)
e-e- e-e-
e- Excited electrons splitting H20 molecule into its base elements
H+H+
O- leaves the plant via stomata
H+’s used to help carry electrons (FAD+ becomes FADH2 when it carries electrons)
4. These Hydrogen ions are also shot across an electron transport chain (against the proton gradient…remember the sledding example)
- - - - - - - - - - - - - - - - - - -
++
+++
++ +
+
H+
The Electron Transport Chain is represented by the dashed line and has one side which is highly positive…shooting the Hydrogen ions against the positive gradient creates energy.
H+ H+ H+ H+ H+ H+ H+
5. This produces enough energy to make a small amount of ATP which will be used in the Calvin Cycle
ATP
ATP
SYNTHASE
ADP + P
Energy from electron transport chain Note the H+ ions returning
through ATP Synthase…Oxygen picks up these ions and forms H20…more on this when we get to cellular respiration
Light-dependent Reaction-Takes Place in Thykaloid
1. Sunlight hits chlorphyll and excites the electrons (woo hoo!)
2. These electrons are transferred to electron carriers
3. These electrons are used to split water molecules (this is why plants produce oxygen)
4. Hydrogen ions are also shot across an electron transport chain (against the gradient…remember the sledding example)
5. This produces enough energy to make a small amount of ATP which will be used in the Calvin Cycle
1. The plant “breaths in” C02 via stomata
Electron micrograph photo of stomata(s)
CO2
CO2 CO2
CO2CO2
CO2
Plant taking in CO2
Lets zoom in
2. The ATP and NADPH produced in the light reaction is used to break apart the CO2 into its base elements
Energy from ATP and NADPH
Carbon Dioxide being split into base elements
O-
O-C
3. With enough C02 and H (remember when the water molecule was split?) a glucose molecule is formed (what was that formula again?)
O-
O-
O-
O-
O-
O-
C
C
CC
C
C
+ +H+
H+
H+
H+
H+
H+ H+
H+
H+
H+
H+
H+
C6H12O6
Aka: Glucose
Oxygen’s from the splitting of H20
Carbon’s from Carbon Dioxide
Hydrogen’s from the splitting of H20
Calvin Cycle-takes place in Stroma
2. The ATP and NADPH produced in the light reaction is used to break apart the CO2 into its base elements
1. The plant “breaths in” C02
3. With enough C02
and H (remember when the water molecule was split?) a glucose molecule is formed (what was that formula again?)