Light-Dependent Reactions 11/13/15 & 11/16/15
Objective: Be able to explain the processes that occur in the Light-Dependent Reaction of photosynthesis.
Vocabulary: Photosystem I, Photosystem II, NADP, Electron Transport Chain, Photon, ATP Synthase
Group Discussion
1. Beyond water and sunlight, what else is necessary for photosynthesis to occur? Why?
*Hint - Photosynthesis is Cellular Respiration in Reverse
2. What would most likely decrease the rate of photosynthesis? Why?
3. What organelle is most important in the process of photosynthesis? Why?
Video: https://www.youtube.com/watch?v=_hUxKPSNTl0
Label the image as you watch the video
Photosystem II
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Location: in the thylakoid membrane
o Thylakoids contain photosystems that contain chlorophyll
Process of Light Dependent Reaction
Purpose of Photosystem II is to energize the electrons by bouncing multiple times and then bouncing out to the
ETC to make ATP.
Light electrons shine down and hit chlorophyll in Photosystem II found on the thylakoid membrane.
The Light electrons then bounce multiple times on the Chlorophyll trampolines till it finally hits the Reaction
Center of the photosystem II on the Thylakoid membrane.
From the reaction center it bounces out of Photosystem II and on the ETC.
Electron pass from 1 electron acceptor to the next moving across the membrane Remember from before that
they lose energy as they bounce.
Remember that this process is also throwing H ions back over to maintain a gradient.
o As the H ions flow through the ATP Synthase, an ADP and Phosphate combine to form ATP in
Photosystem II.
At the same time, Water is being split into H and O(2)
The Oxygen leaves the cell as waste products. We can now BREATHE!! Love that Mutual relationship this is a
definite win win situation.
Photosystem I
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YES II comes before I
Purpose is to create NADPH
o NADPH is an electron carrier
Location: Thylakoid Membrane.
The electron leaves the PS2 ETC and jumps over to the Chlorophyll in PS1.
The exact same thing happens that happened in PS2.
The electrons get reenergized and bounce around until it hits the reaction center.
Get kicked out at the reaction center and goes to the ETC of PS1
o While going through the ETC H is added to NADP+ making NADPH
 The NADPH is going to provide energy for the light-independent reaction.
Part I
Together draw a diagram showing the path an electron takes through Photosystem II and Photosystem I (make sure to
include all products that are made, and the splitting of water.)
Part II
Divide and conquer. One of you teach the path of Photosystem II and its products, and the other will teach the path of
Photosystem I and its products.
3-2-1
3 things you have learned
2 things you want to know more about
1 question you have
Group Discussion
Okay what did you learn?
what are some of your questions?
Check for understanding
1. Where do the light-dependent reactions take place?
a.
thylakoid
b.
stroma
c.
thylakoid membrane
d.
grana
2. Which photosystem will the electron(s) reach first?
a.
photosystem II
b.
photosystem I
c.
Electron Transport Chain
d.
Reaction Center
3. What do the light-dependent reactions require to begin?
a.
water and sunlight
b.
CO2 and glucose
c.
sunlight and oxygen
d.
water and CO2
4. What are the trampoline like molecules electrons are
bouncing around on when they first enter the
chloroplast?
a.
photosystem I
b.
chlorophyll
c.
electron transport chain
d.
NADPH
5. After the electron hits the reaction center, it bounces
out of photosystem II and into
a.
b.
c.
d.
the electron transport chain of
photosystem I
6. NADPH is made
a.
b.
c.
ATP
in the electron transport chain of
photosystem II
in photosystem I
d.
in the electron transport chain of
photosystem I
7. ATP is made using
a.
the hydrogen gradient between the
stroma and thylakoid space
b.
hydrogens moving through the ATP
Synthase
c.
the electron transport chain of
photosystem II
d.
ADP and a phosphate coming
together
e.
all of the above
8. The reaction center
a.
b.
c.
absorbs chlorophyll
kicks the electron to the electron
transport chain
absorbs the electron
d.
sends the electron to the stroma
9. When water splits
a.
hydrogens move to the thylakoid
space or stroma and oxygen leaves the
cell
b.
oxygen moves to the thylakoid
space or stroma and hydrogen leaves
the cell
c.
it eventually comes back together
and leaves the cell as water again
d.
oxygen and hydrogen both enter
the stroma or thylakoid space
photosystem I
the electron transport chain of
photosystem II
in photosystem II