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Topic 5: On the Wild Side
5.1 Photosynthesis
5.1.1 Light-Dependent Reactions
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What are the three products of the light-dependent reactions?
Oxygen, ATP, NADPH
The light-dependent reactions occur in the thylakoid membranes of
chloroplasts
.
Thylakoids are stacked into structures called
grana
What type of light does chlorophyll a absorb most effectively?
Blue-violet and red
Chlorophyll b broadens the light spectrum by absorbing blue and yellow-
green
light.
What is the role of carotenoids in photosynthesis?
Light absorption and photoprotection
Main steps of the light-dependent reactions
1️⃣ Light absorption by pigments
2️⃣ Electron transfer through ETC
3️⃣ ATP and NADPH production
The light-dependent reactions take place in the thylakoid membranes of
chloroplasts
.
The thylakoid structure provides a large surface area for light absorption and electron
transfer
.
Match the pigment with its role in photosynthesis:
Chlorophyll a ↔️ Primary photosynthetic pigment
Chlorophyll b ↔️ Enhances light absorption
Carotenoids ↔️ Light absorption and photoprotection
What is the first step in Photosystem II (PSII)?
Light absorption
In PSII, energized electrons are passed through a series of electron
carriers
in the thylakoid membrane.
Steps involved in Photosystem II (PSII) during photosynthesis
1️⃣ Light Absorption by pigments
2️⃣ Excitation of Electrons
3️⃣ Electron Transfer through carriers
4️⃣ Water Splitting
5️⃣ ATP Synthesis
What is the primary pigment in Photosystem II that absorbs light?
Chlorophyll a
The absorbed light energy excites electrons, which are then transferred to the reaction
center
Where are the electron carriers located in Photosystem II?
Thylakoid membrane
Water splitting in Photosystem II releases
oxygen
, protons, and electrons.
The accumulation of protons in the thylakoid lumen creates a proton
gradient
What is the overall equation for the light-dependent reactions initiated by PSII?
2H_{2}O + light \rightarrow O_{2} + 4H^{ + } + 4e^{ - }</latex>
Match the products of the light-dependent reactions with their role:
Oxygen ↔️ Released into the atmosphere
Protons ↔️ Create a gradient for ATP synthesis
Electrons ↔️ Used to generate ATP and NADPH
What is the role of Photosystem II (PSII) in the light-dependent reactions of photosynthesis?
Crucial component
Steps involved in Photosystem II (PSII)
1️⃣ Light Absorption
2️⃣ Excitation of Electrons
3️⃣ Electron Transfer
4️⃣ Water Splitting
5️⃣ ATP Synthesis
Water splitting in PSII releases oxygen, protons, and
electrons
What is the overall equation for the light-dependent reactions initiated by PSII?
2H_{2}O + light \rightarrow O_{2} + 4H^{ + } + 4e^{ - }</latex>
Photosystem I (PSI) complements PSII by regenerating
NADPH
for carbon fixation
In PSI, energized electrons are passed to ferredoxin, then to
NADP+
What is the overall chemical equation for NADPH formation in PSI?
2
N
A
D
P
+
+
2NADP^{ + } +
2
N
A
D
P
+
+
4
H
+
+
4H^{ + } +
4
H
+
+
4
e
−
→
2
N
A
D
P
H
+
4e^{ - } \rightarrow 2NADPH +
4
e
−
→
2
N
A
D
P
H
+
2
H
+
2H^{ + }
2
H
+
The light-dependent reactions produce oxygen, ATP, and
NADPH
Light-dependent reactions use light energy to convert water into oxygen, ATP, and
NADPH
Where do the light-dependent reactions occur in the chloroplast?
Thylakoid membranes
Thylakoids are stacked into structures called grana, which increase the surface area for
light-dependent reactions
The thylakoid membranes are the site of the light-dependent
reactions
What are grana in the chloroplast composed of?
Stacks of thylakoids
Match the photosynthetic pigment with its role:
Chlorophyll a ↔️ Primary photosynthetic pigment
Chlorophyll b ↔️ Enhances light absorption
Carotenoids ↔️ Light absorption, photoprotection
Chlorophyll a absorbs blue-violet and
red
light most effectively
Chlorophyll b broadens the spectrum of light plants can
utilize
What type of light does chlorophyll a absorb most effectively?
Blue-violet and red
Chlorophyll a is the primary pigment directly participating in
light reactions
.
Chlorophyll b broadens the spectrum of light that plants can
utilize
What is the role of carotenoids in photosynthesis?
Protect chlorophyll from light damage
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