5.1.1 Light-Dependent Reactions

• 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?

  $2NADP^{ + } +$$4H^{ + } +$$4e^{ - } \rightarrow 2NADPH +$$2H^{ + }$
• 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