5.1.1 Light-Dependent Reactions

• Thylakoid membranes are arranged into stacks called grana.
• Chlorophyll a absorbs blue-violet and red light most effectively.
• What type of light does chlorophyll b absorb most effectively?

  Blue and yellow-green
• Carotenoids protect chlorophyll from excessive light damage through quenching.
• What are the three main types of pigments involved in light absorption during photosynthesis?

  Chlorophyll a, Chlorophyll b, Carotenoids
• The electron transport chain releases energy to drive ATP synthesis.
• ATP and NADPH store chemical energy for use in the Calvin cycle.
• What is the role of grana in photosynthesis?

  Stacks of thylakoids
• The thylakoid structure provides a large surface area for the light-dependent reactions.
• Chlorophyll a is the primary pigment that directly participates in the light reactions.
• What is the chemical formula of chlorophyll b?

  $C_{55}H_{70}MgN_{4}O_{6}$
• Carotenoids protect chlorophyll from damage by absorbing excess light.
• What type of light is absorbed by pigments in PSII?

  Light energy
• Light is absorbed by pigments such as chlorophyll a
• What happens to electrons after they are excited by light energy in PSII?

  They are transferred
• Electrons in PSII are passed through a series of electron carriers in the thylakoid membrane.
• The energy from light is used to split water into oxygen, protons, and electrons
• What three products are formed during water splitting in PSII?

  Oxygen, protons, electrons
• The accumulation of protons in the thylakoid lumen creates a proton gradient that drives ATP synthesis.
• The proton gradient in the thylakoid lumen drives the synthesis of ATP
• Steps involved in Photosystem II (PSII)

  1️⃣ Light Absorption

  2️⃣ Excitation of Electrons

  3️⃣ Electron Transfer

  4️⃣ Water Splitting

  5️⃣ ATP Synthesis
• Where does electron transfer occur in PSII?

  Thylakoid membrane
• Water splitting in PSII produces oxygen, protons, and electrons.
• What is the primary outcome of water splitting in PSII?

  Oxygen production
• The proton gradient in the thylakoid lumen is used to synthesize ATP
• Which molecule accumulates in the thylakoid lumen during ATP synthesis?

  Protons
• Electron transfer in PSII involves energized electrons being passed through a series of carriers in the thylakoid membrane.
• Match the process in PSII with its outcome:

  Light Absorption ↔️ Excitation of electrons

  Water Splitting ↔️ Oxygen, protons, and electrons produced

  Electron Transfer ↔️ Energized electrons passed through carriers

  ATP Synthesis ↔️ ATP generated via proton gradient
• The energy from light is used to split water into oxygen, protons, and electrons
• The proton gradient in the thylakoid lumen drives ATP synthesis during the light-dependent reactions.
• Steps of the light-dependent reactions as described in the table:

  1️⃣ Light Absorption: Excitation of electrons

  2️⃣ Electron Transfer: Energized electrons passed through carriers

  3️⃣ Water Splitting: Oxygen, protons, and electrons produced

  4️⃣ ATP Synthesis: ATP generated via proton gradient
• What are the primary pigments that absorb light in Photosystem II (PSII)?

  Chlorophyll a
• The electrons released during water splitting in PSII are used to generate ATP and NADPH.
• Light is absorbed by pigments in PSII, such as chlorophyll a and other accessory
• Steps of PSII as described in the table:

  1️⃣ Light Absorption: Excitation of electrons

  2️⃣ Electron Transfer: Energized electrons passed through carriers

  3️⃣ Water Splitting: Oxygen, protons, and electrons produced

  4️⃣ ATP Synthesis: ATP generated via proton gradient
• Which molecule is reduced to NADPH in Photosystem I (PSI)?

  NADP+
• Energized electrons in PSI are passed to ferredoxin before reducing NADP+.
• PSI complements PSII by regenerating NADPH needed for carbon fixation
• Steps of PSI as described in the table:

  1️⃣ Light Absorption: Excitation of electrons

  2️⃣ Electron Transfer: Energized electrons passed through carriers

  3️⃣ NADPH Formation: Electrons reduce NADP+
• Where do the light-dependent reactions occur in chloroplasts?

  Thylakoid membranes