5.6.1 Light-dependent reactions

• The energy from absorbed light excites electrons, which are then passed through an electron transport chain to generate a proton gradient.
• Arrange the key stages of the light-dependent reactions in the correct order.

  1️⃣ Light absorption

  2️⃣ Electron transport chain

  3️⃣ ATP synthesis

  4️⃣ NADPH formation
• What two processes is Photosystem II (PSII) responsible for in the light-dependent reactions?

  Light absorption and water splitting
• What gradient do the protons from water splitting contribute to across the thylakoid membrane?

  Proton gradient
• The light-dependent reactions convert sunlight into chemical energy in the form of ATP and NADPH.
• Photosystem II (PSII) is located in the thylakoid membranes within chloroplasts.


  True
• Accessory pigments absorb specific wavelengths of light and transfer the energy to a chlorophyll molecule in the reaction center
• PSII uses a protein complex to split water molecules into protons, electrons, and oxygen.


  True
• Steps in the electron transport chain during photosynthesis

  1️⃣ PSII absorbs sunlight and splits water

  2️⃣ Electrons are carried to PQ

  3️⃣ Electrons move through the cytochrome complex

  4️⃣ PC carries electrons to PSI

  5️⃣ PSI absorbs sunlight and reduces NADP+
• The electron transport chain creates a proton gradient that drives ATP synthesis.


  True
• What is the primary function of PSI in the light-dependent reactions?

  Reduces NADP+ to NADPH
• Steps in the NADPH formation process by PSI

  1️⃣ PSI absorbs light

  2️⃣ Electrons are transferred from the electron transport chain

  3️⃣ NADP+ is reduced to NADPH
• What are the two main products of the light-dependent reactions?

  ATP and NADPH
• Stages of the light-dependent reactions

  1️⃣ Light absorption

  2️⃣ Electron transport chain

  3️⃣ ATP synthesis

  4️⃣ NADPH formation
• PSII splits water molecules into protons, electrons, and oxygen
• What are the light-dependent reactions the first stage of in photosynthesis?

  Energy conversion
• What gradient is created by the electron transport chain in the light-dependent reactions?

  Proton gradient
• The light-dependent reactions take place in the thylakoid membranes within chloroplasts.


  True
• Water splitting in PSII produces protons, electrons, and oxygen as a byproduct.
• Oxygen is released during water splitting in PSII.


  True
• What enzyme is driven by the proton gradient to produce ATP in the light-dependent reactions?

  ATP synthase
• What is the source of electrons for PSII in the light-dependent reactions?

  Water
• What happens to electrons in chlorophyll when light energy is absorbed?

  They become excited
• The balanced equation for water splitting in PSII is 2H2O → 4H+ + 4e- + O2
• During electron transport, the cytochrome complex pumps protons from the stroma into the thylakoid lumen
• Match the component with its function in the electron transport chain:

  PSII ↔️ Splits water

  PQ ↔️ Carries electrons from PSII

  Cytochrome Complex ↔️ Pumps protons

  PSI ↔️ Reduces NADP+
• PSI absorbs light to excite electrons in its chlorophyll.


  True
• NADPH, along with ATP, provides the necessary energy for the light-independent reactions in the Calvin
• The electron transport chain generates a proton gradient across the thylakoid membrane.


  True
• Where is PSII located within the chloroplast?

  Thylakoid membranes
• Electrons from water splitting replenish those lost by chlorophyll in PSII.


  True
• Chlorophyll and accessory pigments within PSII capture light energy
• What protein complex does PSII use to split water molecules?

  Water-splitting complex
• Oxygen produced during water splitting in PSII is released into the atmosphere.


  True
• The source of electrons for PSI is Photosystem II
• Steps of electron flow in the electron transport chain during photosynthesis

  1️⃣ PSII absorbs sunlight and splits water

  2️⃣ Electrons move to Plastoquinone (PQ)

  3️⃣ Electrons transfer to the Cytochrome Complex

  4️⃣ Electrons are carried to Plastocyanin (PC)

  5️⃣ PSI absorbs sunlight and reduces NADP+
• The proton gradient created by the electron transport chain is used to generate ATP
• What type of energy does NADPH provide in the Calvin cycle?

  Reducing power
• What does the F0 subunit of ATP synthase form within the membrane?

  Proton channel
• Match the feature with its location in ATP synthase:

  Proton gradient source in chloroplasts ↔️ Light-dependent reactions

  Proton gradient source in mitochondria ↔️ Electron transport chain

  ATP usage in chloroplasts ↔️ Calvin cycle