Light dependent reaction

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

  To convert light energy into chemical energy in the form of ATP and NADPH
• What are the main steps involved in the cyclic light-dependent reaction?

  1. Light energy absorbed by chlorophyll in PS I
  2. Excitation of an electron in PS I
  3. Electron moves down the electron transport chain (ETC)
  4. Energy released is used to join ADP + P to form ATP
  5. NADP is reduced to form NADPH
  6. Photolysis of water produces protons, electrons, and oxygen
• What is the role of PS I in the cyclic light-dependent reaction?

  PS I absorbs light energy and excites electrons
• How is ATP produced in the cyclic light-dependent reaction?

  By the process of chemiosmosis using the energy released from electrons moving down the ETC
• What is produced when NADP is reduced in the light-dependent reactions?

  Reduced NADP (NADPH)
• What is the role of PS II in the non-cyclic light-dependent reaction?

  PS II absorbs light energy and excites electrons
• What is the significance of the proton gradient created during the non-cyclic light-dependent reaction?

  It is used to synthesize ATP through chemiosmosis
• How do the cyclic and non-cyclic light-dependent reactions differ in terms of electron flow?

  Cyclic reactions recycle electrons back to PS I, while non-cyclic reactions transfer electrons to NADP
• What is produced as a byproduct of photolysis in the light-dependent reactions?

  Oxygen
• What is the role of the electron transport chain (ETC) in the light-dependent reactions?

  To transfer excited electrons and release energy for ATP synthesis
• What is the final electron acceptor in the light-dependent reactions?

  NADP
• If light energy is not available, what would happen to the light-dependent reactions?

  The reactions would not occur, and ATP and NADPH would not be produced
• What is the relationship between the light-dependent reactions and the Calvin cycle?

  The light-dependent reactions produce ATP and NADPH, which are used in the Calvin cycle to synthesize glucose
• What is the process of photolysis in photosynthesis?

  It is the splitting of water molecules to release protons and oxygen.
• What role do protons play in ATP production during photosynthesis?

  Protons create a gradient that drives ATP synthesis through chemiosmosis.
• How does energy from light affect electrons in photosystem II (PSII)?

  Energy from light excites electrons in PSII, allowing them to be transferred to the electron transport chain.
• What is the function of photosystem I (PSI) in photosynthesis?

  PSI is responsible for the final electron transfer and the reduction of NADP+ to NADPH.
• What happens to the electrons that are excited in PSI?

  They are transferred to NADP+ to form NADPH.
• How does the proton gradient contribute to ATP synthesis in chloroplasts?

  The proton gradient drives protons back through ATP synthase, producing ATP from ADP and inorganic phosphate.
• What is the significance of the electron transport chain in photosynthesis?

  It facilitates the transfer of electrons and the generation of a proton gradient for ATP synthesis.
• What are the main steps involved in the light-dependent reactions of photosynthesis?

  1. Photolysis of water to release protons and oxygen.
  2. Excitation of electrons in PSII by light energy.
  3. Transfer of excited electrons through the electron transport chain.
  4. Creation of a proton gradient.
  5. ATP synthesis via ATP synthase.
  6. Excitation of electrons in PSI and reduction of NADP+ to NADPH.
• What is the end product of the light-dependent reactions of photosynthesis?

  The end products are ATP and NADPH.
• What is the role of chlorophyll in photosynthesis?

  Chlorophyll absorbs light energy, which is essential for the excitation of electrons.
• How do the processes in PSII and PSI differ in terms of electron flow?

  PSII generates electrons from water, while PSI receives electrons from the electron transport chain.
• what occurs in non-cyclic?

  1. photolysis of water
  2. light energy excites electrons in PS II
  3. electrons leave PS II replaced by those from water
  4. electrons pass down transport chain - energy used to pump a proton from stoma to thylakoid space
  5. light energy excites electrons in PS I
  6. electrons leave PS I replaced by those from PS II
  7. electrons from PS I used to reduce NADP
  8. proton gradient - photolysis produces H+, pumped into thylakoid, H+ used to reduce
  9. proton motive force used to produce ATP by chemiosmosis
• why does a lack of iron in the soil reduce growth in plants?

  • iron ions needed for electron carriers
  • fewer electron carriers, fewer electrons transported so less ATP and reduced NADP are produced
• how do guard cells use ATP to control the opening and closing of stomata?

  1. potassium ions actively pumped into guard cells
  2. high K+ concentration lowers the water potential inside guard cells
  3. water enters guard cells by osmosis
  4. guard cells become turgid
  5. thicker, less flexible cell wall inside and thinner more flexible cell wall on outside - swells unevenly so stomata open