Photosynthesis

• Where is the site of photosynthesis in plants?

  Chloroplasts in the leaf
• How is the leaf adapted for photosynthesis?

  • Large surface area to absorb sunlight
  • Thin structure for short gas diffusion pathway
  • Waxy cuticle and transparent upper epidermis to let light through
  • Stomata for gas exchange
  • Air spaces in lower mesophyll for rapid diffusion
  • Xylem and phloem for water transport and sugar distribution
• What is the overall equation for photosynthesis?

  6CO2 + 6H2O —> C6H12O6 + 6O2
• What are the structures found in the chloroplast?


  • Lamellae
  • Outer membrane
  • Inner membrane
  • Thylakoids
  • Granum
  • Stroma
• What is oxidation in the context of photosynthesis?

  Gain of oxygen, loss of electrons, or loss of hydrogen
• What is reduction in the context of photosynthesis?


  Loss of oxygen, gain of electrons, or gain of hydrogen
• Where are photosynthetic pigments located?

  Thylakoid membranes
• What is the most common photopigment in plants?

  Chlorophyll
• Where does the light-dependent reaction of photosynthesis take place?

  Thylakoid membrane
• What happens during the process of photoionisation?

  1. Photosystem 2 absorbs light energy from the sun.
  2. Electrons within the chlorophyll molecule are excited.
  3. Electrons are released from the chlorophyll molecule.
  4. The chlorophyll molecule becomes ionised.
  5. Electrons are taken up by an electron carrier.
• What happens to the chlorophyll molecule after it loses a pair of electrons?

  The chlorophyll molecule is oxidised.
• What happens to the electron carrier after it gains electrons?

  The electron carrier is reduced.
• What is photolysis?

  Light energy splits water into protons, electrons, and oxygen.
• Why does photolysis occur?


  To replace electrons lost from photosystem 2 and to produce protons for NADPH synthesis.
• What happens to the electrons after photoionisation?

  They pass along a number of electron carriers in a series of redox reactions.
• What does the passage of electrons through an electron transfer chain release?


  Energy
• What is the energy released from electrons passing down an electron transfer chain used for?

  To pump H+ ions from the stroma into the thylakoid.
• What is the process of chemiosmosis?

  • A gradient of protons is formed across the thylakoid membrane.
  • Protons move down their electrochemical gradient into the stroma through ATP Synthase (facilitated diffusion).
• What is photophosphorylation?

  The overall process of using light energy and the electron transport chain to phosphorylate ADP to ATP.
• What happens after chemiosmosis?

  This process provides the energy needed to synthesize ATP by adding inorganic phosphate to ADP.
• What happens as protons pass through ATP synthase channels?

  They cause changes to the structure of the enzyme, catalyzing the combination of ADP with Pi to form ATP.
• What happens when light energy hits photosystem 1?

  Photoionisation occurs and electrons become excited.
• What happens to the electrons released from photosystem 1?

  They combine with a proton and NADP to form reduced NADP (NADPH).
• What are the electrons released from the photolysis of water used for?

  They replace those lost from photosystem 2.
• What is a waste product of the photolysis of water?

  Oxygen
• Where does the light-independent reaction take place?

  In the stroma of the chloroplast.
• What are the reactants in the light-independent reaction and where do they come from?

  • Reactants: CO2, NADPH, ATP
  • CO2 diffuses from the atmosphere into the leaf.
  • NADPH and ATP come from the light-dependent reaction.
• What are the products of the light-independent reaction?

  • Useful organic substances (e.g., glucose)
  • ADP + Pi and NADP (these return to the light-dependent reaction)
• What is the first step of the Calvin cycle?

  Carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate-3-phosphate (G-3-P), catalysed by rubisco.
• What is the second step of the Calvin cycle?

  • ATP is hydrolysed to ADP + Pi.
  • NADPH is oxidised to NADP.
  • They are used to reduce GP to triose phosphate (TP).
  • Some TP is converted into useful organic substances.
• What happens to the rest of the TP that is not converted to useful organic substances?

  It is used to regenerate RuBP using the rest of the ATP which is hydrolysed to ADP + Pi.
• How many times must the Calvin cycle occur to form one molecule of glucose?

  6 times