Key Questions

• What two molecules are the raw materials for photosynthesis?


  Carbon dioxide and water
• What two molecules are the products of photosynthesis?


  Glucose and oxygen.
• What adaptations does a plant have for photosynthesis?


  -Leaf cells contain chlorplasts

  -Large number of leaves with flatted structure to maximise light absorpion by chloroplasts

  =Stomata on underside for gas exchange in order to gain carbon dioxide
• What is a stack of thylakoids called?


  Granum (plural = grana)
• What is the fluid in chloroplasts called?


  Stroma.
• Where do the light dependent and light independent reactions occur?

  Light dependent: thylakoid membrane Light independent: stroma of the chloroplast
• What is photoionisation?


  When light causes electrons to become excited and leave chlorphyll.
• What is the role of NADP?


  NADP is a molecule that carries electrons and hydrogen ions produced in the light-dependent reaction of photosynthesis.
• What is oxidation?


  Oxidation is the loss of electrons or hydrogen atoms, or the gain of oxygen atoms.
• What is reduction?


  Reduction is the gain of electrons or hydrogen atoms, or the loss of oxygen atoms.
• What is the photolysis of water?


  When light splits water, creating H+ ions, electrons, and oxygen.
• Why is photolysis essential?


  Electrons replenish those lost from chlorophyll (in PSII). Protons are pumped across the thylakoid membrane ready to move through ATP synthase.
• What is chemiosmosis?


  The movement of protons against their gradient across the thylakoid membrane, building up a high concentration so they can then move through ATP synthase and create ATP. It is not called active transport as the energy to move the protons against their concentration gradient comes from the electrons moving from carrier to carrier in series of redox reactions and not from ATP being hydrolysed.
• What molecules are needed to produce on ATP?


  ADP + PI - we can say the ADP has been phosphorylated.
• Describe the light dependent reaction.


  -Light hits chlorophyll and excites electrons which are lost from chlorophyll (photoionisation).

  -Electrons accepted by electron carrier, move from carrier to carrier in a series of redox reactions.

  -Energy released from electrons during redox reactions pumps protons into thylakoid space (chemiosmosis).

  -Protons move through ATP synthase and ATP is produced.

  -Electron and proton accepted by NADP to form reduced NADP.

  -Photolysis of water occurs - producing protons and electrons needed in other parts of the reaction.

  -Oxygen is produced as waste.
• Where in the chloroplast would you find RUBISCO?


  The stroma.
• What is the other name for the light independent reaction?


  The Calvin Cycle.
• Describe the light independent reaction.


  -RuBP (5C) joins with CO2 to make two glycerate phosphate ( 2 x 3C).

  -GP are reduced into triose phosphate (2 x 3C).

  -This transfers energy from hydrolysis of ATP and oxidises the reduced NADP back to NADP.

  -Two TP can be used to reform RuBP (5C) which transfers energy from hydrolysis of ATP.

  -The one carbon remaining after each of the 6 cycles of the LIR is used to form glucose (6C organic molecules).
• How are other organic molecules made in plants?


  GP can be used to form amino acids and fatty acids. TP can be used to form glycerol.
• Why does light limit the light independent stage?

  No photolysis or photoionisation would occur. No ATP or reduced NADP made in LDR therefore GP cannot be converted to TP. RuBP wouldn't be regenerated from TP as ATP isn't available.
• Why does carbon dioxide limit the light independent stage?

  RuBP cannot be converted into GP, so no reduction of GP to TP and no glucose made.
• Why is respiration so important for cells?


  Production of ATP which is needed for cellular metabolic reactions and cannot be moved from cell to cell (so each cell has to generate its own supply of ATP).
• What makes ATP a good source of energy?


  It's an immediate energy source of energy as only a single bond need to be broken. It releases a small, manageable amount of energy required for a specific reaction. It is quickly regenerated as only a single bond needs to be reformed.
• What are the stages of aerobic respiration?

  Glycolysis, Link Reaction, Krebs Cycle, Oxidative Phosphorylation.
• What is the difference between aerobic and anaerobic respiration?


  Aerobic uses oxygen and produces a lot of ATP as all four stages can occur; anaerobic does not use oxygen and produces only a little ATP during glycolysis.
• Where does aerobic respiration take place?


  Glycolysis happens in the cytoplasm, Link and Krebs in the mitochondrial matrix, and Oxidative Phosphorylation at the cristae (inner mitochondrial membrane).
• How much ATP is created in aerobic and anaerobic respiration?


  38 ATP molecules in aerobic, 2 ATP molecules in anaerobic.
• What are the end products of aerobic respiration?


  Carbon dioxide and water.
• What are the end products of anaerobic respiration?


  Lactate in animals, ethanol in plants and fungi.
• What is the role of NAD?


  NAD is a molecule that carries electrons and hydrogen ions during aerobic respiration.
• What are the stages of glycolysis?


  1. Phosphorylation of glucose
  2. Production of triose phosphate
  3. Oxidation of triose phosphate to pyruvate
• How is glucose converted to glucose phosphate?


  2 ATP molecules undergo hydrolysis to become 2 ADP. The two phosphate molecules bond to the glucose, which lowers the activation energy for the next stage.
• How is triose phosphate created?


  Glucose phosphate (6C) is unstable so it splits to become two molecules of triose phosphate (2 x 3C).
• How is triose phosphate converted to pyruvate?


  A hydrogen molecule is removed when each triose phosphate is oxidised by NAD to make reduced NAD. 2 ADP molecules react with the triose phosphate to become 2 ATP molecules (ADP are phosphorylated). This leaves behind 2 pyruvate.
• How many ATP molecules are created during glycolysis?


  Four, though two are needed to phosphorylate glucose, making a net gain of two.
• What is the net output of glucose?


  2 ATP

  2 Pyruvate

  2 reduced NAD
• In anaerobic respiration, what happens to pyruvate?


  It is reduced to ethanol and CO2 in plants and fungi, or lactate in animals.
• In anaerobic respiration, what happens to the reduced NAD?


  It becomes oxidised back to NAD as it is used to reduce the pyruvate. The NAD can then be used again in glycolysis.
• In aerobic respiration, what happens to pyruvate?


  It is taken into the mitochondrial matrix in order to take part in the link reaction.
• What is the name of the reaction that uses the pyruvate from glycolysis?


  The Link Reaction.