exam qs

• Describe the process of glycolysis (4)

  • Phosphorlyation of glucose using ATP
  • Oxidation of triose phosphate to pyruvate
  • Net gain of ATP - 4 produced and 2 used
  • NAD reduced to NADH+
• Malonate inhibits a reaction in the Krebs cycle.

  Explain why malonate would decrease the uptake of oxygen in a respiring cell (2)

  • less reduced NAD
  • oxygen is the terminal electron acceptor
• Anaerobic respiration does not use oxygen as its final electron acceptor so less ATP can be made compared with aerobic respiration.
• Name the substances formed from pyruvate

  • CO2
  • water
  • ATP
  • reduced NAD/FAD
• If there is a shortage of oxygen in muscle cells during exercise, some pyruvate is converted into lactate. Explain why muscles become fatigued when insufficient oxygen is available (2).

  • `build up of lactate lowers pH/increases acidity
  • enzymes inhibited
• Some of the lactate is oxidised to pyruvate by muscles when they are well-supplied with oxygen.

  Suggest an advantage of the lactate being oxidised in the muscles. (2)

  • pyruvate is an energy source
  • muscles have increased ATP supply
  • restores pH levels
• Explain why converting pyruvate to ethanol is important in allowing the continued production of ATP in anaerobic conditions. (2)

  • allows NAD to be recycled / re-formed
  • so that glycolysis can proceed / so that more glucose can be converted to pyruvate
• Give ways in which anaerobic respiration of glucose in yeast is similar to anaerobic respiration of glucose in a muscle cell.

  • ATP formed
  • pyruvate formed / reduced
  • NAD / reduced NAD
  • glycolysis involved / two step process
• Give ways in which anaerobic respiration of glucose in yeast is different from anaerobic respiration of glucose in a muscle cell

  • ethanol formed by yeast, lactic acid formed by muscle cells
  • CO2 released by yeast but not by muscle cell
• Give two ways in which the properties of ATP make it a suitable source of energy in biological processes (2)

  • soluble
  • energy released in small / suitable amounts
  • involves a single / simple reaction
• ATP is useful in many biological processes. Explain why. (4)

  • Releases energy in small /manageable amounts
  • (Broken down) in a one step / single bond broken
  • Immediate energy compound / makes energy available rapidly
  • Phosphorylates / adds phosphate
  • Makes (phosphorylated substances) more reactive / lowers activation energy
  • Reformed again
• Humans synthesise more than their body mass of ATP each day. Explain why it is necessary for them to synthesise such a large amount of ATP. (2)

  1. ATP is unstable
  2. ATP cannot be stored / is an immediate source of energy
  3. ATP only releases a small amount of energy at a time
• Describe how acetylcoenzyme A is formed in the link reaction. (2)

  1. Oxidation of / hydrogen removed from pyruvate and carbon dioxide released
  2. Addition of coenzyme A.
• Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration. (2)

  1. Regenerates / produces NAD / oxidises reduced NAD
  2. (NAD used) in glycolysis.
• In muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen. Suggest one advantage of this. (1)

  • (Pyruvate used) in aerobic respiration
  • (lactate) is toxic / harmful / causes cramp / (muscle) fatigue.
• How does DNP cause less ATP to be produced, more heat to be produced and the uptake of oxygen to remain constant?

  1. Less / no proton / H+ movement so less / no ATP produced
  2. Heat released from electron transport / redox reactions / energy not used to produce ATP is released as heat
  3. Oxygen used as final electron acceptor / combines with electrons (and protons)
• Respiration produces more ATP per molecule of glucose in the presence of oxygen than it does when oxygen is absent. Explain why. (2)

  1. Oxygen is final / terminal (electron) acceptor / oxygen combines with electrons and protons
  2. Oxidative phosphorylation / electron transport chain provides (most) ATP / only glycolysis occurs without oxygen / no Krebs / no link reaction
• What is the main difference between the way in which ATP is produced by oxidative phosphorylation and the way in which it is produced in photosynthesis?

  Energy from chemical reaction/ oxidation/ not from light
• Red blood cells do not contain mitochondria but they use ATP. By what process do red blood cells produce ATP? Suggest a reason for your answer.

  • Glycolysis / anaerobic respiration
  • Does not occur in mitochondria / takes place in cytoplasm
• During glycolysis, NAD is reduced. Explain what happens to this reduced NAD when the cell is respiring anaerobically.

  • Converted back to NAD / is dehydrogenated / H+ removed / is oxidised
  • Passes H to pyruvate / reduces pyruvate / produces lactate
• Describe what happens to pyruvate in anaerobic conditions and explain why anaerobic respiration is advantageous to human skeletal muscle. (4)

  • Forms lactate
  • Use of reduced NAD / NADH
  • Regenerates NAD
  • NAD can be re-used to oxidise more respiratory substrate
  • Can still release energy / form ATP when oxygen is in short supply / when no oxygen
• Describe how NAD is regenerated in anaerobic respiration in yeast cells.

  Formed when reduced NAD used to reduce / donate H ions to pyruvate / convert pyruvate to ethanol
• Explain why converting pyruvate to ethanol is important in allowing the continued production of ATP in anaerobic respiration.

  • allows NAD to be recycled / re-formed
  • so that (more) glucose can be converted to pyruvate
• Give two ways in which anaerobic respiration of glucose in yeast is similar to anaerobic respiration of glucose in a muscle cell

  • ATP formed / used
  • pyruvate formed / reduced
  • NAD / reduced NAD
  • glycolysis involved
• Give two ways in which anaerobic respiration of glucose in yeast is different to anaerobic respiration of glucose in a muscle cell

  • ethanol / alcohol formed by yeast, lactate by muscle cell
  • CO2 released by yeast but not by muscle cell
• Describe the part played by oxygen in the process of aerobic respiration. (2)

  • Terminal hydrogen / electron acceptor
  • producing water / a safe end product
• Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion. (3)

  • ATP formed as electrons pass along transport chain
  • oxygen is terminal electron acceptor
  • electrons cannot be passed along electron transport chain if no oxygen to accept them
  • forms water
• How many molecules of ATP are produced from each glucose molecule in anaerobic respiration?

  2
• Explain why ATP is necessary for glycolysis.

  phosphorylate
• Describe how oxidation takes place in glycolysis and in the Krebs cycle. (3)

  • removal of hydrogen
  • by enzymes
  • H+ accepted by NAD / reduced NAD formed
  • in Krebs cycle, FAD (used as well)
• Water is a waste product of aerobic respiration. Describe how water is formed at the end of aerobic respiration. (2)

  • oxygen is terminal / final electron acceptor
  • combines with electron and hydrogen (to form water)
• Explain the advantage of mitochondria in muscle cells having more cristae.

  • (larger surface area) for electron transport chain /more enzymes for ATP production / oxidative phosphorylation
  • muscle cells use more ATP
• Describe what happens in the link reaction

  • carbon dioxide formed
  • hydrogen released / reduced NAD formed
  • acetyl coenzyme A produced
• Describe the roles of the coenzymes and carrier proteins in the synthesis of ATP in the Kreb's cycle (3)

  • NAD / FAD reduced
  • electrons transferred from coenzyme to coenzyme / series of redox reactions
  • energy made available as electrons passed on
  • energy used to synthesise ATP from ADP and phosphate
  • H+ / protons passed into intermembrane space
  • H+ / protons flow back through enzyme
• Aerobic respiration produces more ATP per molecule of glucose than anaerobic respiration. Explain why. (2)

  • oxygen is the final / terminal electron acceptor
  • oxidative phosphorylation only in aerobic respiration
  • anaerobic respiration only glycolysis occurs
• Describe the part played by the inner membrane of a mitochondrion in producing ATP (3)

  • Electrons are transferred down the electron transport chain
  • Provides energy to actively transport protons into space between membranes
  • protons then diffuse back through the membrane via ATPase
• If most of the mitochondria in a cell are faulty, this prevents many important enzyme-catalysed reactions taking place or slows them down.

  Suggest and explain one reason why. (2)

  • not enough / little ATP produced
  • ATP provides energy for enzyme reactions / ATP phosphorylates substrates so making them more reactive