7.3.1 Lactate after anaerobic respiration Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 7

The 20 questions

1. In anaerobic respiration in animals, pyruvate is converted to lactate by:

   • ATP synthase, which uses the proton gradient to add a phosphate group to pyruvate
   • Pyruvate decarboxylase, which removes carbon dioxide from pyruvate to form ethanol
   • Acetyl CoA synthase, which joins pyruvate to coenzyme A to start the Krebs cycle
   • Lactate dehydrogenase, which uses reduced NAD to reduce pyruvate and regenerates NAD+

2. Why is lactate production important during anaerobic respiration?

   • It converts glucose into glycogen for storage, which is needed for the next period of activity
   • It removes carbon dioxide from the muscle, which otherwise would reduce the pH of the cell
   • It produces large amounts of ATP directly, more than any aerobic step in the mitochondria
   • It regenerates NAD+ so that glycolysis can continue to produce ATP when oxygen is scarce

3. After a period of anaerobic exercise, lactate is most commonly:

   • Converted into carbon dioxide in the sarcoplasmic reticulum, which then leaves the cell
   • Transported in the blood to the liver, where it can be converted back to glucose or glycogen
   • Excreted immediately in the urine, without any change to its chemical structure
   • Stored permanently in the muscle fibre, where it is never used again by any tissue

4. Which organ is the main site where lactate is converted back into glucose in the body?

   • The heart, which oxidises lactate completely to carbon dioxide and water in every beat
   • The kidney, which filters lactate out of the blood and converts it into urea
   • The liver
   • The brain, which uses lactate as its main fuel and converts it to glucose in the neurones

5. The oxygen needed to repay an oxygen debt after exercise is used mainly to:

   • Produce carbon dioxide in the sarcoplasmic reticulum, which is then used to regenerate ATP
   • Produce lactate from pyruvate in the cytoplasm, which then acts as a store for future exercise
   • Split glucose into two pyruvate molecules during the first step of glycolysis in the cytoplasm
   • Oxidise lactate and resynthesise phosphocreatine and glycogen, restoring the body to its resting state

6. A runner's blood lactate concentration rises sharply during a 400 m sprint. What is the most likely explanation?

   • The lungs are releasing lactate into the blood to remove carbon dioxide from the tissues
   • Glycolysis is producing pyruvate faster than oxygen can be delivered for aerobic respiration
   • The liver is converting glucose to lactate continuously, regardless of the energy demand
   • The muscles are producing lactate from fat, which is faster than any carbohydrate pathway

7. Which statement about lactate and the Cori cycle is correct?

   • Lactate from the blood is converted directly to ATP in the brain without any further steps
   • Lactate from the kidney is converted into pyruvate, which enters the Krebs cycle in the liver
   • Lactate from the liver is transported to the muscle and converted to carbon dioxide and water
   • Lactate from muscle is transported to the liver and converted back to glucose

8. Which molecule is reduced to form lactate during anaerobic respiration?

   • Pyruvate, which accepts hydrogen from reduced NAD
   • Carbon dioxide, which accepts hydrogen from reduced NAD to form glucose
   • Oxygen, which accepts hydrogen from reduced NAD to form water in the matrix
   • Glucose, which accepts hydrogen from reduced FAD in the cytoplasm of the cell

9. Why is lactate production described as a way of regenerating NAD+?

   • Because reduced NAD gives its hydrogen to pyruvate
   • Because NAD+ is produced from carbon dioxide, which is reduced by lactate in the cytoplasm
   • Because NAD+ is released when lactate is oxidised in the mitochondria during recovery
   • Because NAD+ is made from lactate in the liver, which then returns it to the muscle

10. Which of the following is the main reason that anaerobic respiration cannot be sustained for long periods?

    • Anaerobic respiration stops the heart from beating, which prevents oxygen from reaching muscles
    • Lactate accumulates and lowers the pH of the muscle
    • Lactate is converted to carbon dioxide, which poisons the mitochondria within a few seconds
    • Anaerobic respiration uses up all the oxygen in the blood, so the muscle cannot continue to respire

11. What does oxygen debt represent after exercise?

    • It is the oxygen that is stored in the muscle during exercise and is used up during the activity
    • It is the extra oxygen consumed after exercise to restore the body to its resting state
    • It is the oxygen that is needed to produce lactate during the first minute of anaerobic exercise
    • It is the oxygen that is lost from the blood during exercise because of the high rate of breathing

12. A student claims that lactate is a waste product that the body cannot use. Which statement best evaluates this claim?

    • The claim is accurate, since lactate is a toxin that is removed by the lungs as carbon dioxide
    • The claim is inaccurate, since lactate is transported to the liver and heart and can be converted back to glucose or oxidised
    • The claim is accurate, since lactate is excreted from the body in urine without any further use
    • The claim is inaccurate, since lactate is converted into oxygen in the muscle, which is then used for respiration

13. Which statement describes the effect of blocking lactate dehydrogenase during intense anaerobic exercise?

    • NAD+ is regenerated faster, so glycolysis speeds up and the rate of ATP production rises
    • NAD+ cannot be regenerated, so glycolysis slows and the rate of ATP production falls
    • Pyruvate is converted to carbon dioxide, which increases the rate of ATP production
    • Lactate builds up in the mitochondria, which then increases the rate of the Krebs cycle

14. Which statement about muscle fatigue is most consistent with the role of lactate?

    • Lactate causes fatigue by binding to tropomyosin, which permanently blocks the myosin heads
    • Lactate has no link to fatigue, since fatigue is caused only by a lack of calcium in the sarcoplasm
    • Accumulation of lactate and hydrogen ions is associated with fatigue, through a fall in pH within the muscle
    • Accumulation of lactate increases the pH of the muscle, which makes the muscle contract more strongly

15. Why is lactate formed in the cytoplasm rather than in the mitochondria?

    • Lactate formation requires the Krebs cycle enzymes, which are found only in the cytoplasm of the cell
    • Lactate formation requires the inner membrane of the mitochondrion, which is absent from the cytoplasm
    • Lactate formation requires the electron transport chain, which is located in the cytoplasm
    • Lactate formation is a continuation of glycolysis, which takes place in the cytoplasm

16. A sprinter's muscle contains many fast twitch fibres. Why would this increase lactate production during a short race?

    • Fast twitch fibres have high myoglobin content, which converts oxygen into lactate during contraction
    • Fast twitch fibres rely on glycolysis and produce pyruvate faster than the mitochondria can oxidise it
    • Fast twitch fibres have many mitochondria that release lactate as a by-product of the Krebs cycle
    • Fast twitch fibres do not respire at all, so lactate is the only product of their energy release

17. Which statement describes the energy yield of anaerobic respiration in animals compared with aerobic respiration?

    • Anaerobic respiration yields no ATP at all, since only aerobic respiration can make ATP in animal cells
    • Anaerobic respiration yields the same ATP per glucose, because the same electron transport chain is used
    • Anaerobic respiration yields far less ATP per glucose
    • Anaerobic respiration yields more ATP per glucose, because lactate is a higher-energy molecule than glucose

18. Which statement evaluates the claim that lactate production is always harmful to athletes?

    • The claim is oversimplified, since lactate can be reused as fuel and its production sustains ATP supply in intense effort
    • The claim is accurate, since lactate is always converted into toxic carbon monoxide in the muscle
    • The claim is inaccurate, since lactate is never produced by athletes because they respire only aerobically
    • The claim is accurate, since lactate production always stops all ATP production in every athlete

19. Which statement about lactate in heart muscle is accurate?

    • Heart muscle can oxidise lactate supplied in the blood as a fuel, using aerobic respiration
    • Heart muscle cannot use lactate at all and excretes it in sweat during exercise
    • Heart muscle converts lactate into glucose, which it stores as glycogen for later use
    • Heart muscle uses lactate only during fasting and never during periods of exercise

20. What is the advantage of lactate being transported in the blood rather than staying in the working muscle?

    • It stops the heart rate from rising during exercise, which conserves energy in the muscle
    • It binds permanently to haemoglobin, so that oxygen can no longer be carried in the blood
    • It causes the blood to clot, which stops oxygen reaching the working muscle during exercise
    • Other tissues and the liver can remove it, reducing its build-up in the working muscle

Related quizzes

• Why animals need a circulation and the role of water Quiz · 1.1.1 · 20 questions
• Gas exchange surfaces and Fick's Law Quiz · 2.1.1 · 20 questions
• Common features of living cells Quiz · 3.1.1 · 20 questions
• Biodiversity, endemism and threats to variety of life Quiz · 4.1.1 · 20 questions
• Ecosystems, communities, populations and biotic and abiotic factors Quiz · 5.1.1 · 20 questions
• Time of death, decomposition and forensic entomology Quiz · 6.1.1 · 20 questions
• Structure and function of blood vessels Quiz · 1.1.2 · 20 questions
• Cell membrane structure and the fluid mosaic model Quiz · 2.1.2 · 20 questions
• Eukaryotic ultrastructure and electron micrographs Quiz · 3.1.2 · 20 questions
• Measuring biodiversity: heterozygosity and diversity index Quiz · 4.1.2 · 20 questions