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Cambridge IGCSE0610

Respiration

Biology 0610 Chapter Notes

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RespirationAerobic respirationAnaerobic respiration
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In this chapter

  1. 1Respiration releases energy
  2. 2Energy for muscles, proteins, division and transport
  3. 3Energy for growth, nerves and body temperature
  4. 4Processes that do not use this energy
  5. 5Investigating temperature in yeast: change and measure
  6. 6Keeping the test fair
  7. 7Writing the conclusion
  8. 8What aerobic respiration is
  9. 9Energy is released, not made
  10. 10The word equation
  11. 11The balanced chemical equation
  12. 12Using the balanced equation
  13. 13What anaerobic respiration is
  14. 14Anaerobic respiration in yeast
  15. 15Anaerobic respiration in muscles
  16. 16The balanced equation for yeast
  17. 17Lactic acid and oxygen debt
  18. 18Removing the oxygen debt

1. Respiration releases energy

Respiration is a chemical reaction in cells that breaks down nutrient molecules to release energy.

Energy is released. It is never made or produced. Every use of energy in the next three sections starts here.

Examiner insight

“Candidates should be reminded that energy is released not produced or made.” “One misconception is that energy is required for respiration rather than released by respiration.”

Worked example 11 mark

Which characteristic of living things is described as the breakdown of nutrient molecules to release energy?

A excretion · B nutrition · C respiration · D sensitivity

  1. 1

    C: respiration. [1]

2. Energy for muscles, proteins, division and transport

The energy released by respiration is used for muscle contraction, protein synthesis, cell division and active transport.

Name the process. Give a use of energy, not a use of oxygen.

Examiner insight

“The most common correct answer was active transport. Protein synthesis was less well known.” “Errors include giving uses of oxygen rather than uses of energy.”

Worked example 13 marks

State three uses of the energy released by respiration.

  1. 1

    muscle contraction [1]

  2. 2

    protein synthesis [1]

  3. 3

    cell division [1]

  4. 4

    Any three of the seven uses earn the marks.

3. Energy for growth, nerves and body temperature

Energy from respiration is also used for growth, for the passage of nerve impulses and for the maintenance of a constant body temperature.

These three are easy to forget. Learn all seven uses as one list.

Examiner insight

“The fact that growth is a process that uses energy released by respiration was not well-known.” “The most common correct example of energy usage was muscle contraction; the conduction of nerve impulses was seen less frequently.”

Worked example 12 marks

A young mammal is growing in a cold place. Its body temperature stays constant. State two uses of the energy released by respiration that this shows.

  1. 1

    growth [1]

  2. 2

    maintenance of a constant body temperature [1]

4. Processes that do not use this energy

Diffusion and osmosis do not use energy from respiration. Active transport does.

Sort each process before choosing an answer. A process that sounds like movement is not always one that needs energy.

Examiner insight

“This proved to be a very demanding question, with most candidates not appreciating that diffusion does not require energy released by respiration.” “Many candidates did not appreciate that while the production of new red blood cells and the transmission of nerve impulses use energy released by respiration, the diffusion of gases does not.”

Worked example 11 mark

What are ways in which energy from respiration is used in living organisms?

key

checkmark = energy is used for this

× = energy is not used for this

active transportdiffusionosmosisprotein synthesis
Acheckmarkcheckmarkcheckmark×
Bcheckmark××checkmark
Ccheckmark×checkmarkcheckmark
D×checkmark×checkmark
  1. 1

    Active transport and protein synthesis use energy from respiration. Diffusion and osmosis do not.

  2. 2

    B [1]

5. Investigating temperature in yeast: change and measure

To investigate the effect of temperature on respiration in yeast, change the temperature and measure the gas the yeast gives off.

The independent variable is temperature: use at least two different temperatures, held in a thermostatically controlled water-bath. The dependent variable is the number of bubbles or the volume of gas, carbon dioxide, produced.

Examiner insight

“Using a gas syringe was the most common correct answer. Some candidates stated that a measuring cylinder could be used, but failed to qualify this with any details of a displacement method or of collecting over water which should have been described.” “Simply stating that temperature would be kept the same is insufficient and a method needs to be described, such as the use of a thermostatically controlled water-bath or the addition of insulation.”

Worked example 16 marks

Plan an investigation to determine the effect of temperature on the rate of respiration in yeast.

  1. 1

    independent variable: at least two different temperatures [1]

  2. 2

    dependent variable: number of bubbles, or volume of gas / carbon dioxide, produced [1]

  3. 3

    method: use of a thermostatically controlled water-bath [1]

  4. 4

    method: gas syringe, or collecting the gas over water, to measure the volume of gas [1]

  5. 5

    variable kept constant: volume of yeast [1]

  6. 6

    at least three trials [1]

6. Keeping the test fair

Keep every other variable constant. Name it exactly: the volume of yeast, the type of yeast, or the volume and concentration of the sugar solution.

Allow time for equilibration before measuring: the yeast is left to reach the temperature of the surrounding water. Measure over a set time period. Make at least three trials, and add a relevant safety precaution.

Stir the yeast suspension first. Stirring gives an even distribution of the yeast cells.

Examiner insight

“Candidates are reminded to be specific in their answers. Yeast unqualified is insufficient to gain credit.” “An answer of time was not enough for the mark. Candidates either needed to give the time for equilibration or the time for counting bubbles as their answer.”

Worked example 12 marks

A student compares yeast at two temperatures. State two variables that must be kept constant.

  1. 1

    the volume of yeast (not just ‘yeast’) [1]

  2. 2

    the volume of sugar solution [1]

7. Writing the conclusion

A conclusion links the independent variable to the dependent variable. Here that means temperature and the rate of respiration.

The higher the temperature, the higher the rate of respiration. The bubbles are only how you measure it.

rate of bubble production = (number of bubbles)/time

Examiner insight

“A conclusion should relate the independent variable to the dependent variable.” “The most common error was to describe the results in terms of the number of bubbles instead of the rate of respiration.”

Worked example 13 marks

A student counts the bubbles of gas that yeast gives off in 2 minutes at three temperatures. State a conclusion, using the data. Then calculate the rate of bubble production at 40 °C.

temperature / °Cnumber of bubbles in 2 minutes
206
3018
4042
  1. 1

    The higher the temperature, the higher the rate of respiration of yeast. [1]

  2. 2

    data: bubbles in 2 minutes rise from 6 at 20 °C to 42 at 40 °C [1]

  3. 3

    rate = 42 ÷ 2 = 21 bubbles per minute [1]

Recap

  • Respiration is a chemical reaction in cells that breaks down nutrient molecules to release energy. Energy is released, never produced.
  • Uses of the energy: muscle contraction, protein synthesis, cell division, active transport, growth, the passage of nerve impulses, the maintenance of a constant body temperature.
  • Diffusion and osmosis do not use energy from respiration.
  • Yeast and temperature: change the temperature, use at least two temperatures, measure bubbles or volume of gas.
  • Keep constant: volume of yeast, volume of sugar solution. Name each one. Allow time for equilibration. Make at least three trials.
  • Conclusion: the higher the temperature, the higher the rate of respiration.

8. What aerobic respiration is

Aerobic respiration is the chemical reactions in cells that use oxygen to break down nutrient molecules to release energy.

It takes place in the mitochondria. Give the full term, aerobic respiration, not just "respiration".

Examiner insight

“Some candidates were vague in their responses and simply gave the name of the process as respiration.”

Worked example 11 mark

In which part of the cell does aerobic respiration occur?

A cytoplasm · B mitochondrion · C ribosome · D vesicle

  1. 1

    B: mitochondrion. [1]

9. Energy is released, not made

Aerobic respiration releases energy from nutrient molecules such as glucose. It does not produce energy.

Muscle cells use the energy released for muscle contraction. When muscles contract more, the rate of aerobic respiration increases to release the energy they need.

Examiner insight

“One misconception was that mitochondria ‘produce’ energy rather than releasing energy.”

Worked example 12 marks

Horses are mammals that have similar breathing and circulatory systems to humans. During the race the rate of respiration changes. Explain why the rate of aerobic respiration increases at the start of the race.

  1. 1

    to release energy [1]

  2. 2

    for muscle contraction [1]

10. The word equation

Glucose and oxygen are the reactants: they are used up. Carbon dioxide and water are the products: they are made.

Learn the equation in this order, with the reactants on the left.

glucose + oxygen → carbon dioxide + water

Examiner insight

“While many candidates correctly identified the word equation for aerobic respiration, some incorrectly chose the word equation for photosynthesis, option A.” “Carbon dioxide and glucose were the commonest incorrect response.”

Worked example 11 mark

Which row describes the aerobic respiration of glucose?

carbon dioxide producedenzymes are requiredoxygen requiredwater produced
Ayesyesyesyes
Byesnoyesyes
Cnoyesnoyes
Dnonoyesno
  1. 1

    A: carbon dioxide is produced, enzymes are required, oxygen is required and water is produced. [1]

11. The balanced chemical equation

The balanced chemical equation uses the formula of each substance: glucose is C₆H₁₂O₆, oxygen is O₂, carbon dioxide is CO₂ and water is H₂O.

The numbers in front balance it. Each side has 6 carbon atoms, 12 hydrogen atoms and 18 oxygen atoms.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

Examiner insight

“Some incorrectly gave the equation for photosynthesis.”

Worked example 12 marks

State the balanced equation for aerobic respiration.

  1. 1

    C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O [2]

12. Using the balanced equation

The numbers in the balanced equation give the ratio of molecules. One molecule of glucose needs 6 molecules of oxygen and makes 6 molecules of carbon dioxide and 6 of water.

For more glucose, multiply every number by the number of glucose molecules.

Examiner insight

“Many candidates correctly worked out that 18 molecules of oxygen are required for the aerobic respiration of three molecules of glucose. The commonest incorrect response was to give the value for one molecule of glucose.” “Since one molecule of glucose yields six molecules of carbon dioxide, then three molecules of glucose yield eighteen molecules of carbon dioxide.”

Worked example 12 marks

How many molecules of oxygen are needed for the aerobic respiration of 3 molecules of glucose?

  1. 1

    C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O: 1 glucose needs 6 oxygen [1]

  2. 2

    3 × 6 = 18 molecules of oxygen [1]

Recap

  • Aerobic respiration is the chemical reactions in cells that use oxygen to break down nutrient molecules to release energy.
  • It takes place in the mitochondria.
  • Energy is released, not produced. It is used for muscle contraction.
  • Word equation: glucose + oxygen → carbon dioxide + water.
  • Extended: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.
  • Extended: 1 glucose needs 6 oxygen and makes 6 carbon dioxide and 6 water. Multiply for more glucose.

13. What anaerobic respiration is

Anaerobic respiration is the chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.

It releases much less energy per glucose molecule than aerobic respiration.

Energy is released, not produced or made.

Examiner insight

“Some candidates were confused about the role of energy in respiration. Energy is released but is not produced in respiration.” “Candidates should be reminded that the process of respiration releases energy and does not produce energy.”

Worked example 13 marks

Circle the correct word or phrase to make three correct sentences about respiration.

Respiration is a chemical reaction in cells that breaks down all / nutrient / waste molecules to release energy.

Compared to aerobic respiration, anaerobic respiration releases less / more / the same amount of energy per molecule respired.

Aerobic respiration occurs in chloroplasts / mitochondria / vacuoles.

  1. 1

    nutrient [1]

  2. 2

    less [1]

  3. 3

    mitochondria [1]

14. Anaerobic respiration in yeast

Yeast cells respire anaerobically to make alcohol and carbon dioxide.

The reactant is glucose. Lactic acid is not made by yeast.

glucose → alcohol + carbon dioxide

Examiner insight

“A small proportion of candidates stated a correct word equation for anaerobic respiration in yeast. The majority included lactic acid in the equation or did not include glucose as a reactant.” “There was some uncertainty over the products of anaerobic respiration in yeast. The products are alcohol and carbon dioxide.”

Worked example 11 mark

Which cells produce carbon dioxide during anaerobic respiration?

rowmuscle cellsyeast cells
Anono
Bnoyes
Cyesno
Dyesyes
  1. 1

    B: yeast cells make carbon dioxide (glucose → alcohol + carbon dioxide); muscle cells do not [1]

15. Anaerobic respiration in muscles

During vigorous exercise, muscle cells respire anaerobically to make lactic acid only.

The reactant is glucose. No carbon dioxide is made, and no alcohol.

glucose → lactic acid

Examiner insight

“There was some uncertainty about anaerobic respiration in muscles. Lactic acid is the only product.” “Many candidates did not know that carbon dioxide is not produced in anaerobic respiration in humans.”

Worked example 11 mark

Which row describes anaerobic respiration in humans?

rowcarbon dioxide producedoxygen neededamount of energy released compared to aerobic respiration
Ayesyeshigh
Byesnolow
Cnoyeshigh
Dnonolow
  1. 1

    D: no carbon dioxide (only lactic acid), no oxygen needed, and low energy released [1]

16. The balanced equation for yeast

The balanced chemical equation for anaerobic respiration in yeast has ethanol and carbon dioxide as products.

One glucose molecule makes two molecules of each. There is no oxygen on the left-hand side.

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

Examiner insight

“However, many did not write the formula for ethanol correctly or did not balance the equation. Some rewrote the question by adding 6O2 to glucose and completing the equation for aerobic respiration.”

Worked example 11 mark

Which reaction does this balanced chemical equation show?

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

A aerobic respiration

B anaerobic respiration in muscles

C anaerobic respiration in yeast

D photosynthesis

  1. 1

    C: glucose makes ethanol and carbon dioxide with no oxygen, so it is anaerobic respiration in yeast [1]

17. Lactic acid and oxygen debt

During vigorous exercise, lactic acid builds up in the muscles and blood.

This causes an oxygen debt.

Examiner insight

“Some candidates gave the incorrect product of carbon dioxide rather than lactic acid.” “The correct answer of lactic acid was commonly seen. The most common incorrect response being carbon dioxide.”

Worked example 12 marks

During a sprint, a runner's muscles respire anaerobically.

(a) Name the substance that builds up in the muscles and blood.

(b) State the term for the result of this build-up.

  1. 1

    (a) lactic acid [1]

  2. 2

    (b) oxygen debt [1]

18. Removing the oxygen debt

After exercise, three things remove the oxygen debt.

The heart rate stays fast, to carry lactic acid in the blood from the muscles to the liver.

Breathing stays deeper and faster, to supply oxygen. In the liver, the lactic acid is broken down by aerobic respiration.

Examiner insight

“In outlining how the body removes an oxygen debt, few candidates mentioned that the breathing rate and heart rate remain high, most stating that both increased.” “Some candidates incorrectly believed that anaerobic respiration of lactic acid in the muscles takes place.”

Worked example 11 mark

The heart rate in humans remains high for a period of time after exercise.

Which statement explains why?

A Carbon dioxide needs to be transported from the lungs to the liver.

B Glucose needs to be transported from the muscles to the liver.

C Lactic acid needs to be transported from the muscles to the liver.

D Oxygen needs to be transported from the liver to the lungs.

  1. 1

    C: the fast heart rate carries lactic acid from the muscles to the liver [1]

Recap

  • Anaerobic respiration: chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.
  • It releases much less energy per glucose molecule than aerobic respiration.
  • Yeast: glucose → alcohol + carbon dioxide.
  • Muscles in vigorous exercise: glucose → lactic acid.
  • Extended: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ for yeast.
  • Extended: lactic acid builds up in muscles and blood and causes an oxygen debt.
  • Extended: the debt is removed by a fast heart rate, deeper and faster breathing, and aerobic respiration of lactic acid in the liver.

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. A student writes: “Respiration produces energy.” Correct the sentence.1 mark
  2. State two uses of the energy released by respiration in a growing child.2 marks
  3. Which two of these processes use energy released by respiration: diffusion, osmosis, protein synthesis, cell division?2 marks
  4. Root hair cells take in mineral ions by active transport. Explain why root hair cells need respiration.2 marks
  5. A student investigates the effect of temperature on respiration in yeast. State the independent variable, the dependent variable and one variable kept constant.3 marks
  6. A student measures the gas given off by yeast. State two ways of measuring the volume of the gas.2 marks
  7. A student counts the bubbles of gas that yeast gives off in 3 minutes. The yeast gives off 9 bubbles at 15 °C, 30 bubbles at 25 °C and 66 bubbles at 35 °C. (a) Calculate the rate of bubble production at 35 °C. [1] (b) State a conclusion for this investigation. Support it with data. [2]3 marks
  8. A student puts test-tubes of yeast into a beaker of warm water and starts counting bubbles at once. Suggest two improvements to the method.2 marks
  9. A baker tests a dried yeast. She stirs a yeast suspension, then puts 10 cm³ of it into each of two syringes. Syringe P goes into water at 16 °C and syringe Q into water at 32 °C. She waits 3 minutes. She then counts the bubbles of gas from each syringe for the next 5 minutes. P gives 15 bubbles and Q gives 65 bubbles. (a) Explain why she stirs the suspension before filling the syringes. [1] (b) Explain why she waits 3 minutes before counting. [1] (c) Calculate the rate of bubble production for each syringe. [2] (d) State the conclusion. [1]5 marks
  10. A student investigates the effect of temperature on the rate of respiration in yeast. The gas is collected in a gas syringe. Each temperature is tested once. The table gives the results. (a) Calculate the rate of gas production at each temperature. [2] (b) The student says that the rate of respiration is higher at 24 °C than at 12 °C. Explain whether the results support this. [2] (c) Explain why the result at 36 °C cannot be fairly compared with the other two results. [1] (d) State one other improvement to the method. [1] | temperature / °C | volume of yeast suspension / cm³ | time of collection / minutes | volume of gas / cm³ | | --- | --- | --- | --- | | 12 | 10 | 10 | 5 | | 24 | 10 | 5 | 9 | | 36 | 20 | 4 | 28 |6 marks
  11. Name the part of a cell where aerobic respiration takes place.1 mark
  12. Describe aerobic respiration.2 marks
  13. A student says: "Aerobic respiration is breathing in oxygen and breathing out carbon dioxide." Write a correct description of aerobic respiration.2 marks
  14. A sprinter's muscle cells increase their rate of aerobic respiration at the start of a race. Explain why.2 marks
  15. State the word equation for aerobic respiration.2 marks
  16. Bacteria in a flask of nutrient solution respire aerobically. Name two substances the bacteria make.2 marks
  17. State the balanced chemical equation for aerobic respiration.2 marks
  18. Four molecules of glucose are respired aerobically. Calculate the number of molecules of carbon dioxide and of water that are made.2 marks
  19. Root cells of a rice plant respire aerobically. In a short time they make 54 molecules of water. (a) Calculate the number of molecules of glucose the cells break down. (b) Calculate the total number of molecules of reactants the cells use.4 marks
  20. A seal swims fast to catch a fish. A student writes three lines about the seal's muscle cells. Each line contains a mistake. Line 1: Aerobic respiration produces energy for muscle contraction. Line 2: The balanced chemical equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Line 3: 7 molecules of glucose need 6 molecules of oxygen and make 6 molecules of carbon dioxide. Correct each line.5 marks
  21. Describe anaerobic respiration.2 marks
  22. Compare the energy released per glucose molecule by anaerobic respiration with that released by aerobic respiration.1 mark
  23. Yeast is mixed with glucose solution and sealed from the air. State the word equation for the respiration that takes place.2 marks
  24. State the word equation for anaerobic respiration in muscles during vigorous exercise.2 marks
  25. The products alcohol, carbon dioxide and lactic acid can all come from anaerobic respiration. State which are made by yeast and which are made by muscle cells.3 marks
  26. A student says: 'Anaerobic respiration is when a cell stops respiring because it has no oxygen.' Correct the statement.3 marks
  27. A student writes C₆H₁₂O₆ → C₂H₅OH + CO₂ for anaerobic respiration in yeast. Explain why it is not balanced, and write the correct equation.3 marks
  28. After a sprint, an athlete's breathing stays deep and fast for several minutes. Explain why.3 marks
  29. Yeast cells in a sealed flask of glucose solution make 120 molecules of carbon dioxide by anaerobic respiration. (a) Write the balanced chemical equation. Use it to calculate the number of glucose molecules broken down and the number of ethanol molecules made. (b) Muscle cells break down the same number of glucose molecules by anaerobic respiration. State the number of carbon dioxide molecules they make. Give a reason. (c) The yeast cells then break down the same number of glucose molecules by aerobic respiration. State how the energy released compares.5 marks
  30. A rower's heart rate, breathing rate and blood lactic acid concentration are measured at rest and after a race. The results are in the table. (a) Explain why the lactic acid concentration is high at the end of the race. (b) A student writes: 'After the race, her heart rate and breathing rate increase to remove the lactic acid.' Use the data to correct the student. Explain what the heart rate and the breathing each do. (c) State where the lactic acid is broken down, and by which process. | time | heart rate / beats per minute | breathing rate / breaths per minute | lactic acid in blood / arbitrary units | | --- | --- | --- | --- | | at rest | 65 | 14 | 1 | | end of race | 185 | 48 | 10 | | 5 minutes after | 150 | 36 | 7 | | 30 minutes after | 68 | 15 | 1 |6 marks

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