Aerobic and anaerobic respiration
By the end of this chapter you will be able to
- Write the word and symbol equations for aerobic respiration
- Name the uses of the energy released by respiration
- Compare aerobic and anaerobic respiration, and explain oxygen debt
- Carry out and interpret the yeast practical, and calculate a rate of gas production
- [H] Compare the energy values of fats, carbohydrates and proteins, and link exercise to metabolic rate
You should already know
- Glucose and its role in photosynthesis (Chapter 9)
- Enzymes and temperature (Chapter 5)
- Mitochondria (Chapter 2)
Where this leads
- Muscle contraction and the nervous system (Chapter 11)
- Respiration and the heart (Chapter 6)
- Metabolic rate and hormones (Chapter 12)
GCSE Biology. Content follows the GCSE (9-1) subject content for England (Edexcel and AQA). Content references: Describe respiration as an exothermic reaction in every cell, and write the equations for aerobic respiration, Describe the uses of the energy released by respiration, Describe anaerobic respiration in muscles and in yeast, and oxygen debt, Investigate the effect of temperature on the rate of anaerobic respiration in yeast, using gas production, [H] Compare the energy values of food, and describe metabolic rate and exercise.
Exercise P Do you remember?
Method. Recall the organelle.
- Recall. Aerobic respiration takes place in the mitochondria.takes place in the mitochondria
- Write the answer. mitochondria
Check. Chloroplasts make glucose, not energy. ✓
Method. Recall the gas.
- Recall. Aerobic respiration uses oxygen.uses oxygen
- Write the answer. oxygen
Check. Carbon dioxide is breathed out. ✓
Method. Multiply the numbers in pairs.
- Multiply. 3 x 6 = 18, then 18 x 10 = 180.3 x 6 x 10 = 180
- Write the answer. 180
Check. 180 divided by 10 is 18. ✓
Method. Recall the sugar.
- Recall. Photosynthesis makes glucose.makes glucose
- Write the answer. glucose
Check. Glucose is a sugar used in respiration. ✓
Method. Recall the direction.
- Recall. Water moves from a dilute solution to a concentrated one by osmosis.dilute to concentrated
- Write the answer. from dilute to concentrated
Check. This is a passive movement. ✓
Respiration in every cell
Respiration is the process that releases energy from glucose. It is an exothermic reaction, meaning that it releases energy, some of which is given off as heat. It happens in every living cell, all the time. In aerobic respiration, glucose and oxygen react in the mitochondria to give carbon dioxide and water, and a large amount of energy is released.
Word equation: glucose + oxygen -> carbon dioxide + water (energy released).
Symbol equation: C6H12O6 + 6O2 -> 6CO2 + 6H2O (energy released).
Key ideas
- Respiration releases energy from glucose in every living cell.
- It is exothermic: energy is released, and some is given off as heat.
- Aerobic respiration uses oxygen and takes place in the mitochondria.
- Products of aerobic respiration: carbon dioxide and water.
Method. Name the reactants and the products.
- Reactants. The reactants are glucose and oxygen.glucose and oxygen
- Products. The products are carbon dioxide and water, with energy released.carbon dioxide and water
- Write it. Glucose + oxygen -> carbon dioxide + water.glucose + oxygen
- Write the answer. glucose + oxygen -> carbon dioxide + water
Check. Energy is released, not used up. ✓
Method. Recall the products.
- Recall. Aerobic respiration produces carbon dioxide and water.carbon dioxide and water
- Name them. The two products are carbon dioxide and water.carbon dioxide and water
- Write the answer. carbon dioxide and water
Check. Energy is also released. ✓
Method. Think about the energy change.
- Think. In an exothermic reaction, energy is transferred to the surroundings.transferred to the surroundings
- Conclude. So respiration releases energy, and some is given off as heat.given off as heat
- Write the answer. Respiration releases energy, and some of it is given off as heat to the surroundings.
Check. Exothermic means energy is released. ✓
Watch out
Watch out: respiration is not the same as breathing. Breathing moves air in and out; respiration is the chemical reaction in cells that releases energy.
Exam tip
Exam tip. Write the equations with the energy word included, so the marker can see that energy is released.
Try it (with your teacher). With your teacher, use a warm yeast and sugar mixture and a thermometer, and feel the warmth of the tube. Explain in one sentence why the tube gets warmer.
Exercise 10A Respiration in every cell
Method. Recall the starting substances.
- Recall. Aerobic respiration uses glucose and oxygen.glucose and oxygen
- Write the answer. glucose and oxygen
Check. Carbon dioxide and water are the products. ✓
Method. Recall the products.
- Recall. The products are carbon dioxide and water.carbon dioxide and water
- Write the answer. carbon dioxide and water
Check. Energy is also released. ✓
Method. Recall the organelle.
- Recall. Aerobic respiration takes place in the mitochondria.takes place in the mitochondria
- Write the answer. mitochondria
Check. Mitochondria are found in most cells. ✓
Method. Recall the energy change.
- Recall. Respiration releases energy, so it is exothermic.releases energy
- Write the answer. So yes.yes
- Write the answer. yes
Check. Exothermic reactions give out heat. ✓
Method. Recall where respiration happens.
- Recall. Respiration takes place in every living cell, all the time.every living cell
- Write the answer. every living cell
Check. It is not limited to muscles. ✓
Method. Check the atoms on each side.
- Glucose and oxygen. One glucose and six oxygen molecules are the reactants.C6H12O6 + 6O2
- Products. Six carbon dioxide and six water molecules are the products.6CO2 + 6H2O
- Write the answer. C6H12O6 + 6O2 -> 6CO2 + 6H2O
Check. Six carbon atoms on each side. ✓
Method. Read the symbol equation.
- Read. The equation has 6O2 on the left.6O2
- Write the answer. 6
Check. Six oxygen molecules for one glucose. ✓
Method. Recall the product.
- Recall. Carbon dioxide is a product of aerobic respiration, and it is breathed out.breathed out
- Write the answer. carbon dioxide
Check. Oxygen is breathed in. ✓
Method. Think about the energy released.
- Think. Respiration releases a lot of energy, and some is given off as heat.given off as heat
- Conclude. So the body feels warm during exercise.feels warm
- Write the answer. Accept any sentence that says respiration releases energy as heat.
Check. Exercise increases respiration. ✓
Method. Read the formula.
- Read. The formula C6H12O6 has 6 carbon atoms.6 carbon atoms
- Check. The 6CO2 on the right gives the same six carbon atoms.6CO2
- Write the answer. 6
Check. Carbon atoms balance in the equation. ✓
Method. Compare the two forms.
- Word. The word equation names the substances only.names the substances
- Symbol. The symbol equation shows the formulae and numbers of each molecule.numbers of each molecule
- Write the answer. Accept any sentence that says the symbol equation shows the numbers of molecules and atoms.
Check. The two equations describe the same reaction. ✓
Method. Link the need for energy to respiration.
- Need. Every cell uses energy for its processes all the time.uses energy
- Supply. Respiration releases the energy from glucose, in every cell.releases the energy
- Conclude. So respiration is needed in every living cell.every living cell
- Write the answer. Accept any answer that says every cell needs energy for its processes, and respiration releases that energy from glucose.
Check. Without respiration, the cell would stop working. ✓
Using the energy from respiration
The energy released by respiration is used in several ways. It is used to build up molecules, such as proteins from amino acids. It is used for muscle contraction, so that the muscles can move. It is used for active transport, moving substances against a concentration gradient. In mammals, some energy is used to keep the body warm.
| Use of energy | Example |
|---|---|
| building up molecules | making proteins from amino acids |
| muscle contraction | moving the arm when doing a press-up |
| active transport | absorbing mineral ions into root hair cells |
| keeping warm | maintaining the body temperature |
Key ideas
- Respiration releases energy for building molecules, muscle contraction, active transport and keeping warm.
- Muscles need a lot of energy during exercise.
- Active transport uses energy from respiration to move particles against the gradient.
- Building proteins from amino acids needs energy.
Method. Think about what a muscle does.
- Think. A muscle uses energy to contract and move the body.contract
- Name it. So the use is muscle contraction.muscle contraction
- Write the answer. muscle contraction
Check. The energy is used, not stored. ✓
Method. Recall the process against a gradient.
- Recall. Moving particles against a concentration gradient needs energy.needs energy
- Name it. This process is active transport.active transport
- Write the answer. active transport
Check. Diffusion needs no energy. ✓
Method. Think about what the cell builds.
- Think. Cells build large molecules, such as proteins, from smaller units.build proteins
- Name it. Building proteins from amino acids uses energy.building proteins
- Write the answer. building proteins from amino acids
Check. Energy is needed to join the units together. ✓
Watch out
Watch out: the energy from respiration is not stored in the molecules that are built. It is used to build them, and it is used up in the building.
Exam tip
Exam tip. When you name a use of energy, give the process and an example: “muscle contraction, for example moving the arm”.
Try it (with your teacher). With your teacher, do ten gentle squats and then feel your heart rate. Explain in one sentence which use of respiration energy the muscles are using.
Exercise 10B Using the energy from respiration
Method. Recall the use.
- Recall. Energy from respiration is used for muscle contraction.muscle contraction
- Write the answer. muscle contraction
Check. Muscles pull on bones. ✓
Method. Recall the use for building.
- Recall. Energy is used to build up molecules such as proteins.build up molecules
- Write the answer. building molecules
Check. Amino acids are joined to make proteins. ✓
Method. Recall the process.
- Recall. Active transport uses energy to move particles against a gradient.against a gradient
- Write the answer. active transport
Check. Diffusion does not use energy. ✓
Method. Recall the use for heat.
- Recall. Some of the energy from respiration is given off as heat, which keeps the body warm.given off as heat
- Write the answer. keeping the body warm
Check. The heat is a by-product of respiration. ✓
Method. Recall the use.
- Recall. Muscle contraction uses energy from respiration.uses energy from respiration
- Write the answer. So yes.yes
- Write the answer. yes
Check. Exercise increases the need for energy. ✓
Method. Recall an example.
- Recall. Root hair cells take in mineral ions from the soil by active transport.root hair cells
- Write the answer. mineral ions into root hair cells
Check. It needs energy from respiration. ✓
Method. Think about the muscles.
- Think. Exercise makes the muscles contract many times.contract many times
- Conclude. Each contraction needs energy, so more respiration is needed.more respiration
- Write the answer. Accept any sentence that says the muscles use more energy to contract during exercise.
Check. Exercise raises the rate of respiration. ✓
Method. Think about what stops.
- Think. If the muscles stopped moving, they would stop contracting.stop contracting
- Conclude. So muscle contraction would be the most reduced use.most reduced
- Write the answer. Accept muscle contraction.
Check. Other uses continue at rest. ✓
Method. Think about the direction of the ions.
- Think. Mineral ions are at a higher concentration in the root hair cell than in the soil.higher concentration
- Conclude. So moving them in is against the gradient, which needs energy.needs energy
- Write the answer. Accept any sentence that says active transport moves the ions against the gradient, which needs energy.
Check. Energy comes from aerobic respiration. ✓
Method. Think about where the energy goes.
- Used. Energy from respiration is used to join the amino acids together.used to join
- Not stored. The protein does not keep the energy as a store.does not keep
- Conclude. So the energy is used up in building the protein, not stored in it.used up
- Write the answer. Accept any answer that says the energy is used up in building the protein, not stored in it.
Check. Energy is transferred into the process, then used. ✓
Anaerobic respiration and oxygen debt
When there is not enough oxygen for aerobic respiration, muscles use anaerobic respiration. Glucose is converted to lactic acid, and only a small amount of energy is released. Lactic acid builds up and causes the muscles to tire.
Yeast also respires anaerobically, in a process called fermentation. Glucose is converted to ethanol and carbon dioxide. This is used in bread-making and brewing.
After exercise, the body needs extra oxygen to break down the lactic acid and to restore the body to its resting state. This extra oxygen is the oxygen debt. Breathing stays fast for a while after exercise.
| Feature | Aerobic | Anaerobic (muscles) | Anaerobic (yeast) |
|---|---|---|---|
| oxygen needed | yes | no | no |
| products | carbon dioxide and water | lactic acid | ethanol and carbon dioxide |
| energy released per glucose | a lot | a little | a little |
| where it happens | mitochondria | cytoplasm | cytoplasm |
Key ideas
- Anaerobic respiration in muscles: glucose to lactic acid.
- Anaerobic respiration in yeast: glucose to ethanol and carbon dioxide.
- Anaerobic respiration releases much less energy than aerobic respiration.
- Oxygen debt is the extra oxygen needed after exercise to clear lactic acid.
Method. Recall the product in muscles.
- Recall. In muscles, glucose is converted to lactic acid without oxygen.lactic acid
- Name it. So the product is lactic acid.lactic acid
- Write the answer. lactic acid
Check. Lactic acid causes muscle fatigue. ✓
Method. Recall the products of yeast.
- Recall. Yeast converts glucose to ethanol and carbon dioxide.ethanol and carbon dioxide
- Name them. The products are ethanol and carbon dioxide.ethanol and carbon dioxide
- Write the answer. ethanol and carbon dioxide
Check. Yeast does this in the absence of oxygen. ✓
Method. Think about the oxygen needed after exercise.
- Think. After exercise the body needs extra oxygen.extra oxygen
- Conclude. This extra oxygen clears lactic acid and restores the resting state.clears lactic acid
- Write the answer. Oxygen debt is the extra oxygen the body needs after exercise to clear lactic acid and restore the resting state.
Check. The debt is paid back by breathing harder. ✓
Watch out
Watch out: anaerobic respiration does not produce much energy. It is a short-term supply, and it is not a replacement for aerobic respiration.
Exam tip
Exam tip. Name the organism or tissue with its product: “muscles: lactic acid”, “yeast: ethanol and carbon dioxide”.
Try it (with your teacher). With your teacher, compare the breathing rate after a minute of gentle stepping and after a minute of brisk stepping. Describe the difference, and link it to oxygen debt.
Exercise 10C Anaerobic respiration and oxygen debt
Method. Recall the muscle product.
- Recall. Anaerobic respiration in muscles produces lactic acid.produces lactic acid
- Write the answer. lactic acid
Check. Lactic acid is a waste product. ✓
Method. Recall the yeast products.
- Recall. Yeast produces ethanol and carbon dioxide.ethanol and carbon dioxide
- Name it. The alcohol produced is ethanol.ethanol
- Write the answer. ethanol
Check. The carbon dioxide makes the bread rise. ✓
Method. Recall the gas.
- Recall. Yeast produces carbon dioxide along with ethanol.along with ethanol
- Write the answer. carbon dioxide
Check. Carbon dioxide is the gas that is measured in the practical. ✓
Method. Recall the condition.
- Recall. Anaerobic respiration takes place without oxygen.without oxygen
- Write the answer. So no.no
- Write the answer. no
Check. Aerobic respiration needs oxygen. ✓
Method. Recall the term.
- Recall. The extra oxygen needed after exercise is the oxygen debt.oxygen debt
- Write the answer. oxygen debt
Check. It clears lactic acid. ✓
Method. Link the debt to the breathing.
- Debt. The body needs extra oxygen to repay the oxygen debt.repay the oxygen debt
- Breathing. So breathing stays fast until the debt is paid.stays fast
- Write the answer. Accept any sentence that says the body must repay the oxygen debt, so breathing stays fast.
Check. Fast breathing supplies the extra oxygen. ✓
Method. Compare the products.
- Aerobic. Aerobic respiration gives carbon dioxide and water.carbon dioxide and water
- Anaerobic. Anaerobic respiration in muscles gives lactic acid; in yeast it gives ethanol.lactic acid or ethanol
- Write the answer. Accept lactic acid, or ethanol.
Check. Those products are not made in aerobic respiration. ✓
Method. Recall where anaerobic respiration happens.
- Recall. Anaerobic respiration happens in the cytoplasm, not the mitochondria.in the cytoplasm
- Write the answer. Accept cytoplasm.
Check. Mitochondria are used in aerobic respiration only. ✓
Method. Link the pain to the lactic acid.
- Cause. Without enough oxygen, the muscles make lactic acid by anaerobic respiration.make lactic acid
- Pain. The lactic acid builds up and causes the muscles to tire and burn.burn
- Write the answer. Accept any sentence that says lactic acid builds up in the muscles when there is not enough oxygen.
Check. Lactic acid is the cause of the tiredness. ✓
Method. Consider the energy and the waste product.
- Energy. Anaerobic respiration releases only a small amount of energy from each glucose.small amount of energy
- Waste. Lactic acid builds up, so the muscles tire and cannot keep working.cannot keep working
- Conclude. So the anaerobic supply is only for a short burst of effort.short burst
- Write the answer. Accept any answer that says it releases little energy per glucose, and the lactic acid build-up stops the muscles from working.
Check. Aerobic respiration is needed for long efforts. ✓
Required practical: yeast and temperature
In this practical the independent variable is the temperature of the yeast and sugar mixture, and the dependent variable is the volume of gas collected in 5 minutes. The gas is carbon dioxide, a product of anaerobic respiration (fermentation). The rate is found from the volume: rate = gas volume / time. The control variables are the mass of yeast, the concentration and volume of sugar solution, and the time.
Yeast is a safe, school-approved organism. The water bath is set by the teacher, and the apparatus is checked before use.
| Temperature (C) | Gas in 5 min (cm3) | Rate = gas / 5 (cm3 per min) |
|---|---|---|
| 20 | 5 | 1 |
| 30 | 15 | 3 |
| 40 | 25 | 5 |
| 50 | 10 | 2 |
Key ideas
- Independent variable: temperature. Dependent variable: volume of gas in 5 minutes.
- Rate = gas volume / time, so the rate is cm3 per minute.
- Keep the mass of yeast, the sugar solution and the time the same.
- The gas is carbon dioxide, produced by fermentation.
Method. Divide the gas volume by the time.
- Divide. Rate = 15 / 5.15 / 5
- Calculate. The rate is 3 cm3 per minute.15 / 5 = 3
- Write the answer. 3
Check. 3 x 5 = 15. ✓
Method. Find the highest rate in the table.
- Compare. The rates are 1, 3, 5 and 2 cm3 per minute.1, 3, 5, 2
- Read. The highest rate, 5 cm3 per minute, is at 40 degrees C.40
- Write the answer. 40
Check. The rate at 50 degrees C falls to 2. ✓
Method. Think about the enzymes in the yeast.
- Think. The enzymes in the yeast are denatured at 50 degrees C.denatured
- Conclude. So the rate of anaerobic respiration falls.rate falls
- Write the answer. At 50 degrees C the yeast enzymes denature, so the rate of anaerobic respiration falls.
Check. Denaturing is permanent. ✓
Watch out
Watch out: the gas is measured over a set time. Use the same time for each temperature, or the results cannot be compared.
Exam tip
Safety. Yeast is a safe organism, but do not taste the mixture. The water bath is controlled by the teacher, and the apparatus is kept stable.
Try it (with your teacher). With your teacher, set up yeast and sugar solution at two temperatures in gas-collecting tubes. Record the gas volume after 5 minutes, and calculate the rate for each.
Exercise 10D Required practical: yeast and temperature
Method. Find what is changed on purpose.
- Find it. The temperature of the yeast mixture is changed on purpose.changed on purpose
- Write the answer. temperature
Check. The gas volume is the dependent variable. ✓
Method. Find what is measured.
- Find it. The gas collected in 5 minutes is measured.gas collected
- Write the answer. volume of gas
Check. The gas is carbon dioxide. ✓
Method. Divide the volume by the time.
- Divide. Rate = 5 / 5 = 1.5 / 5 = 1
- Write the answer. 1
Check. 1 x 5 = 5. ✓
Method. Divide the volume by the time.
- Divide. Rate = 25 / 5 = 5.25 / 5 = 5
- Write the answer. 5
Check. 5 x 5 = 25. ✓
Method. Find the smallest gas volume in the table.
- Look. The volumes are 5, 15, 25 and 10 cm3.5, 15, 25, 10
- Compare. The smallest is 5 cm3, at 20 degrees C.5 cm3 at 20 degrees C
- Write the answer. 20
Check. The 10 cm3 at 50 degrees C is not the smallest. ✓
Method. Find the largest rate.
- Compare. The rates are 1, 3, 5 and 2.1, 3, 5, 2
- Read. The largest is 5, at 40 degrees C.40
- Write the answer. 40
Check. The rate at 30 degrees C is 3. ✓
Method. Think about the control variables.
- Think. More yeast would produce more gas, whatever the temperature.more gas
- Conclude. So the mass is a control variable, so only the temperature changes the result.only the temperature
- Write the answer. Accept any sentence that says the mass of yeast is a control variable, so only the temperature changes the result.
Check. Keep the other factors the same for a fair test. ✓
Method. Read the rates in order.
- Read. The rate rises from 1 at 20 degrees C to 5 at 40 degrees C.1 to 5
- Describe. So the rate rises as the temperature rises.rises
- Write the answer. Accept any sentence that says the rate rises as the temperature rises.
Check. Particles move faster and collide more often. ✓
Method. Find a weakness and its fix.
- Weakness. Only one tube may have been used at each temperature.one tube
- Fix. Repeat each temperature and take a mean, to make the rate more reliable.more reliable
- Write the answer. Accept any sensible improvement, such as repeating each temperature or testing a temperature closer to the best value.
Check. A named weakness needs a specific fix. ✓
Method. Link the gas to the reaction.
- Gas. Yeast produces carbon dioxide during anaerobic respiration.produces carbon dioxide
- Rate. So the volume of gas collected in a set time shows how fast the reaction is.how fast the reaction is
- Write the answer. Accept any answer that says the carbon dioxide is produced by anaerobic respiration, so more gas means a faster rate.
Check. The rate is the amount produced per minute. ✓
Energy in food and metabolic rate [H]
[H] Higher tier only. This section is higher-tier content. It uses approximate energy values per gram, for practice.
[H] Fats give the most energy per gram, about twice as much as carbohydrates or proteins. Metabolic rate is the rate at which the body uses energy. It rises during exercise, because the muscles use more energy, and it is also higher in people with more muscle mass.
| Food | Energy (kJ per gram, approximate) |
|---|---|
| carbohydrate | 16 |
| fat | 37 |
| protein | 17 |
Key ideas
- [H] Fat releases the most energy per gram.
- [H] Carbohydrate and protein release a similar energy per gram.
- [H] Energy released = mass of food x energy per gram.
- [H] Metabolic rate rises during exercise.
Method. Multiply the mass by the energy per gram.
- Multiply. Energy = 10 x 37.10 x 37
- Calculate. 10 x 37 = 370 kJ.370
- Write the answer. 370
Check. 370 divided by 10 is 37. ✓
Method. Divide the fat value by the carbohydrate value.
- Read. Fat gives 37 kJ per gram and carbohydrate gives 16 kJ per gram.37 and 16
- Divide. Divide 37 by 16 to compare them.37 / 16 = 2.3
- Write the answer. 2.3
Check. 16 x 2.3 is about 37. ✓
Method. Think about the muscles.
- Think. Muscles use more energy during exercise.more energy
- Conclude. So the rate at which the body uses energy rises.rate rises
- Write the answer. The muscles use more energy during exercise, so the metabolic rate rises.
Check. More respiration supplies the extra energy. ✓
Watch out
Watch out: the energy values are approximate and are for practice. Do not treat them as exact values for a particular food.
Exam tip
Exam tip. [H] Show the calculation: mass x energy per gram. Give the unit with the answer.
Try it (with your teacher). With your teacher, use a food label with energy and fat values. Work out the energy from 20 g of fat using the value on the label, and check it against the table.
Exercise 10E [H] Energy in food and metabolic rate
Method. Compare the values in the table.
- Compare. Fat gives 37 kJ per gram, more than carbohydrate (16) or protein (17).37 is the most
- Name it. So fat gives the most energy per gram.fat
- Write the answer. fat
Check. Fat is the most energy-dense food. ✓
Method. Read the table.
- Read. The table gives 16 kJ per gram for carbohydrate.16
- Write the answer. 16
Check. Protein is 17 kJ per gram. ✓
Method. Multiply the mass by the energy per gram.
- Multiply. 25 x 16 = 400.25 x 16 = 400
- Write the answer. 400
Check. 400 divided by 25 is 16. ✓
Method. Multiply the mass by the energy per gram.
- Multiply. 5 x 17 = 85.5 x 17 = 85
- Write the answer. 85
Check. 85 divided by 17 is 5. ✓
Method. Calculate both energies.
- Fat. 10 x 37 = 370 kJ.370 kJ
- Carbohydrate. 25 x 16 = 400 kJ.400 kJ
- Compare. So 25 g of carbohydrate gives more energy than 10 g of fat.25 g of carbohydrate
- Write the answer. 25 g of carbohydrate
Check. Compare the totals, not only the values per gram. ✓
Method. Think about the muscles.
- Think. Muscles use more energy during exercise.more energy
- Conclude. So the respiration rate rises to supply it.respiration rate rises
- Write the answer. Accept any sentence that says the muscles use more energy and so respiration rate rises.
Check. Breathing and heart rate also rise. ✓
Method. Compare the energy per gram.
- Value. Fat gives about 37 kJ per gram, the most of the three.37 kJ
- Store. So fat is an efficient energy store, which is why animals store it.efficient energy store
- Conclude. The student has the comparison the wrong way round.wrong way round
- Write the answer. Accept any answer that says fat gives the most energy per gram, so it is an efficient energy store.
Check. Fat gives more energy per gram than the other two. ✓
Chapter summary
| Skill | Method |
|---|---|
| Aerobic respiration | Glucose + oxygen -> carbon dioxide + water, with a lot of energy released in the mitochondria. |
| Uses of energy | Building molecules, muscle contraction, active transport and keeping warm. |
| Anaerobic in muscles | Glucose -> lactic acid, in the cytoplasm, with little energy released. |
| Anaerobic in yeast | Glucose -> ethanol and carbon dioxide (fermentation). |
| Oxygen debt | The extra oxygen needed after exercise to clear lactic acid. |
| Yeast practical | Rate = gas volume / time; temperature is the independent variable. |
| [H] Energy in food | Energy = mass x energy per gram; fat gives the most energy per gram. |
Can you…?
- I can write the word and symbol equations for aerobic respiration
- I can name the uses of the energy released by respiration
- I can compare aerobic and anaerobic respiration, and explain oxygen debt
- I can carry out the yeast practical and calculate a rate of gas production
- [H] I can compare the energy values of food and link exercise to metabolic rate
Key terms
- respiration
- the process that releases energy from glucose in every living cell
- exothermic
- a reaction that releases energy, some of it as heat
- aerobic respiration
- respiration using oxygen, which releases a lot of energy
- anaerobic respiration
- respiration without oxygen, which releases little energy
- lactic acid
- the product of anaerobic respiration in muscles
- fermentation
- anaerobic respiration in yeast, producing ethanol and carbon dioxide
- oxygen debt
- the extra oxygen needed after exercise to clear lactic acid
- metabolic rate
- the rate at which the body uses energy
- [H] energy per gram
- the energy released by one gram of a food
Exercise 10Z Check-up
Method. Recall the reactants and products.
- Recall. The reactants are glucose and oxygen; the products are carbon dioxide and water.reactants and products
- Write the answer. glucose + oxygen -> carbon dioxide + water
Check. Energy is released. ✓
Method. Recall the organelle.
- Recall. Aerobic respiration takes place in the mitochondria.takes place in the mitochondria
- Write the answer. mitochondria
Check. Mitochondria are in most cells. ✓
Method. Recall the product.
- Recall. Anaerobic respiration in muscles produces lactic acid.lactic acid
- Write the answer. lactic acid
Check. Yeast produces ethanol instead. ✓
Method. Recall the products.
- Recall. Yeast produces ethanol and carbon dioxide.ethanol and carbon dioxide
- Write the answer. ethanol and carbon dioxide
Check. Both are produced without oxygen. ✓
Method. Recall the term.
- Recall. The extra oxygen needed after exercise is the oxygen debt.oxygen debt
- Write the answer. oxygen debt
Check. It clears lactic acid. ✓
Method. Recall the uses.
- Recall. Respiration energy is used for muscle contraction, building molecules, active transport and keeping warm.four uses
- Choose one. Any one of these is correct.any one
- Write the answer. Accept any one: muscle contraction, building molecules, active transport, or keeping warm.
Check. Each use needs energy. ✓
Method. Divide the volume by the time.
- Divide. Rate = 15 / 5 = 3.15 / 5 = 3
- Write the answer. 3
Check. 3 x 5 = 15. ✓
Method. Recall the gas.
- Recall. The gas measured in the practical is carbon dioxide.carbon dioxide
- Write the answer. carbon dioxide
Check. Ethanol is a liquid. ✓
Method. Compare the completeness of the reaction.
- Think. In aerobic respiration glucose is fully broken down with oxygen.fully broken down
- Conclude. In anaerobic respiration it is only partly broken down, so less energy is released.partly broken down
- Write the answer. Accept any sentence that says glucose is not fully broken down, so less energy is released.
Check. Oxygen allows the complete breakdown. ✓
Method. Recall the process without oxygen.
- Recall. Respiration without oxygen is anaerobic respiration.without oxygen
- Write the answer. anaerobic respiration
Check. Aerobic respiration needs oxygen. ✓
Total 22 marks. Allow about 22 minutes.
Exercise 10X Exam-style questions
Method. Recall the reactants.
- Recall. The reactants are glucose and oxygen.glucose and oxygen
- Write the answer. glucose and oxygen
Check. Carbon dioxide and water are the products. ✓
Method. Recall the product.
- Recall. Anaerobic respiration in muscles produces lactic acid.lactic acid
- Write the answer. lactic acid
Check. Yeast gives ethanol. ✓
Method. Recall the process.
- Recall. Yeast respires without oxygen by fermentation.by fermentation
- Write the answer. fermentation
Check. Fermentation is anaerobic respiration in yeast. ✓
Method. Balance the atoms on each side.
- Reactants. Glucose and six oxygen molecules are on the left.C6H12O6 + 6O2
- Products. Six carbon dioxide and six water molecules are on the right.6CO2 + 6H2O
- Write the answer. C6H12O6 + 6O2 -> 6CO2 + 6H2O
Check. Count each atom on both sides. ✓
Method. Link the faster breathing to the oxygen debt.
- Debt. During the run, the muscles made lactic acid without enough oxygen.without enough oxygen
- Repay. After the run, extra oxygen is needed to clear the lactic acid, so breathing stays fast.clear the lactic acid
- Write the answer. Accept any answer that says the oxygen debt must be repaid, and lactic acid is cleared.
Check. Fast breathing supplies the extra oxygen. ✓
Method. Give three uses.
- Use 1. Muscle contraction uses the energy to move the body.muscle contraction
- Use 2. Building molecules, such as proteins, uses the energy.building molecules
- Use 3. Active transport uses it to move particles against a gradient.active transport
- Write the answer. Accept any three of: muscle contraction, building molecules, active transport, keeping warm.
Check. Keeping warm is another use. ✓
Method. Calculate, then explain the drop.
- Rate. The rate at 40 degrees C is 25 / 5 = 5 cm3 per minute.25 / 5 = 5
- Drop. At 50 degrees C the rate falls to 2 cm3 per minute.2 cm3 per minute
- Reason. The yeast enzymes denature at 50 degrees C, so the rate of respiration falls.denature
- Write the answer. Accept 5 cm3 per minute, with the denaturing of the enzymes explained.
Check. The best temperature is below the level that denatures. ✓
Method. Compare the products and the energy.
- Aerobic. Aerobic respiration gives carbon dioxide and water, and releases a lot of energy.a lot of energy
- Anaerobic. Anaerobic respiration in muscles gives lactic acid, and releases little energy.little energy
- Write the answer. Accept any answer that says aerobic respiration gives carbon dioxide and water and releases a lot of energy, while anaerobic gives lactic acid and releases little energy.
Check. Compare the products and the energy released. ✓
Method. Explain the energy change.
- Release. Respiration releases energy, so it is exothermic.releases energy
- Use. Some of the energy is used for other processes, and some is given off as heat.given off as heat
- Write the answer. Accept any answer that says the reaction releases energy, and some is given off as heat to the surroundings.
Check. Heat is the form lost to the surroundings. ✓
Method. Build the explanation in three parts.
- Build-up. During exercise, muscles respire anaerobically and lactic acid builds up.lactic acid builds up
- Debt. After exercise, extra oxygen is needed to clear the lactic acid.extra oxygen
- Breathing. So breathing stays fast until the oxygen debt is paid.stays fast
- Write the answer. Accept any answer that says lactic acid builds up during anaerobic respiration, the body needs extra oxygen to clear it, and breathing stays fast until the debt is paid.
Check. Each sentence builds on the one before. ✓