Key for AQA Biology B9 [ Teacher ]

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B9 Respiration
Student Book answers
B9.1 Aerobic respiration
Question
number
Answer Marks Guidance
1 a glucose + oxygen → carbon dioxide + water (energy transferred to
environment)
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1 b C6H12O6 + 6O2 → 6CO2 + 6H2O (energy transferred to environment) 2
1 c Muscle cells are very active and need a lot of energy.
They need large numbers of mitochondria to supply energy as aerobic
respiration takes place in mitochondria.
Fat cells use very little energy
so need very few mitochondria.
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2 a movement,
building new molecules,
heat generation
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2 b People become thin because stored energy is used up
and growth stops as new proteins are not made for lack of energy and
raw materials.
People lack energy for movement as there is insufficient fuel for
respiration in mitochondria.
People feel cold as there is insufficient fuel for respiration in
mitochondria, which transfers energy to the body to warm it up.
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3 Accept any appropriate suggestion for practical investigation. 6

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B9 Respiration
Student Book answers
B9.2 The response to exercise
Question
number
Answer Marks Guidance
1 a i Increases before exercise starts as a result of anticipation, rises rapidly
as exercise begins, followed by steady rise and then sharp fall as
exercise finishes.
Increased heart rate supplies muscles with extra blood needed to bring
glucose and oxygen to muscle fibres
and to remove increased amounts of carbon dioxide.
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1 a ii Increases more slowly and evenly than heart rate but remains high for
some time after exercise.
Increased heart rate supplies enough oxygen initially, then breathing
rate needs to increase to meet demand.
When exercise stops, breathing rate remains high until oxygen debt
paid off.
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1 b Unfit person has lower heart volume at rest than fit person
and is not able to pump as much blood out of heart during each beat at
rest as fit person is.
This means unfit person’s heart has to work harder to deliver same
volume of blood to muscle cells and remove waste.
Heart rate will therefore be faster in unfit person than fit person.
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2 a complex carbohydrate
stored in muscles
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2 b Glycogen can be converted rapidly into glucose
to provide fuel for aerobic respiration, providing body cells with energy.
Muscle tissue often needs sudden supply of energy for rapid contraction
in a way that most other tissues do not,
so muscle needs a glycogen store.
Other tissues don’t need energy in the same way so have not evolved
to have glycogen stores.
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B9 Respiration
Student Book answers
3 a Award marks based on ideas presented and method produced.
Look for sensible ideas, safe investigation, clear instructions, realistic
expectations, appropriate methods of recording and analysis,
awareness of weakness in investigation, and understanding of
variables.
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3 b Results will depend on method chosen and fitness parameter
investigated. Look for awareness that fitness will vary (can be affected
by age, lifestyle, or health issues).
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B9 Respiration
Student Book answers
B9.3 Anaerobic respiration
Question
number
Answer Marks Guidance
1 After long period of exercise muscles become short of oxygen and
switch from aerobic to anaerobic respiration, which is less efficient.
Glucose molecules are not broken down completely,
so less energy is released than during aerobic respiration.
End products of anaerobic respiration are lactic acid and a small
amount of energy, resulting in muscle fatigue.
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2 a cellular respiration without oxygen 1
2 b animals:
 anaerobic respiration takes place in muscles when not enough
oxygen, produces lactic acid
 and relatively small amount of energy,
 allows animal to continue running even when they cannot
breathe fast enough to supply the oxygen they need
plants and yeast:
 anaerobic respiration forms ethanol and carbon dioxide,
 allows plant/yeast to continue to respire in low‑oxygen
atmospheres,
 rare in plants as they form oxygen during photosynthesis but
more common in yeasts, where fermentation is used in baking
and brewing
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2 c animals: glucose → lactic acid (energy transferred to environment)
plants and yeast: glucose → ethanol + carbon dioxide (energy
transferred to environment)
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3 Lactic acid produced during exercise as a result of anaerobic respiration
has to be converted back into glucose.
This needs oxygen, and the amount of oxygen needed for this process
is known as oxygen debt.
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B9 Respiration
Student Book answers
Even though muscles have stopped working, heart rate and breathing
rate stay high
to supply extra oxygen until all lactic acid is removed and oxygen debt
is paid off.
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B9.4 Metabolism and the liver
Question
number
Answer Marks Guidance
1 sum of all the reactions in a cell or in the body 1
2 Any four from:
 conversion of glucose to starch, glycogen, and cellulose
 formation of lipid molecules from a molecule of glycerol and
three fatty acid molecules
 use of glucose and nitrate ions to form amino acids used to
make proteins
 respiration
 photosynthesis
 breakdown of excess proteins to form urea
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3 Liver is involved in a number of processes requiring a lot of energy,
including removal of lactic acid produced during anaerobic respiration
(blood carries lactic acid from muscles to liver, where it is converted
back to glucose for aerobic respiration in cells),
conversion of glucose to glycogen when in excess,
and conversion of glycogen back to glucose when needed for
respiration.
Liver consequently carries out a lot of aerobic respiration to provide
energy needed for these reactions.
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