Relevant LO’s…
B2.6 Aerobic and anaerobic respiration
B2.6.1 Aerobic Respiration
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The chemical reactions inside cells are controlled by enzymes
During aerobic respiration (respiration that uses oxygen) chemical reactions occur that:
Use glucose (a sugar) and oxygen
Release energy
Aerobic respiration takes place continuously in both plants and animals
Most of the reactions in aerobic respiration take place inside mitochondria
Aerobic respiration is summarised by the equation:
Glucose + oxygen -> carbon dioxide + water (+ energy)
Energy that is released during respiration is used by the organism. The energy may be used:
To build larger molecules from smaller ones
In animals, to enable muscles to contract
In mammals and birds, to maintain a steady body temperature in colder surroundings
In plants, to build up sugars, nitrates and other nutrients into amino acids which are then built up into proteins
During exercise a number of changes take place:
The heart rate increases
The rate and depth of breathing increases
These changes increase the blood flow to the muscles and so increase the supply of sugar
and oxygen and increase the rate of removal of carbon dioxide
Muscles store glucose as glycogen, which can then be converted back to glucose for use
during exercise
Relevant LO’s
B2.6.2 Anaerobic Respiration
• During exercise, if insufficient oxygen is reaching the muscles they use anaerobic
respiration to obtain energy
• Anaerobic respiration is the incomplete breakdown of glucose and produces lactic acid
• **As the breakdown of glucose is incomplete, much less energy is released than
during aerobic respiration. Anaerobic respiration results in an oxygen debt that
must be repaid in order to oxidise lactic acid to carbon dioxide and water** (HT
only)
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If muscles are subjected to long periods of vigorous activity, they become fatigued
and stop contracting efficiently. One cause of muscle fatigue is the build up of lactic
acid in the muscles. Blood flowing through the muscles removes the lactic acid
Short Answer Questions
1. Respiration is a chemical process.
a) Where does respiration take place? Circle the correct answer.
chloroplasts
mitochondria
nuclei
ribosomes
(1)
b) Which food material is used in respiration?
_________________________________________________________________ (1)
c) Name the two waste materials that are produced in respiration.
_________________________________________________________________ (2)
d) Respiration is important in muscle contraction. Explain why.
_________________________________________________________________ (2)
2. a) Copy and complete the word equation for aerobic respiration.
Oxygen + __________ -> Water + __________ (+ energy)
b) i) Which substance is missing in anaerobic respiration?
_________________________________________________________________ (1)
ii) What is made during anaerobic respiration?
_________________________________________________________________ (1)
iii) Muscles get tired during anaerobic respiration. Explain why.
_________________________________________________________________ (1)
Past Paper Question – Longer Answer
In this question, you will be assessed on using good English, organising
information clearly and using specialist terms where appropriate
Rate at which muscles
produce carbon dioxide
(average)
Rate at which muscles
transfer energy (average)
The bar charts show what happens in an athlete’s muscles when running in
two races of different distances.
The equations show two processes
that occur in muscle cells.
Aerobic Respiration
Glucose + Oxygen -> Carbon Dioxide + Water
100m race
1500m race
Anaerobic Respiration
Glucose -> Lactic Acid
Use all the information to explain
what happens in the athlete’s
muscles when running in the two
races
(6)
Use all the information to explain what happens in the athlete’s muscles
when running in the two races
(6 marks)
5-6 marks
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There is a clear, balanced and
detailed explanation about
the differences between the
two races in terms of aerobic
and anaerobic respiration
The answer is coherent and in
a logical sequence
It contains a range of
appropriate or relevant
specialist terms used
accurately
The answer shows few errors
in spelling, punctuation and
grammar
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3-4 marks
1-2 marks
• There is some attempt to
explain the differences
between the two races in
terms of respiration
• The answer has some
structure and organisation
• The use of specialist terms has
been attempted, but not
always accurately
• There may be some errors in
punctuation, spelling and
grammar
• There is a brief description of
the differences between the
two races, which has little
clarity and detail
• The answer is poorly
constructed with an absence
of specialist terms or their use
demonstrates a lack of
understanding of their
meaning
• The spelling, punctuation and
grammar are weak
Examples of biology points made in the response:
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Energy is transferred faster in the 100m race
Carbon dioxide produced faster during the 1500m race/more
Carbon dioxide produced
Correct reference to twice/half as fast in either/both cases
Respiration during 100m race (mainly) anaerobic
Respiration during 1500m race (mainly) aerobic
Aerobic respiration produced carbon dioxide
Anaerobic respiration produced lactic acid
0 marks
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