Topic 7: Specification essay A*
1 Demonstrate knowledge and understanding of the How Science Works areas
listed in the table on page 13 of this specification.
2 Describe the structure of a muscle fibre and explain the structural and
physiological differences between fast and slow twitch muscle fibres.
A muscle fibre is made up of bundles of myofibrils and contain several nuclei. Each
myofibril consists of filaments: Actin (thin filament) and Myosin (thick filament). The
cell surface membrane of a muscle fibre is called the sarcolemma. The specialised
endoplasmic reticulum of a muscle fibre is called the sarcoplasmic reticulum (this
releases calcium ions in order for muscles to contract). The cytoplasm of a muscle cell
is called the sarcoplasm. The specialised synapse between neurones and muscle cells is
called the neuromuscular junction.
Slow twitch muscle fibres Fast twitch muscle fibres
Contain lots of mitochondria where lots Contains few mitochondria as not much
of ATP is produced energy is used
Is used for slower, sustained periods of Is used for short bursts of exercise
exercise
Carries out aerobic respiration Carries out anaerobic respiration
Lots of myoglobin to store oxygen Little myoglobin as less oxygen is used
Fatigue resistant Fatigue quickly
3 Explain the contraction of skeletal muscle in terms of the sliding filament
theory, including the role of actin, myosin, troponin, tropomyosin, calcium ions
(Ca2+), ATP and ATPase
1. The sarcolemma receives an electrical impulse which travels down the T-tubules
to the sarcoplasmic reticulum
2. The sarcoplasmic reticulum released calcium ions which bind to the Troponin
molecules
3. This causes the Troponin to change shape which causes the Tropomysin
molecules to unblock the actin-myosin binding site
4. The myosin head binds to the Actin-Myosin binding site on the Actin filament
and the hydrolysis of ATP into ADP + Pi releases energy for the myosin head to
change shape
5. This pulls the Actin filament along causing the sarcomere to shorten
6. Free ATP then binds to the myosin head causing the cross-bridge to break and
the myosin head detaches from the Actin filament, reattaches to another
binding site further down the filament and pulls it along further
7. This continues until calcium ions stop being released from the sarcoplasmic
reticulum and existing calcium ions travel back into the sarcoplasmic reticulum
by active transport using ATP
, 4 Recall the way in which muscles, tendons, the skeleton and ligaments interact to
enable movement, including antagonistic muscle pairs, extensors and flexors.
Tendons are non-elastic fibrous tissue that join muscles to the skeleton (bones).
Ligaments are elastic connective tissue that join bones to bones.
Skeletal muscles are those which are attached to bones and normally arranged in
antagonistic pairs (pairs of muscles that pull in opposite directions).
Antagonistic pairs are made up of flexors and extensors: Flexors are muscles which
contract to bend a joint whilst extensors are muscles which contract to straighten a
joint.
5 Describe the overall reaction of aerobic respiration as splitting of the
respiratory substrate (eg glucose) to release carbon dioxide as a waste product
and reuniting of hydrogen with atmospheric oxygen with the release of a large
amount of energy.
Glucose + Oxygen = Carbon dioxide + water + energy
6 Describe how to investigate rate of respiration practically.
1. Set up a respirometer and place equal volumes of potassium hydroxide into the
two test tubes on either side- these will absorb the carbon dioxide that is
produced
2. Place small organisms onto a piece of gauze over one of the test tubes above the
potassium hydroxide
3. Place a coloured fluid into the manometer tube
4. The rate is respiration is measured by observing the movement of the fluid in
the manometer towards the organism- the volume of oxygen absorbed can then
be calculated from this
5. Repeat the experiment and calculate a mean average to make the results more
reliable
7 Recall how phosphorylation of ADP requires energy and how hydrolysis of ATP
provides an accessible supply of energy for biological processes.
8 Describe the roles of glycolysis in aerobic and anaerobic respiration, including
the phosphorylation of hexoses, the production of ATP, reduced coenzyme and
pyruvate acid (details of intermediate stages and compounds are not required).
Glycolysis:
1. Glucose is taken from its storage molecule glycogen
1 Demonstrate knowledge and understanding of the How Science Works areas
listed in the table on page 13 of this specification.
2 Describe the structure of a muscle fibre and explain the structural and
physiological differences between fast and slow twitch muscle fibres.
A muscle fibre is made up of bundles of myofibrils and contain several nuclei. Each
myofibril consists of filaments: Actin (thin filament) and Myosin (thick filament). The
cell surface membrane of a muscle fibre is called the sarcolemma. The specialised
endoplasmic reticulum of a muscle fibre is called the sarcoplasmic reticulum (this
releases calcium ions in order for muscles to contract). The cytoplasm of a muscle cell
is called the sarcoplasm. The specialised synapse between neurones and muscle cells is
called the neuromuscular junction.
Slow twitch muscle fibres Fast twitch muscle fibres
Contain lots of mitochondria where lots Contains few mitochondria as not much
of ATP is produced energy is used
Is used for slower, sustained periods of Is used for short bursts of exercise
exercise
Carries out aerobic respiration Carries out anaerobic respiration
Lots of myoglobin to store oxygen Little myoglobin as less oxygen is used
Fatigue resistant Fatigue quickly
3 Explain the contraction of skeletal muscle in terms of the sliding filament
theory, including the role of actin, myosin, troponin, tropomyosin, calcium ions
(Ca2+), ATP and ATPase
1. The sarcolemma receives an electrical impulse which travels down the T-tubules
to the sarcoplasmic reticulum
2. The sarcoplasmic reticulum released calcium ions which bind to the Troponin
molecules
3. This causes the Troponin to change shape which causes the Tropomysin
molecules to unblock the actin-myosin binding site
4. The myosin head binds to the Actin-Myosin binding site on the Actin filament
and the hydrolysis of ATP into ADP + Pi releases energy for the myosin head to
change shape
5. This pulls the Actin filament along causing the sarcomere to shorten
6. Free ATP then binds to the myosin head causing the cross-bridge to break and
the myosin head detaches from the Actin filament, reattaches to another
binding site further down the filament and pulls it along further
7. This continues until calcium ions stop being released from the sarcoplasmic
reticulum and existing calcium ions travel back into the sarcoplasmic reticulum
by active transport using ATP
, 4 Recall the way in which muscles, tendons, the skeleton and ligaments interact to
enable movement, including antagonistic muscle pairs, extensors and flexors.
Tendons are non-elastic fibrous tissue that join muscles to the skeleton (bones).
Ligaments are elastic connective tissue that join bones to bones.
Skeletal muscles are those which are attached to bones and normally arranged in
antagonistic pairs (pairs of muscles that pull in opposite directions).
Antagonistic pairs are made up of flexors and extensors: Flexors are muscles which
contract to bend a joint whilst extensors are muscles which contract to straighten a
joint.
5 Describe the overall reaction of aerobic respiration as splitting of the
respiratory substrate (eg glucose) to release carbon dioxide as a waste product
and reuniting of hydrogen with atmospheric oxygen with the release of a large
amount of energy.
Glucose + Oxygen = Carbon dioxide + water + energy
6 Describe how to investigate rate of respiration practically.
1. Set up a respirometer and place equal volumes of potassium hydroxide into the
two test tubes on either side- these will absorb the carbon dioxide that is
produced
2. Place small organisms onto a piece of gauze over one of the test tubes above the
potassium hydroxide
3. Place a coloured fluid into the manometer tube
4. The rate is respiration is measured by observing the movement of the fluid in
the manometer towards the organism- the volume of oxygen absorbed can then
be calculated from this
5. Repeat the experiment and calculate a mean average to make the results more
reliable
7 Recall how phosphorylation of ADP requires energy and how hydrolysis of ATP
provides an accessible supply of energy for biological processes.
8 Describe the roles of glycolysis in aerobic and anaerobic respiration, including
the phosphorylation of hexoses, the production of ATP, reduced coenzyme and
pyruvate acid (details of intermediate stages and compounds are not required).
Glycolysis:
1. Glucose is taken from its storage molecule glycogen
