Topic 7: Muscles and movement

Question 1

Explain one way in which cartilage at the ends of the bones in the knee joint reduces wear and tear (2)

Answer 1

-Compressible / cushioning to absorb shocks

-Smooth / slippery to reduce friction / prevent bones rubbing together

Question 2

Explain how the extensor and flexor muscles bring about movement of the lower leg (2)

Answer 2

-Tendons attach muscle to bone
-Flexor and extensor muscles act as an antagonistic muscle pair
-When the extensor muscles contract, it pulls on the tibia to extend the leg

Question 3

Function of ligaments

Answer 3

Connect bone to bone

Question 4

Function of cartilage

Answer 4

Act as a cushioning between bones

Question 5

Function of tendons

Answer 5

Connect muscle to bone

Question 6

Explain how the structure of a muscle fibre is related to its specialised function (3)

Answer 6

-Cell surface membrane contains voltage-gated channels to allow depolarisation of muscle fibre

-Many mitochondria for aerobic respiration

-Presence of myofibrils / actin and myosin

-Myofibrils allow contraction of muscle

Question 7

Describe two structural differences between fast twitch and slow twitch muscle fibres (2)

Answer 7

-Fast twitch muscle fibres have no / few mitochondria present. Slow twitch muscle fibres have many mitochondria

-Fast twitch muscle fibres have no / few capillaries present / slow twitch muscle fibres have many capillaries present

Question 8

Explain the advantages for long distance runners of having both fast and slow twitch muscle fibres, but not in equal quantities (5)

Answer 8

-Long duration activity so runners require muscle fibres that are slow to fatigue / fatigue resistant

-Low levels of anaerobic respiration reduces lactic acid build up

-ATP needed over a longer time frame so it is provided by more efficient process (aerobic respiration)

-High mitochondria for more aerobic respiration

-Fast twitch muscle fibres allows runner to run faster towards the end

Question 9

Describe how the concentration of calcium ions around that myofibrils is controlled (3)

Answer 9

-Calcium ions released from sarcoplasmic reticulum
-In response to action potentials / depolarisation / nerve impulse at neuromuscular junction
-Calcium channels open to allow calcium ions to cross the membrane
-Calcium ions taken back up into the sarcoplasmic reticulum by active transport

Question 10

Describe the role of calcium ions in the contraction of muscle fibres (3)

Answer 10

-Calcium ions bind to the troponin
-Causing tropomyosin to be displaced
-Exposing myosin to binding sites on actin

Question 11

Explain the effect of increasing calcium ion concentration on the mean force produced by muscle fibres (4)

Answer 11

-No force produced at low calcium ion concentration
-As calcium ion concentration increases force produced increases
-Because more actin and myosin interact / myosin exposed to binding sites
-No increase in force production at high calcium ion concentration
-As all actin and myosin are interacting / all myosin binding sites occupied

Question 12

The myosin binding site is found on

A) Actin
B) Sarcoplasmic reticulum
C) Tropomyosin
D) Troponin

Answer 12

A - Actin

Question 13

Compare and contrast the structure of an actin filament and collagen (3)

Answer 13

Differences:
-Only actin has a tertiary structure
-Collagen has three chains where as actin has one chain

Similarities:
-Both are made up of a base sequence of amino acids joined together by peptide bonds
-Both have a secondary structure

Question 14

The thick filament in a myofibril contains myosin. The myosin head contains the enzyme ATPase.
Explain the importance of the primary structure for the functioning of this enzyme (3)

Answer 14

-Primary structure determines interaction between amino acids / R groups
-Primary structure determines folding / tertiary structure
-Therefore affecting the shape of the active site
-Active site is complementary to ATP

Question 15

Cells produce lactate during anaerobic respiration. Lactate travels in the blood to the liver.
Liver cells can absorb lactate from the blood
Deduce what happens to the lactate in these cells (3)

Answer 15

-Lactate is oxidised to form pyruvate

-Pyruvate is converted to glucose

-Glucose is used in respiration

Question 16

Features of slow twitch muscle fibres

Answer 16

-Steady action for a maintained time period
-Endurance activity —> Slow contractions
-Have many mitochondria
-Aerobic respiration
-Rich blood supply and lots of myoglobin
-Rely on glucose as fuel and produce ATP because oxygen is available
-Have many capillaries to give good oxygen supply

Question 17

Features of fast twitch muscle fibres

Answer 17

-Fast contractions
-Anaerobic respiration
-Low levels of myoglobin
-Rich glycogen store
-More myofibrils than slow twitch fibres
-Creatine phosphate (used to form ATP)
-Fewer mitochondria than slow twitch

Question 18

Person A = 80% fast twitch, 20% slow twitch
Person B = 50% fast twitch, 50% slow twitch

Explain which person has muscles that are more resistant to fatigue (4)

Answer 18

-Person B has more slow twitch fibres than person A
-Slow twitch are more efficient at aerobic respiration because they have more mitochondria
-Slow twitch have many capillaries to give good oxygen supply
-Slow twitch have lots of myoglobin to store oxygen
-Therefore less likely to build up lactate

Question 19

Explain why muscles occur in antagonistic pairs (2)

Answer 19

-Muscles can only work in one direction
-Therefore there is a need to create opposite forces