muscles

Question 1

name the 3 types of muscles

Answer 1

cardiac
smooth
skeletal

Question 2

what 2 protein filaments make up myofibrils

which is thicker and which is thinner

Answer 2

actin- thinner

myosin- thicker

Question 3

what are the names of the fibres making up the muscles

Answer 3

myofibrils

Question 4

name of cytoplasm in muscle cells

Answer 4

sarcoplasm

Question 5

why do myofibrils appear striped

Answer 5

they have alternating light and dark bands

Question 6

name of the light band

why is it light

Answer 6

I band (Isotropic)

light because thin and thick filaments dont overlap here

Question 7

name of dark band

why is it dark

Answer 7

A band (Anisotropic)

dark because thick and thin bands do overlap

Question 8

what is in centre of A band

Answer 8

H zone

Question 9

what is at centre of I band

Answer 9

Z line

Question 10

what is the sarcomere

Answer 10

the distance between 2 adjacent Z lines

Question 11

what happens to sarcomere when muscle contracts

Answer 11

sarcomere shortens, distance between Z lines decreases

Question 12

what are slow twitch muscle fibres and how are they built for endurance

Answer 12

contract slower than fast twitch

less powerful contractions but over large time period

Question 13

adaptations of slow twitch muscle fibres

Answer 13

• large myoglobin store (stores O2)
• lots of mitochondria (makes ATP)
• rich supply of blood vessels (provide O2 and glucose for respiration)

Question 14

what are fast twitch muscle fibres and how are they built for intense exercise

Answer 14

contract faster than slow twitch

more rapid and powerful contractions over short time period

Question 15

adaptations of fast twitch muscle fibres

Answer 15

• high glycogen concentration (converted to glucose)
• store of phosphocreatine- makes ATP from ADP and Pi
• high concentration of enzymes for anaerobic respiration (make ATP)
• more numerous and thicker myosin filaments (more powerful contraction)

Question 16

what is a neuromuscular junction

Answer 16

connects a motor neurone to a skeletal muscle fibre

Question 17

describe transmission across a neuromuscular junction

Answer 17

1. AP reaches end of motor neurone
2. synaptic vesicles fuse with pre synaptic neurone membrane
3. release acetylcholine- diffuses across cleft
4. acetylcholine binds to receptors on post synaptic membrane
5. open Na+ channels- influx of Na+
6. depolarisation of membrane
7. acetylcholinesterase breaks acetylcholine into acetyl and choline
8. diffuse back into PNS and recombined by ATP

Question 18

similarities between a cholinergic synapse and a neuromuscular junction

Answer 18

• use acetylcholine neurotransmitter- diffuses across cleft
• acetylcholinesterase breaks acetylcholine into acetyl and choline
• receptors on membrane that when acetylcholine binds, there is influx of Na+
• both use Na/K pump to repolarise axon

Question 19

differences between cholinergic synapse and neuromuscular junction

Answer 19

-NJ connects motor neurone to muscle, CS connects neurone to post synaptic membrane

-NJ only motor neurones, CS motor, sensory, intermediate

• NJ end of neural pathway, CS AP forms in post synaptic neurone
• NJ receptors on muscle, CS receptors on post synaptic membrane
• NJ only excitatory, CS both excitatory and inhibitory

Question 20

what pairs do skeletal muscles occur in

Answer 20

antagonistic pairs

Question 21

what is an antagonistic pair of muscles

Answer 21

2 muscles that contract in opposite directions

Question 22

what is the sliding filament mechanism

Answer 22

actin and myosin filaments slide past one another and bring about contraction of muscle

Question 23

effect of muscle contraction on:

I band
sarcomere
H zone
A band

Answer 23

• narrows I band
• shortens the sarcomere
• narrows the H zone
• no change to A band

Question 24

what determines the width of the A band

Answer 24

the length of myosin filaments- this does not change during muscle contraction and therefore there is no change to width of A band

Question 25

what 3 proteins are involved in muscle contraction

Answer 25

actin myosin tropomyosin

Question 26

3 stages of muscle contraction

Answer 26

stimulation contraction relaxation

Question 27

describe the events of muscle stimulation

Answer 27

1. AP reaches neuromuscular joint 2. causes calcium ion channels to open- calcium ions diffuse into synaptic knob 3. influx of calcium causes vesicles to fuse with pre synaptic membrane and release acetylcholine 4. acetylcholine diffuses across cleft and binds to receptors on membrane of muscle fibre- depolarises the membrane

Question 28

describe the events of muscle contraction

Answer 28

1. muscle membrane has T tubules (extensions of membrane) AP moves along T tubules throughout sarcoplasm 2. Ca2+ was actively transported into ER from sarcoplasm so sarcoplasm has low Ca2+ concentration 3. AP reaches ER, opens Ca2+ channels in ER so Ca2+ diffuse down a conc gradient from sarcoplasm to ER 4. tropomyosin molecules block binding sites on actin filaments- the Ca2+ cause tropomyosin to pull away from actin- frees the binding sites 5. ADP attached to myosin heads binds to actin filament, form cross bridge 6. angle of myosin head changes, pulls actin filament along, releases ADP molecule 7. ATP molecule now attaches to each myosin head, causes head to detach from actin 8. Ca2+ ions activate ATPase, hydrolyses ATP to ADP + Pi, gives energy for myosin to return to OG state. ATP attached to myosin is now ADP 9. myosin head with ADP attached reattaches to actin further along. process repeats

Question 29

describe the events of muscle relaxation

Answer 29

1. Ca2+ ions actively transported back into ER using energy from ATP hydrolysis 2. no Ca2+ to pull tropomyosin away from actin so tropomyosin blocks actin filaments again 3. myosin can't bind to actin so contraction ceases and muscle relaxes

Question 30

describe the role of phosphocreatine as a supply of energy in the muscles

Answer 30

- store of phosphate- allows ATP to form from ADP and Pi immediately - makes ATP which can directly provide the muscles with energy

Question 31

2 uses of energy in the muscles

Answer 31

- movement of myosin heads - reabsorption of Ca2+ ions into ER by active transport

Question 32

Describe the roles of calcium ions and ATP in the contraction of a myofibril (5)

Answer 32

1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum; 2. (Calcium ions) cause movement of tropomyosin (on actin); 3. exposure of the binding sites on the actin; 4. Myosin heads attach to binding sites on actin; 5. Hydrolysis of ATP (on myosin heads) causes myosin heads to bend; 6. (Bending) pulling actin molecules; 7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites).

Question 33

Describe the role of calcium ions and ATP in muscle contraction (5)

Answer 33

1. Ca2+ removes blocking molecules / uncovers binding site on actin; 2. correct references to Ca2+ binding to moving tropomyosin; 3. allows myosin heads to attach to actin filaments; 4. allows sliding of the actin and myosin filaments; 5. binding of ATP causes myosin head to detach (from actin); 6. (hydrolysis of) ATP releases energy; 7. which changes the configuration of the myosin head;

Question 34

2 b. scientists suggested that a decrease in the force of muscle contraction is caused by an increase in the concentration of inorganic phosphate, Pi, in muscle tissues. Their hypothesis is that an increase in the concentration of Pi prevents the release of calcium ions within muscle tissues. Explain how a decrease in the concentration of calcium ions within muscle tissues could cause a decrease in the force of muscle contraction. (3)

Answer 34

1. (Less/No) tropomyosin moved from binding site 2. (Fewer/No) actinomyosin bridges formed; Accept actin and myosin do not bind. 3. Myosin head does not move OR (Less/No) ATPase (activation);

Question 35

(c) In muscles, pyruvate is converted to lactate during prolonged exercise. Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration. (2)

Answer 35

1. Regenerates/produces NAD 2. (So) glycolysis continues; .

Question 36

3. (b) The scientists then compared the length of time that the control mice and the trained mice could carry out prolonged exercise. The trained mice were able to exercise for a longer time period than control mice. Explain why. (1)

Answer 36

1. (More aerobic respiration) produces more ATP; 2. Anaerobic respiration delayed; 3. Less or no lactate;

Question 37

4. d. explain role of glycogen in skeletal muscle (2)

Answer 37

1. As a store of glucose OR To be hydrolysed to glucose; 2. For respiration / to provide ATP;

Question 38

4. (e) During vigorous exercise, the pH of skeletal muscle tissue falls. This fall in pH leads to a reduction in the ability of calcium ions to stimulate muscle contraction. Suggest how.

Answer 38

1. Low pH changes shape of calcium ion receptors 2. Fewer calcium ions bind to tropomyosin; 3. Fewer tropomyosin molecules move away; 4. Fewer binding sites on actin revealed; 5. Fewer cross-bridges can form OR Fewer myosin heads can bind

Question 39

Q5. (a) Describe the roles of calcium ions and ATP in the contraction of a myofibril. (5)

Answer 39

1. Calcium ions diffuse into myofibrils from (sarcoplasmic) reticulum; 2. (Calcium ions) cause movement of tropomyosin (on actin); 3. (This movement causes) exposure of the binding sites on the actin; 4. 5. Myosin heads attach to binding sites on actin; Hydrolysis of ATP (on myosin heads) causes myosin heads to bend; 6. (Bending) pulling actin molecules; 7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites).

Question 40

Q6. (a) What is the role of ATP in myofibril contraction? (2)

Answer 40

1. (Reaction with ATP) breaks/allows binding of myosin to actin 2. Provides energy to move myosin head;

Question 41

(c) The mice that were not able to produce creatine were homozygous for a recessive allele of a gene. Mice that are heterozygous for this allele are able to produce forces similar to those of normal mice that are homozygous for the dominant allele of the same gene. Explain why the heterozygous mice can produce forces similar to those of normal mice. (2)

Answer 41

1. (Heterozygous) have one dominant/normal allele (for creatine production); 2. (This) leads to production of enough/normal amount of creatine;