A-LevelBiologyControl and coordination9700/43 · May/June 2018 · Q813 Marks
Striated muscle is made of many fibres. Each fibre is composed of myofibrils. The striated appearance of the muscle fibre is due to the arrangement of two types of protein filaments, thick filaments and thin filaments, within the sarcomeres of the myofibril. Describe the main structural features of thick filaments and thin filaments in the sarcomere. thick filaments ...................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... thin filaments ......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
- (a)Striated muscle is made of many fibres. Each fibre is composed of myofibrils. The striated appearance of the muscle fibre is due to the arrangement of two types of protein filaments, thick filaments and thin filaments, within the sarcomeres of the myofibril. Describe the main structural features of thick filaments and thin filaments in the sarcomere. thick filaments ...................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... thin filaments ......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................[4]
- (b)Describe the role of calcium ions in the contraction of striated muscle.[5]
- (c)Muscle cells sometimes have to carry out respiration in anaerobic conditions. Describe how respiration occurs in anaerobic conditions in a muscle cell and state why it is important that this process occurs.[4]
Mark scheme
Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.
- 8(a) four from:
- thick filaments (max 3)
- 1 myosin;
- 2 fibrous protein;
- 3 globular heads / ATPase ;
- 4 AVP; e.g. 15 nm diameter / M lines
- thin filaments (max 3)
- 5 actin;
- 6 globular protein ;
- 7 tropomyosin / troponin;
- 8 binding site for myosin (head) ;
- 9 AVP; e.g. 7 nm diameter / Z lines
- 8(b) five from:
- 1 (when) sarcoplasmic reticulum depolarised ;
- 2 calcium (ion) channels open ;
- 3 calcium ions, move in (sarcoplasm);
- 4 bind to troponin ;
- 5 troponin / tropomyosin, changes shape ;
- 6 moves tropomyosin out of the way / exposes (actin-myosin) binding sites ;
- 7 (allows) myosin to bind (to actin) / cross bridge formation;
- 8(c) four from:
- description
- 1 (pyruvate) accepts hydrogen / becomes reduced ;
- 2 from reduced NAD ;
- 3 produce lactate;
- 4 ref. to lactate dehydrogenase ;
- importance
- 5 glycolysis can continue ;
- 6 ref. to small amount of ATP produced ;
- 7 AVP; e.g. cannot continue for long / reversible / pyruvate does not enter mitochondrion
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