Section B Answer one question.

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2019). The mark or mark type is shown in brackets.

1. [7] any seven from: 1 calcium ions released from sarcoplasmic reticulum ; 2 calcium ions bind to troponin; 3 troponin changes shape and moves tropomyosin; 4 exposes binding site on actin ; 5 myosin head, binds to site / forms cross bridge ; 6 myosin head tilts ; 7 pulls actin / power stroke; 8 myosin head, has ATPase / hydrolyses ATP ; 9 myosin head lets go of actin; 10 myosin head goes back to previous orientation / myosin head re-cocks ; 11 process repeated; 12 sarcomere shortens;
2. [8] any eight from: 1 FSH secreted by anterior pituitary ; 2 stimulates, development / growth, of follicle (cells in ovary) ; 3 dominant/Graafian, follicle, secretes oestrogen ; 4 oestrogen stimulates repair of endometrium; 5 oestrogen inhibits further release of FSH ; 6 (large) increase oestrogen, day 14/midpoint; 7 stimulates secretion of LH from anterior pituitary ; 8 LH stimulates, ovulation / release of oocyte; 9 LH stimulates development of corpus luteum ; 10 corpus luteum secretes progesterone ; 11 progesterone continues build-up of endometrium or maintains endometrium ; 12 progesterone, inhibits secretion of, LH/FSH ; 13 corpus luteum degenerates so concentration of progesterone falls ; 14 endometrium breaks down ;