Describe the process of spermatogenesis leading to the production of four sperm cells in a human male.

Outline the roles of estrogen and progesterone in females during human reproduction.

Explain the process of muscle contraction.

a. in the seminiferous tubule 

b. diploid cells/spermatogonia grow/enlarge 

c. two divisions of meiosis 

d. primary spermatocyte carries out the first division and secondary spermatocytes carry out the second division 

e. meiosis produces haploid cells/spermatids 

f. haploid cells/spermatids differentiate into spermatozoa/sperm cells
OR
develop tail/flagellum/helical mitochondrion/acrosome/sac of enzymes 

g. Sertoli cells help sperm to mature/differentiate

Allow answers presented in a clearly annotated diagram.

a. estrogen/progesterone for repair/thickening/development/vascularisation of uterus lining/endometrium 

b. estrogen (at high levels) stimulates LH secretion (which stimulates ovulation)

c. progesterone maintains the uterus lining/endometrium during pregnancy/prevents miscarriage 

d. progesterone/estrogen inhibits FSH/LH secretion 

e. progesterone for development of breast tissue during pregnancy 

f. fall in progesterone/rise in estrogen leads to labour/contractions/childbirth 

g. estrogen/progesterone cause pre-natal development of female reproductive organs
OR 
h. estrogen/progesterone cause secondary sexual characteristics

a. muscle fibre contains many myofibrils 

b. made up of sarcomeres/labelled diagram showing one or more sarcomeres 

c. nerve impulse/signal from (motor) neuron causes release of calcium (ions)/Ca²⁺ 

d. calcium (ions)/Ca²⁺ released from sarcoplasmic reticulum 

e. calcium (ions)/Ca²⁺ link to troponin 

f. tropomyosin moves to expose actin binding sites 

g. ATP hydrolysis/ATP to ADP and phosphate/release of phosphate from ATP 

h. ATP binds to myosin heads and causes them to cock/change angle/release/gain energy 

i. myosin heads bind/form cross-bridges to actin 

j. myosin heads push on actin and then detach from actin 

k. actin moved towards centre of sarcomere/sliding of filaments 

l. sarcomere becomes shorter (resulting in muscle contraction)

Accept any mark point if clearly made on an annotated diagram.