A good marker of dietary intake of iodine is the urinary iodine level (UI). A study was carried out in the UK to establish urinary iodine levels and milk intake in schoolgirls aged 14–15 years.

Urinary iodine values from 50 to 99 μg dm^–3 are considered to be mild iodine deficiency. Deduce the effect of milk intake on the iodine status of schoolgirls in the UK.

Outline the need for iodine in the endocrine system.

Growth hormones are examples of peptide hormones. Explain the mechanism of action of peptide hormones.

a. the more milk taken in, the higher the iodine levels 

b. when no milk consumed all girls «in study» were iodine deficient 

c. in all cases median value is mildly deficient so milk may have no effect 

d. increase above 1 cup/day may have no/little effect

Accept answers in the converse.

a. iodine is absorbed/used/needed by the thyroid 

b. «needed» to synthesise thyroxin 

c. lack of iodine causes swelling of thyroid gland/goiter/hypothyroidism
OR
thyroxin used to regulate metabolic rate/generate heat

a. «peptide hormones» do not enter cells 

b. bind to «specific surface» receptors in plasma membrane 

c. leads to production /release of a secondary messenger inside cell 

d. triggers a cascade of reactions in the cytoplasm 

e. usually involves activating or inhibiting enzymes