Internal and external influences on sleep

The most reported error: asked to define an ultradian rhythm, candidates write over 24 hours or weekly/monthly. It is less than 24 hours — the ~90-minute sleep cycle. Ultra misleads: each cycle is short, so more fit into a day. Giving only an example ('the sleep cycle') is not a definition. Check: does it happen more than once a day? If so, ultradian.

A bodily-rhythm definition that omits natural has scored zero — as have rewording the question ('a rhythm the body has') and giving only an example ('the sleep-wake cycle'). Full answer: a natural biological cycle that repeats over a set period. Natural separates a rhythm from a habit: eating at six repeats but is imposed, not generated by the body.

A two-mark item on the hormone route needs both elements. 'The pineal gland controls sleep' names a gland but no mechanism; 'melatonin makes you sleepy' names a hormone but not its source — each is one mark at most. Two-mark answer: the pineal gland responds to light by releasing melatonin, and melatonin induces sleepiness and times the sleep-wake cycle.

Examiners record answers that bright lights trick the brain into thinking it is daytime. That describes a belief, not a biological process, so it earns no credit. Replace it: bright light at the eye suppresses melatonin release from the pineal gland, so sleepiness does not build at the usual time. Skipping the melatonin step misses what is assessed.

A recurring trap that also appears on this option. Asked for a benefit of sleep, do not write what goes wrong without it (tired, cannot concentrate). Those are disadvantages of sleep deprivation. A benefit describes the sleeper's gain — restored energy, growth and repair, memory consolidation. Read which way the question points before writing.

A two-mark 'describe' needs two unique points; the same reworded scores one. On describe the difference (circadian vs ultradian), two definitions side by side count as an implicit difference worth one — a connective (whereas) earns the second. Keep halves comparable: a length against a length ('24 hours whereas less than 24 hours'), not a length against an example.

Many think the clock is driven from outside — light in, melatonin out, sleep. The reverse is true: the rhythm is generated internally and keeps running with all cues removed, the key point. Light is a zeitgeber that resets the cycle, not creates it; remove light and it drifts past 24 hours, not stops. Melatonin is no sleeping drug: it only induces sleepiness.