![stylised 24 hour clock showing release and uptake of magnesium during the night and day](https://www2.mrc-lmb.cam.ac.uk/wordpress/wp-content/uploads/cover_nature-clock-magnesium-150x150.jpg)
Most organisms, including humans and plants, have circadian rhythms that allow them to adjust their metabolism and behaviour to match the 24-hour cycle of day and night. Circadian rhythms are even observed at the level of individual cells, and are dependent upon a biological clock mechanism that is not fully understood.