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Caffeine crystals

Annie Cavanagh and David McCarthy

Caffeine crystals

Download this image from Wellcome Collection.

This false-coloured scanning electron micrograph shows caffeine crystals. Caffeine is a bitter, crystalline xanthine alkaloid that acts as a stimulant drug. In plants, caffeine functions as a defence mechanism. Found in varying quantities in the seeds, leaves and fruit of some plants, caffeine acts as a natural pesticide that paralyses and kills certain insects feeding on the plant. The main crystals of caffeine were 400-500 microns long; however, this crystal group formed on the end of the larger crystal and measures around 40 microns in length.

What are the physiological effects of caffeine consumption?

Beverages containing caffeine - including coffee, tea, soft drinks and energy drinks - are extremely popular, and 90 per cent of adults consume caffeine daily. Caffeine acts as a metabolic stimulant on the central nervous system, reducing physical fatigue and drowsiness. Less than an hour after consumption, caffeine is reported to improve the flow of thought and increase focus and body coordination. However, the amount of caffeine required to produce these effects depends on a person's body size and degree of tolerance. The effects usually disappear after five hours. Too much caffeine can cause restlessness, nervousness, insomnia, nausea and vomiting, but normal levels of consumption (approximately 200-300 mg daily) pose few known health risks.

Why did the judges like this image?

James Cutmore, Picture Editor at BBC Focus Magazine, explains: "What interests me in my professional role is showing our readers images of everyday things from a different, at first unrecognisable, perspective. For that reason, this image really grabbed my attention. It's a bright, intricate image of something that most of us experience every day."