Coloured scanning electron micrograph (SEM) of a passion flower (Passiflora caerulea) pollen grain. Pollen grains are the male gametes (sex cells) of a plant. Magnification: when printed 10 centimetres wide.
Diatoms are microscopic algae composed of separate halves, with delicate siliceous cell walls. They're usually single-celled organisms, though some live colonially. They inhabit fresh and salt waters and are among the most abundant of all phytoplankton.
"This may look like Salvador Dali's Mae West Lips Sofa, but it is a colourised scanning electron microscope image of a diatom - a tiny single-celled marine creature invisible to the naked eye. Image by Dr Paul Hargreaves and Faye Darling