Cover photo credits

From top left, in clockwise order:

Forest
San Juan Island forest, photographed by Tom Harpel, CC BY 2.0, via Wikimedia Commons

Cells
This image of cow lung cells is made from a Molecular Probes demo slide and is from the National Institutes of Health, Public domain, via Wikimedia Commons.
About the image:

• Cells: bovine pulmonary arthery endothelial cells
• Blue: nucleus stained with DAPI
• Green: Tubulin (microtubles) stained with antibody Bodipy FL goat anti-mouse IgG (Indirect fluorescent antibody stain)
• Red: F-Actin stained with Texas Red X-Phalloidin

Plant
Plant by Kurt Kaiser, CC0, via Wikimedia Commons

Protein composite
Relative size of different protein molecules, by Thomas Splettstoesser. Tamaño relativo de distintas moléculas proteicas, versión en español de Alejandro Porto., CC BY-SA 3.0, via Wikimedia Commons

Reef
Agincourt Reef, Great Barrier Reef, Queensland, Australia by Robert Linsdell, CC BY 2.0, via Wikimedia Commons

Giant Clam
Small Giant Clam (Tridacna maxima), Bango, Bunaken Island, Sulawesi, Indonesia by Bernard Dupont, CC BY-SA 2.0, via Wikimedia Commons