Chloroplasts bear chlorophyll; they give the green world its color, and they carry out the business of photosynthesis. Around the inside perimeter of each gigantic cell trailed a continuous loop of these bright green dots. They spun . . . they pulsed, pressed, and thronged . . . they shone, they swarmed in ever-shifting files around and around the edge of the cell; they wandered, they charged, they milled, raced . . . they flowed and trooped greenly . . . All the green in the planted world consists of these whole, rounded chloroplasts . . . If you analyze a molecule of chlorophyll itself, what you get is one hundred thirty-six atoms of hydrogen, carbon, oxygen, and nitrogen arranged in an exact and complex relationship around a central ring. At the ring’s center is a single atom of magnesium. Now: If you remove the atom of magnesium and in its place put an atom of iron, you get a molecule of hemoglobin. The iron atom combines with all the other atoms to make red blood, the streaming red dots in the goldfish’s tail.
Annie Dillard, Pilgrim at Tinker Creek
animal, biochemistry, biology, chemistry, fact, know, lifeblood, nature, page-127-8, plant, science