Single-celled phytoplankton carry out photosynthesis within specialized organelles called chloroplasts. Like factories, the chloroplasts' photosynthetic machinery requires raw materials and energy—sunlight—to operate. Cells living in the ocean must rapidly adapt to varying light levels caused by intermittent cloudy and bright conditions. (Illustration by Amy Caracappa-Qubeck and Katherine Joyce, Woods Hole Oceanographic Institution)[back]
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