Floating kelp with many pneumatocysts

In phytology, a pneumatocyst is a large float containing gas found in brown algae. An organism may have more than one. They provide buoyancy to lift the blades toward the surface, allowing them to receive more sunlight for photosynthesis.

The proportion of gases in the pneumatocysts adjusts by equilibrating with the surrounding air or water. The pneumatocyst can hold O₂, CO₂ and CO.

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