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Answer: Phytoplankton are microscopic organisms, mostly marine algae, that live in watery environments both salty and fresh. Like land plants they contain chlorophyll and need sunlight, and they are the base of several aquatic food webs.

How they live

• Most phytoplankton are buoyant and float in the upper part of the ocean, where sunlight penetrates the water.
• They use photosynthesis to turn sunlight into chemical energy. They consume carbon dioxide, and release oxygen.
• They also require inorganic nutrients such as nitrates, phosphates, and sulfur, which they convert into proteins, fats, and carbohydrates.
• All phytoplankton photosynthesize, but some get additional energy by consuming other organisms.

What they are

The name comes from the Greek words phyto (plant) and plankton (made to wander or drift). Some phytoplankton are bacteria, some are protists, and most are single-celled plants. Common kinds include cyanobacteria, silica-encased diatoms, dinoflagellates, green algae, and chalk-coated coccolithophores.

Diatoms and dinoflagellates

The two main classes of phytoplankton are dinoflagellates and diatoms.

• Dinoflagellates use a whip-like tail, or flagella, to move through the water, and their bodies are covered with complex shells.
• Diatoms also have shells, but made of a different substance, rigid and made of interlocking parts. Diatoms rely on ocean currents to travel through the water.

Claims

• id: C1 claim: Phytoplankton are microscopic marine algae. source: S1 evidence: "Phytoplankton are microscopic marine algae."
• id: C2 claim: Phytoplankton is the base of several aquatic food webs. source: S1 evidence: "Phytoplankton is the base of several aquatic food webs."
• id: C3 claim: Phytoplankton consume carbon dioxide and release oxygen. source: S2 evidence: "They consume carbon dioxide, and release oxygen."

Sources

• [S1] What are phytoplankton?. NOAA. https://oceanservice.noaa.gov/facts/phyto.html . License: US government work, public domain. Accessed 2026-11-04.
• [S2] What are Phytoplankton?. NOAA. https://earthobservatory.nasa.gov/features/Phytoplankton . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_td9p39yn,
  author = {{iinventedlight}},
  title = {{Phytoplankton: the drifting base of ocean food webs}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/phytoplankton/},
  note = {Permanent ID iil:note:td9p39yn. License: CC-BY-4.0.},
}

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