Phytoplankton Eukaryotic autotrophs A large part of the freshwater and marine autotrophic community Drift or swim near water surface Most common primary producer in aquatic environments Phytoplankton are at the bottom of most aquatic food chains Can be the cause of dead zones, comparable to Algal blooms

Diatoms

Diatoms Formation: Typically unicellular Can form colonies, which are held together by spines Usually reproduce asexually through mitosis, sexual reproduction is rare Can form colonies which are held together by spines Thousands of different species of diatoms, Estimated 100,000 Move by gliding caused by interactions between the contractile protein and filaments

Diatoms Structure: Mesh-like Enclosed by a unique hydrated silica-glasslike wall (frustule) Wall has two parts, comparable to a shoebox and lid Bouyancy is maintained by cellular regulation of ions, which counteract the weight of the walls Store food as a glucose polymer called laminarin or as oils

Importance to Earth’s Life Cycle and Photosynthesis Diatoms are photosynthetic and found anywhere with water A bucket of water from the surface of the sea can contain millions of diatoms That many microscopic photosynthesizing diatoms means that they produce almost 25% of the oxygen we breathe Second most abundant photosynthesizing group, after angiosperms Diatoms chloroplasts contain special pigments that cause them to be golden brown in color