1. 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

2. Diatoms

3. 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

4. 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

5. 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