Diatoms are a common type of unicellular or colonial phytoplankton that are primary producers in food chains. They are made of silica and have a pillbox or petri-dish shape. There are over 200 genera of living diatoms, with approximately 100,000 species found in freshwater and marine environments. Diatoms come in various sizes, from individual cells to colonies several feet long, and have two basic shapes: radial centric diatoms and bilaterally symmetrical pennate diatoms.

1. BIO 14 YA
June 29, 2013

2. • Eukaryotic algae
• Common type of
phytoplankton
• Unicellular or colonies
• Primary producers in the
food chain
• Over 200 genera of living
diatoms, and approximately
100,000 species
• Found in freshwater and
marine environments

3. • Made up of silica
• Called “Frustule”
• Pillbox or petri-dish in
shape
• Epitheca vs Epivalve
• Hypotheca vs Hypovalve
• Mid junction = girdle

4. • Do not tend to have a
strong, highly visible
color
• In groups, yellowish –
golden in color
• In larger groups, deep
brown or black

5. • Very diverse in size
• Can form colonies
and filaments to two
feet!
• Two types of diatoms
based on shape:
•Centric
•Pennate

6. • Radial symmetry
• Primitive
• Raphe Absent
• Almost immoblie
• Large vacuole with
many discoid
cloroplasts

7. • Bilateral symmetry
• Boat-shaped
• Raphe/pseudoraph
e is present
• Few elongated
chloroplasts
• advanced

8. • Strands of mucilage
are secreted
through the raphe
• Strands attach cells
to substrate
• Cells glide over the
substrate

10. • Cell division
• Daughter cells
receiving the
hypovalve are
smaller
• Daughter cells
receiving the
epivalve are the
same with the
parent

12. • Planktonic
• All centric and some pennate
• Benthic
• Pennates, these secrete mucilage to
form biofilm
• Meroplanktonic
• Temporary, during periods of
turbulence they are carried out in the
open water

13. • Diatoms produce an estimated 20% to
25% photosynthesis on the planet
• A major food resource for marine and
freshwater microorganisms and animal
larvae
• A major source of atmospheric
oxygen

14. • Richest source of
diatom fossils are
deposits of their
skeletons known as
diatomite or
diatomaceous earth
• Mined for
cleansers, paints, filte
ring agents, abrasives
and toothpastes

15. http://www.nanowerk.com/news/newsid=1591.
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