BIO 14 YA

June 29, 2013

• 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

• Made up of silica

• Called “Frustule”

• Pillbox or petri-dish in

shape

• Epitheca vs Epivalve

• Hypotheca vs Hypovalve

• Mid junction = girdle

• Do not tend to have a

strong, highly visible

color

• In groups, yellowish –

golden in color

• In larger groups, deep

brown or black

• Very diverse in size

• Can form colonies

and filaments to two

feet!

• Two types of diatoms

based on shape:

•Centric

•Pennate

• Radial symmetry

• Primitive

• Raphe Absent

• Almost immoblie

• Large vacuole with

many discoid

cloroplasts

• Bilateral symmetry

• Boat-shaped

• Raphe/pseudoraph

e is present

• Few elongated

chloroplasts

• advanced

• Strands of mucilage

are secreted

through the raphe

• Strands attach cells

to substrate

• Cells glide over the

substrate

• Cell division

• Daughter cells

receiving the

hypovalve are

smaller

• Daughter cells

receiving the

epivalve are the

same with the

parent

• 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

• 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

• 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

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