lecture 9 (diatoms) Flashcards
what are stramenopiles, what is a unifying characteristic
brown algae, golden brown diatoms etc. also known as heterokonts.
unifying feature = two flagella that are different in length and ornamentation in vegetative or reproductive cells
describe stramenopile flagella and their function in terms of movement
heterokont flagella
one long, forwards directed flagellum with hairs (pulls forwards)
one shorter, smooth flagellum (“rudder”)
why are diatoms so important in the ecology of the ocean?
hugely abundant, drive the biological carbon pump (responsible for over 20% of C fixation), responsible for ~40% of the oceans PP. huge part of sediment accumulation (diatomaceous earth)
in which environments do planktonic diatoms flourish?
cold, nutrient rich waters (marine upwelling), and recently circulated lake waters (but can also be found under/in polar ice)
what are the two main diatom forms?
pennate (oval shape, bilateral symmetry) and centric (like a Petrie dish, radially symmetrical)
what are the advantages of a cell wall to diatoms?
herbivore defense (sometimes spikey), protection, inert to enzymatic attack
what is the frustule made of?
2 valves of silica (SiO2) which can be highly ornamented
what dinoflagellate causes damage to fish gills
Chaetoceras
araphid vs raphid diatoms
pennate diatoms without (araphid) or with (raphid) a raphe
raphid have a raphe system (longitudinal slits) for gliding motility
epitheca
the top valve of a diatom with the epivalve and epicingulum
hypotheca
the bottom half of a diatom with the hypovalve and hypocingulum
diatom cingulum
the girdle (with girdle bands)
aerolae definition and function
pores that penetrate the diatom frustrule
function: movement of gases, nutrients etc.
rimoportulae or labiate processes definition and function
tubular, passes through the valve of diatoms and the inside end is lipped
function: polysaccharide excretion (attachment/movement)
fultoportulae definition and function
central strutted processes without an external extension
function = secretion of chitin fibrils for flotation
where are girdle bands?
they run around the diatom frustule, visible from the girdle view (side)
can diatoms produce toxic blooms?
yes
describe asexual reproduction in diatoms
the parent cells and girdle bands lie outside the newly forming daughter valves, with each of the daughter valves enclosed in silicalemma.
new valve is always the hypotheca (smaller valve)
this decreases the size over several generations
when is sexual reproduction of diatoms triggered?
when the diatoms reach about 1/3 the size of the maximal size
describe sexual reproduction of diatoms, and its role in size regeneration
dependent on many environmental cues, when diatom is too small, then produces an auxospore which restores the typical cell with maximum size
describe the life cycle of centric diatoms
gametic life cycle, oogamous (1-2 eggs per parental cell, 4-128 flagellated sperm per parental cell).
gametes fuse, creating a zygote which becomes a large auxospore
describe the life cycle of a pennate diatom
gametic life cycle isogamous (2 ameboid gametes, similar in size, no flagella)
begins with pairing of parental cells in a common mucilage (4 parental halves in a group).
frustules open, protoplasts and nuclei fuse to create an auxospore
ways that diatoms can slow sinking
small size and appendages, formation of chains, oil droplets, ionic regulation
diatom pigments
chl a, chl c, b-carotene, xanthophylls (especially fucoxanthin)
