lecture 9 (diatoms)

Question 1

what are stramenopiles, what is a unifying characteristic

Answer 1

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

Question 2

describe stramenopile flagella and their function in terms of movement

Answer 2

heterokont flagella
one long, forwards directed flagellum with hairs (pulls forwards)
one shorter, smooth flagellum (“rudder”)

Question 3

why are diatoms so important in the ecology of the ocean?

Answer 3

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)

Question 4

in which environments do planktonic diatoms flourish?

Answer 4

cold, nutrient rich waters (marine upwelling), and recently circulated lake waters (but can also be found under/in polar ice)

Question 5

what are the two main diatom forms?

Answer 5

pennate (oval shape, bilateral symmetry) and centric (like a Petrie dish, radially symmetrical)

Question 6

what are the advantages of a cell wall to diatoms?

Answer 6

herbivore defense (sometimes spikey), protection, inert to enzymatic attack

Question 7

what is the frustule made of?

Answer 7

2 valves of silica (SiO2) which can be highly ornamented

Question 8

what dinoflagellate causes damage to fish gills

Answer 8

Chaetoceras

Question 9

araphid vs raphid diatoms

Answer 9

pennate diatoms without (araphid) or with (raphid) a raphe
raphid have a raphe system (longitudinal slits) for gliding motility

Question 10

epitheca

Answer 10

the top valve of a diatom with the epivalve and epicingulum

Question 11

hypotheca

Answer 11

the bottom half of a diatom with the hypovalve and hypocingulum

Question 12

diatom cingulum

Answer 12

the girdle (with girdle bands)

Question 13

aerolae definition and function

Answer 13

pores that penetrate the diatom frustrule
function: movement of gases, nutrients etc.

Question 14

rimoportulae or labiate processes definition and function

Answer 14

tubular, passes through the valve of diatoms and the inside end is lipped
function: polysaccharide excretion (attachment/movement)

Question 15

fultoportulae definition and function

Answer 15

central strutted processes without an external extension
function = secretion of chitin fibrils for flotation

Question 16

where are girdle bands?

Answer 16

they run around the diatom frustule, visible from the girdle view (side)

Question 17

can diatoms produce toxic blooms?

Answer 17

yes

Question 18

describe asexual reproduction in diatoms

Answer 18

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

Question 19

when is sexual reproduction of diatoms triggered?

Answer 19

when the diatoms reach about 1/3 the size of the maximal size

Question 20

describe sexual reproduction of diatoms, and its role in size regeneration

Answer 20

dependent on many environmental cues, when diatom is too small, then produces an auxospore which restores the typical cell with maximum size

Question 21

describe the life cycle of centric diatoms

Answer 21

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

Question 22

describe the life cycle of a pennate diatom

Answer 22

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

Question 23

ways that diatoms can slow sinking

Answer 23

small size and appendages, formation of chains, oil droplets, ionic regulation

Question 24

diatom pigments

Answer 24

chl a, chl c, b-carotene, xanthophylls (especially fucoxanthin)

Question 25

storage products of diatoms

Answer 25

chysolaminaran, lipids

Question 26

can diatom spores develop under low Si availability?

Answer 26

spores cannot, but resting cells can

Question 27

describe the differences between diatom resting cells and spores

Answer 27

resting cells: dormant state of vegetative cells, can develop under low Si, occurs in freshwater diatoms
spores: have thick frustule with less ornamentation, cannot develop under low Si, coastal marine centric diatoms

Question 28

describe the silica deposition vesicles

Answer 28

secretes the new valves which become hypothecas

Question 29

describe motility of diatoms

Answer 29

flagellar apparatus is highly reduced (present in some gametes)
benthic raphid pennates move using the raphe which extrudes strands of mucilage

Question 30

what is the distinctive accessory pigment in diatoms?

Answer 30

fucoxanthin

Question 31

what environmental conditions will cause diatoms to switch to heterotrophy?

Answer 31

low irradiance and high dissolved organics (eg. in the dark)

Question 32

why are diatoms so successful in early spring in temperate zones, and upwelling zones in oceans?

Answer 32

they need lots of nutrients, and upwelling brings silica that they need to grow up to the surface

Question 33

why are biogenic siliceous sediments most common in the oceans?

Answer 33

because freshwater diatoms don’t use as much silica

Question 34

what does the term “silicate ocean” refer to?

Answer 34

subarctic pacific, southern ocean, and upwelling areas where there is more sedimentation of SiO2 than CO3Ca

Question 35

what “kind” of ocean (silicate or carbonate) typically has greater carbon export to deep waters and why?

Answer 35

Silicate oceans have greater drawdown of carbon
this is because of the balance between photosynthesis and calcification (coccolithophores make CO2 in calfication process)

Question 36

what “kind” of ocean (silicate or carbonate) typically has greater carbon export to deep waters and why?

Answer 36

Silicate oceans have greater drawdown of carbon
this is because of the balance between photosynthesis and calcification (coccolithophores make CO2 in calfication process)