Topic 9: Diatoms

Question 1

• What are stramenopiles?

Answer 1

Defined in terms of flagellar ultrastructure or molecular data
Known as heterokonts: 2 different flagella in both vegetative and reproductive cells

Question 2

• Why are diatoms so important in the ecology of the oceans?

Answer 2

Toxin producing
Most abundant eukaryotic aquatic organism and one of most important aquatic photosynthesizer
20% of C fixation on earth and 40% of marine primary productivity
Massive sedimentary accumulation and oil

Question 3

• In which environments do planktonic diatoms fluorish?

Answer 3

Dominant in cold well circulated marine waters (nutrient rich)
Rich communities under polar ice
Recently circulated lakes

Question 4

• Describe the two main diatom forms.

Answer 4

Centric: discoid or cylindrical cells, radial symmetry, many discoid plastids

Pennate: Bilateral symmetry, two large-plate like plastids, raphid pennates (raphe system for gliding), araphid pennates (no raphe system)

Question 5

• Describe the different parts of the cell wall in diatoms.

Answer 5

Protoplast enclosed in frustule (theca)
2 valves of silica (SiO2) organic coating
Highly ornamented

Question 6

• What advantages does the cell wall confer to a diatom cell?

Answer 6

Inert to enzymatic attack
Protection and grazing deterrent
Si is often plentiful and energetically inexpensive

Question 7

• What is the frustule made of?

Answer 7

2 Overlapping components
Epitheca – epivalve and epiclingulum
Hypotheca – hypovalve and hypoclingulum
Clingulum – girdle

Primarily composed of silica

Question 8

• Can diatoms produce toxic blooms?

Answer 8

Yes they can produce toxic blooms

Question 9

• Describe asexual reproduction in diatoms.

Answer 9

Via cell division, forms valve (dependent on Si)
Silica deposition vesicle – new valves – hypothecas
Over many generations the average size decreases
At ~1/3 max size sexual reproduction is triggered

Question 10

• Explain with a labeled diagram the typical reduction in cell size that diatoms experience over several generations of mitotic cell division.

Question 11

• Describe with a labeled diagram the life cycle of a (i) centric and (ii) pennate diatom. In each case, indicate the type of life cycle

Question 12

• What is the effect of sexual reproduction on diatom cell size?

Answer 12

It is essential for size regeneration
It is dependent on environmental variables

Question 13

• How do benthic pennate diatoms move?

Answer 13

Use of raphe
Rapid movement: Jerky raphe movement (0.2-0.25μm/s)
Secrete mucous then attach to substrate and pull along

Question 14

• Describe the different ways in which planktonic diatoms can retard sinking.

Answer 14

Small size and appendages
Formation of chains
Oil droplets
Ionic regulation

Question 15

• Can diatom spores develop under low Si availability?

Answer 15

NO
THEY CANNOT DEVELOP
Only resting cells can

Question 16

• Describe the following terms: raphe, areolae, rimoportulae, silica deposition vesicle, resting cell.

Answer 16

Raphe: In many pennates, longitudinal slits, associated with movement

Areolae: Pores that penetrate frustule. Function for movement of gases, nutrients

Rimoportulae: Tubular, passes through valves, inside ends in slit. Function: polysaccharide excretion (attachment, movement)

SIlica Deposition Vesicle: This creates new valves which form hypothecas. Essential for cell division

Resting Cell: Similar to vegetative cells, can form under low Si, freshwater diatoms and pennates

Question 17

• What is the distinctive accessory pigment in diatoms?

Answer 17

NOT SURE WHAT IS DISTINCT
Has Chl a and c
beta carotene
fucoxanthin

Question 18

• Under what environmental conditions do diatoms typically switch to heterotrophic nutrition?

Answer 18

Under low irradiance and high dissolved organics

Question 19

• Why are diatoms so successful in the early spring in temperate oceans and in upwelling zones of all oceans?

Answer 19

Thrive in nutrient-rich and turbulent waters
Very fast growing in these environments
NOT TOTALLY SURE ABOUT THIS ONE

Question 20

• Where are biogenic siliceous sediments most common in the oceans

Answer 20

Subarctic Pacific, Southern Ocean and upwelling areas

Question 21

• What does the term “silicate ocean” refer to?

Answer 21

Refers to the dominance of diatoms (Silicate forming) in those oceans rather than Coccolithophores

Question 22

• What “kind” of ocean (silicate or carbonate) normally has greater carbon export to deep waters? Why?

Answer 22

Silicate oceans have greater carbon export!
Silica sinks faster and does not dissolve as much
Fast growth rate of diatoms pulls in carbon then sinks