Topic 9: Diatoms Flashcards
- What are stramenopiles?
Defined in terms of flagellar ultrastructure or molecular data
Known as heterokonts: 2 different flagella in both vegetative and reproductive cells
- Why are diatoms so important in the ecology of the oceans?
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
- In which environments do planktonic diatoms fluorish?
Dominant in cold well circulated marine waters (nutrient rich)
Rich communities under polar ice
Recently circulated lakes
- Describe the two main diatom forms.
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)
- Describe the different parts of the cell wall in diatoms.
Protoplast enclosed in frustule (theca)
2 valves of silica (SiO2) organic coating
Highly ornamented
- What advantages does the cell wall confer to a diatom cell?
Inert to enzymatic attack
Protection and grazing deterrent
Si is often plentiful and energetically inexpensive
- What is the frustule made of?
2 Overlapping components
Epitheca – epivalve and epiclingulum
Hypotheca – hypovalve and hypoclingulum
Clingulum – girdle
Primarily composed of silica
- Can diatoms produce toxic blooms?
Yes they can produce toxic blooms
- Describe asexual reproduction in diatoms.
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
- Explain with a labeled diagram the typical reduction in cell size that diatoms experience over several generations of mitotic cell division.
- 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
- What is the effect of sexual reproduction on diatom cell size?
It is essential for size regeneration
It is dependent on environmental variables
- How do benthic pennate diatoms move?
Use of raphe
Rapid movement: Jerky raphe movement (0.2-0.25μm/s)
Secrete mucous then attach to substrate and pull along
- Describe the different ways in which planktonic diatoms can retard sinking.
Small size and appendages
Formation of chains
Oil droplets
Ionic regulation
- Can diatom spores develop under low Si availability?
NO
THEY CANNOT DEVELOP
Only resting cells can
- Describe the following terms: raphe, areolae, rimoportulae, silica deposition vesicle, resting cell.
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
- What is the distinctive accessory pigment in diatoms?
NOT SURE WHAT IS DISTINCT
Has Chl a and c
beta carotene
fucoxanthin
- Under what environmental conditions do diatoms typically switch to heterotrophic nutrition?
Under low irradiance and high dissolved organics
- Why are diatoms so successful in the early spring in temperate oceans and in upwelling zones of all oceans?
Thrive in nutrient-rich and turbulent waters
Very fast growing in these environments
NOT TOTALLY SURE ABOUT THIS ONE
- Where are biogenic siliceous sediments most common in the oceans
Subarctic Pacific, Southern Ocean and upwelling areas
- What does the term “silicate ocean” refer to?
Refers to the dominance of diatoms (Silicate forming) in those oceans rather than Coccolithophores
- What “kind” of ocean (silicate or carbonate) normally has greater carbon export to deep waters? Why?
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
