Exam 2 Review Flashcards
What is a diatom?
a. Unicellular protists
b. Constructs distinct silica wall called frustule
c. Abundant in freshwater and marine settings
d. Most ~10-200 µm in size
e. Individuals can form colony-like chains that can be 7 cm or more in length.
What do diatoms use to form colonial chains?
Use long spines called setae to hook together.
Why are diatoms important and what is their role in ecosystems?
Very important PRIMARY PRODUCERS in temperate and polar regions.
i. Major component of plankton and major food source to many others.
Responsible for 20-25% of global carbon fixation (CO2 + H2O = sugars)
What is a nickname for diatoms and why are they called that?
The grass of the sea. Called so because they are the lowest part of the food chain in which they’re primary producers and a source of food for plankton and other organisms.
What are blooms and why do they occur?
Periods of rapid reproduction due to favorable conditions such as light and nutrients.
What is diatomaceous ooze?
Comprised of abundant frustules that settle onto the sea floor.
What are the classifications for diatoms?
Phylum Bacillariophyta
(Some argue Phylum Chrysophyta)
Class Diatomatae
Two distinct orders:
Order Centrales (Cretaceous to Recent)
Order Pennales (Paleocene to Recent)
Centrales features:
Centric: structural center is a POINT (dot)
i. Surface features arranged around central point
ii. Can be: circular, oblong, hemi-circular, triangular, quadrangular.
iii. More common in MARINE environments
Pennales features:
Pennales: structural center is a line
i. Bilaterally symmetrical features perpendicular to long axis.
ii. (Elongated) diatoms
iii. Better adapted for movement
iv. Dominate freshwater environments
What are some morphological features of diatoms?
Frustules, Girdles, Values, & Raphe.
What are some features of a frustule?
Primary skeletal structure that’s made of opaline or biogenic silica (SiO2)
Consists of overlapping values that can be divided into:
1. Hypotheca- the lower box
2. Epitheca- the upper lid
3. Girdle- the overlapping sides
Is transparent for photosynthetic purposes.
What are some features of the valve?
i. Areola (singular)
ii. Pores in frustule that an be circular, elliptical, hexagonal, ect.
iii. Arranged in pore fields.
1. Areas without pores are hyaline fields
iv. Different Areolation Patterns
What are some areolation patterns?
- A) radial, single areola
- B) secondary rows in spirals
- C) pinwheel-like areolation
- D) pinwheel-like areolation
- E) straight rows
- F) rows concave towards margin
What are raphe and where are they found?
Long groove that extends most of the length of the valve.
Only found in pennate diatoms, in which some secrete mucus used for motility.
What kind of reproduction do diatoms conduct?
Asexual and Sexual Reproduction.
i. Alternation of generations in both sexual and asexual stages
1. Tied critically to diatom size
ii. Asexual Reproduction produces smaller diatoms as time goes on.
iii. Sexual Reproduction produces gradually larger diatoms.
b. Resting Stages
How do diatoms receive nutrients?
Photosynthesis
i. Almost exclusively photosynthetic organisms
ii. HOWEVER some species practice mixotrophy or heterotrophy.
Heterotrophic species occur at certain depths.
What is the distribution of diatoms?
i. Freshwater: lacustrine, swamp, marsh, riverine
ii. Marine: shoreline environments to the deep sea
iii. Other:
1. Damp terrestrial
2. Hot springs
3. Hypersaline lakes
4. Melt-water pools on icebergs
What areas can diatoms live within the world?
iv. Southern Ocean: Between 45 and 65°S
v. Northern belt
1. Pacific: Sea of Okhotsk, Sea of Japan, Bering Sea
2. Atlantic: (Norwegian Sea)
vi. Equatorial belt
1. Pacific and Indian Oceans
2. Less so in the Atlantic.
What are limiting factors for diatoms?
i. Light
ii. Temperature
iii. Salinity
iv. pH
v. Silicon
vi. Nitrate and phosphates
vii. Exudates
viii. Resting stage (Auxospores)
Why is light a limiting factor?
Absorb blue light better than other phytoplankton.
Diatoms therefore able to photosynthesize deeper in the water column.
Why is temperature a limiting factor?
Wide range of temperature tolerances.
Other environmental factors have stronger influence on distribution.
Why is salinity a limiting factor?
Many species very tolerant to salinity changes.
Nearshore species especially tolerant.
Many genera have both freshwater and marine representatives.
Why is pH a limiting factor?
Diatoms take up CO2 and therefore increase pH locally.
Silica more soluble under alkaline conditions.
Why is silicon a limiting factor?
An absolute requirement for diatoms.
Silica never absent from seawater, but heavy diatom productivity may lower levels .
In cultures, diatom activity will result in dissolution of glass containers.
