Exam 2 Review

Question 1

What is a diatom?

Answer 1

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.

Question 2

What do diatoms use to form colonial chains?

Answer 2

Use long spines called setae to hook together.

Question 3

Why are diatoms important and what is their role in ecosystems?

Answer 3

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)

Question 4

What is a nickname for diatoms and why are they called that?

Answer 4

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.

Question 5

What are blooms and why do they occur?

Answer 5

Periods of rapid reproduction due to favorable conditions such as light and nutrients.

Question 6

What is diatomaceous ooze?

Answer 6

Comprised of abundant frustules that settle onto the sea floor.

Question 7

What are the classifications for diatoms?

Answer 7

Phylum Bacillariophyta
(Some argue Phylum Chrysophyta)
Class Diatomatae
Two distinct orders:
Order Centrales (Cretaceous to Recent)
Order Pennales (Paleocene to Recent)

Question 8

Centrales features:

Answer 8

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

Question 9

Pennales features:

Answer 9

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

Question 10

What are some morphological features of diatoms?

Answer 10

Frustules, Girdles, Values, & Raphe.

Question 11

What are some features of a frustule?

Answer 11

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.

Question 12

What are some features of the valve?

Answer 12

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

Question 13

What are some areolation patterns?

Answer 13

1. A) radial, single areola
2. B) secondary rows in spirals
3. C) pinwheel-like areolation
4. D) pinwheel-like areolation
5. E) straight rows
6. F) rows concave towards margin

Question 14

What are raphe and where are they found?

Answer 14

Long groove that extends most of the length of the valve.
Only found in pennate diatoms, in which some secrete mucus used for motility.

Question 15

What kind of reproduction do diatoms conduct?

Answer 15

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

Question 16

How do diatoms receive nutrients?

Answer 16

Photosynthesis
i. Almost exclusively photosynthetic organisms
ii. HOWEVER some species practice mixotrophy or heterotrophy.
Heterotrophic species occur at certain depths.

Question 17

What is the distribution of diatoms?

Answer 17

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

Question 18

What areas can diatoms live within the world?

Answer 18

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.

Question 19

What are limiting factors for diatoms?

Answer 19

i. Light
ii. Temperature
iii. Salinity
iv. pH
v. Silicon
vi. Nitrate and phosphates
vii. Exudates
viii. Resting stage (Auxospores)

Question 20

Why is light a limiting factor?

Answer 20

Absorb blue light better than other phytoplankton.
Diatoms therefore able to photosynthesize deeper in the water column.

Question 21

Why is temperature a limiting factor?

Answer 21

Wide range of temperature tolerances.
Other environmental factors have stronger influence on distribution.

Question 22

Why is salinity a limiting factor?

Answer 22

Many species very tolerant to salinity changes.
Nearshore species especially tolerant.
Many genera have both freshwater and marine representatives.

Question 23

Why is pH a limiting factor?

Answer 23

Diatoms take up CO2 and therefore increase pH locally.
Silica more soluble under alkaline conditions.

Question 24

Why is silicon a limiting factor?

Answer 24

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.

Question 25

Why are nitrates and phosphates a limiting factor?

Answer 25

Require by diatoms.
Diatoms can utilize nitrates, nitrites, or ammonia.
Also capable of utilizing sulfur, manganese; boron and barium in some species.

Question 26

What is an exudate?

Answer 26

Compounds secreted by diatom.
Important in reducing competition, protection.

Question 27

Why are auxospores a limiting factor?

Answer 27

Many species of diatoms can produce cysts or resting stages (right) to survive adverse conditions.

Question 28

What is diatom taphonomy?

Answer 28

Most diatom dissolution occurs in upper 250 m of the water column (90-99% dissolve before reaching the floor).
Fossil assemblages are therefore rarely similar to original life assemblages
Certain species are more resistant.

Question 29

What is chert?

Answer 29

Diatoms dissolve during diagenesis.
Silica skeletal material is then reprecipitated.
This is one of the common ways in which the rock chert is formed.

Question 30

What occurred to diatoms during the Mesozoic era?

Answer 30

Jurassic Period
First diatom fossils date back 180 million years ago.
First diatoms were all centric.
Early centrics were heavily silicified.
Probably benthic and coastal.

Question 31

What occurred to diatoms during the Mesozoic era?

Answer 31

Cretaceous Period
First rich diatom assemblages are in Early Cretaceous.
Most diverse and best preserved are 110 Ma assemblages from Antarctica.
All centrics, none of which belong to any of the modern families.
Dominant modes of life: benthic, filamentous colonial forms, in shallow marine environments.

Question 32

What happened to diatoms during the Mesozoic era?

Answer 32

Gap in the diatom record.
Next well-preserved assemblages date to 90 Ma.
90 Ma assemblages known from a number of localities.
Include genera from modern families.
Biostratigraphic zonations developed.
Late Cretaceous has rich & widespread diatom accumulations.

Question 33

What happened to diatoms during the K-Pg boundary extinction?

Answer 33

Diatoms did not suffer much, sources say survival rates range from 37-84%.
Most likely due to resting stage.