Lecture 11 (Calcification)

Question 1

What is coral calcification?

Answer 1

The complex process by which corals take calcium from the seawater and form aragonite or calcite crystals to be used in skeletogenesis (reef growth)

Question 2

Coral calcification occurs in individual ______

Answer 2

polyps (CaCO3 layers right below the polyp)

Question 3

Coral calcification occurs best in _______ waters

Answer 3

warmer (due to carbonate chemistry)

Question 4

What are the 3 interchangeable terms for calcium carbonate?

Answer 4

1) Calcium carbonate
2) CaCO3
3) Limestone

Question 5

What are the 2 forms of crystalline that CaCO3-secreting organisms can produce?

Answer 5

1) Aragonite
2) Calcite

Question 6

Aragonite vs. calcite crystalline

Answer 6

1) Aragonite is stronger
2) Have differing stabilities depending on T and P
3) Aragonite more readily ppt in warmer waters (where more CaCO3 is), less stable in cooler or fresh water
4) Calcite more present in ancient limestones (aragonite dissolves over time)

Question 7

Chemical equation for calcification

Answer 7

Ca2+ + CO32- —–> CaCO3

Question 8

Chemical equation of CO2 with water

Answer 8

Co2 + H2O —> H2CO3 —> H+ + HCO3- —> 2H+ + CO32-

Question 9

What are the 4 states present in surface seawater (making it a buffer system)?

Answer 9

1) Carbon dioxide
2) Carbonic acid
3) Bicarbonate
4) Carbonate

Question 10

Amounts of CO2 that can initially dissolve depends on ________, _________, and ____________

Answer 10

temperature, pressure, concentrations of other dissolved materials

Question 11

Reaction of carbon dioxide and water with calcium carbonate

Answer 11

CO2 + H2O + CaCO3 -> Ca2+ + 2HCO3-

Question 12

T/F: The more CO2 that is dissolved into the water, the more readily water can dissolve CaCO3

Answer 12

T (this makes warmer water less likely to ppt CaCO3 and colder more likely to ppt)

Question 13

T/F: The deeper in the ocean you go, the more CO2 stays in solution

Answer 13

T (the surface of the ocean is the best place for CaCO3 ppt. Deep, cold water is the worst)

Question 14

Where does Ca2+ come from?

Answer 14

The weathering of basalt

Question 15

Dissolved silica ppts and from opal

Answer 15

1) opal –> quartz
2) CaCO3 –> limestone –> marble

Question 16

Where does calcification take place?

Answer 16

Below the epithelial layers of the coral polyp

Question 17

Calcification requires _______ energy transport

Answer 17

active (energy requiring, not passive)

Question 18

What is the process for calcification/skeletogenesis?

Answer 18

1) Ca2+ enters through the gut
2) Ca2+ actively transported to ECF

Question 19

4 possible ways for Ca2+ to enter skeleton

Answer 19

1) Bicarbonate enters gut, combines with proton to from CO2, which is able to diffuse across the epithelium, where it is converted into carbonate
2) Bicarbonate pumped across epithelium to ECF, where it is converted to carbonate
3) Coral respiration
4) Ca2+/ATPase

Question 20

Process of Ca2+ becoming skeleton

Answer 20

1) Ca2+ ions taken up by coral from seawater
2) CO2 from respiration combines with water to form carbonate
3) Ca2+ and carbonate form calcium bicarbonate (which is unstable and breaks down into CaCO3)
4) CaCO3 deposited as skeleton

Question 21

What are L-channels?

Answer 21

1) L-type voltage-dependent Ca2+ channels are proteins found in the membranes of certain cells (including corals)
2) They open in response to changes in voltage across the cell membrane, allowing Ca2+ to flow into the cell from sea water

Question 22

How do coral polyp and zooxanthellae help with calcification?

Answer 22

1) Raising the supersaturation of Ca and carbonate, increase ppt
2) Maintain a fresh crystal face of aragonite to act as a seed
3) Inhibit Mg, PO4- and other organics that inhibit crystal formation
4) Help direct with their own proteins and polysaccs. secreted in ECF

Question 23

Calcification produces CO2, but _____________ consume it

Answer 23

zooxanthellae

Question 24

A partial pressure of CO2 increases, calcification __________

Answer 24

decreases (negatively impacted by rising sea levels