What Phylum do coral belong to?
-Scleractinia
What are the names of coral’s two embryonic cell layers?
-epidermis and gastrodermis
What are the four tissue layers in an adult coral, and what are their embryonic origin?
- oral ectoderm, aboral ectoderm, oral endoderm, aboral endoderm
- evolved from endoderm and ectoderm, originally two circles
What cell types are present in each tissue layer of a coral?
- epidermis: cnidocytes with nematocysts, mucus secreting cells, interaction with bacteria
gastrodermis: algae-hosting cells
calicodermis: calcifying cells (make the skeleton), desmocytes (anchor tissue to skeleton)
What are the main physiological functions of each tissue layer?
- epidermis: fire nematocysts when provoked or to capture prey, interact with bacteria
gastrodermis: contain zooxanthellae
calicodermis: precipitate the skeleton and anchor the corals
What are cnidocytes and nematocysts? How are nematocysts fired?
- cnidocyte: Cell that produces and contains the nematocyst
- nematocysts: tiny osmotically-driven venomous harpoons
- Ca2+ is released into the cnidocytes, so water diffuses into this area of higher osmolarity, forcing the nematocyst out rapidly
How do coral obtain carbohydrates? And nitrogen?
- the coral holobiont fixes nitrogen (~20%)
- heterotrophy provides the other 80%
- photosynthesis by symbiotic algae provides more than 100% of needed carbohydrates
Mention three functions of the bacteria that live in the mucus at the coral surface
- Nitrogen fixation
- Phosphate and sulfur cycling
- Niche occupation
How are symbiotic algae acquired? In which coral cell type are symbiotic algae hosted? What is the symbiosome?
- cnidarians pass large volumes of water through their gastrovascular system for respiration and waste removal, the water contains free-living Symbiodiniums pp. OR
- coral gastrodermal cells pick up specific symbiodiniumstrains from the coelenteron (gastrovascular cavity)
- contained in gastrodermis
- symbiosome is space where symbiotic algae are kept
What are the two domains that comprise the vacuolar proton pump? (VHA). What is the function of each domain?
- V1 domain = rotating head that hydrolyzes ATP => provides the energy for H+ movement
- V0 domain = makes a channel across the membrane that allows H+ movement
What is an advantage of excreting acid using VHA instead of by secondarily active transport by NHE & NKA?
-VHA can secrete H+against a steeper gradient compared to secondary active transport powered by NKA
Where is the VHA located in coral cells? What is the physiological role of VHA in that compartment?
- abundantly expressed in the coral symbiosome membrane of coral gastrodermal cells
- VHA activity acidifies the symbiosome space
“Bleaching” is one a coral colony loses the majority of its algal symbionts. How do you predict it will affect its energy metabolic pathways?
- it loses its main energy source, will rely more heavily on heterotrophic mechanisms
- would react similarly to anoxic conditions, try to preserve ATP
What coral tissue layer makes the skeleton? What are the two cell types in that epithelium?
- calicoblastic epithelium
- cell types are calcifying cells (make the calcium carbonate skeleton) and desmocytes (anchor coral tissues to skeleton)
What is the “aragonite saturation state” and how does it relate to calcification?
- a measure of how likely is aragonite to precipitate (the higher, the better for calcification)
- numbers greater than 1 indicate precipitation and less than 1 are dissolution
What are the two potential pathways for [Ca2+] transport to the site of calcification?
- Paracellular pathway (in between cells)
- Transcellular vesicles
What would happen if Ca2+ was transported through the cytoplasm of calcifying cells on their way to the skeleton?
- high intracellular [Ca2+] would precipitate with phosphates making crystals that would kill the cell
- high intracellular [Ca2+] may trigger apoptosis
What are the two pathways for DIC transport to the site of calcification?
- HCO3- from mitochondrial CO2 (from aerobic respiration, catalyzed by carbonic anhydrase)
- from the coelenteron
What are two ways in which coral decrease the aragonite solubility constant (Ksp) at the site of calcification? How does this promote calcification?
- isolate calcifying site from seawater
- produce proteins that favor CaCO3 precipitation (“nucleation proteins”)
Describe how acidic pH favors photosynthesis, and how alkaline pH favor calcification.
- Extreme and opposite pHs in symbiosome and SCM respectively drive photosynthesis and calcification in coral
- ph 4 promotes CO2 formation and photosynthesis at surface of coral
- ph 9 promotes CO32- formation and calcification at skeleton
- differing pH changes the favorable form of DIC
