Student Resources

Jawed Fishes -Workbook Questions

Why is countercurrent flow of blood and water better than concurrent flow of the two?  (p. 110)

For exchange to occur between the two fluids, there has to be a concentration difference between them as they flow past each other. If they are flowing in the same direction, concurrent flow, exchange will occur until both fluids reach the same concentration. For example, if one fluid is at 10 percent of its capacity and the other is at 90 percent, then there will be a point where both reach 50 percent; after that there will no longer be any exchange. This doesn’t happen in concurrent flow where the two fluids involved in exchange are flowing in opposite directions. In this case, one fluid is always moving upstream compared to the other and will find itself adjacent to a higher concentration of the substance being exchanged. Exchange occurs across the whole length of the system, and there’s no point where equilibrium concentrations can occur between the two fluids. 

What are the different types of caudal fins, and which types are found in the two classes of jawed fish?  (p. 111)

There are three types of fish tails: heterocercal, diphycercal, and homocercal fins. A heterocercal fin has a dorsal lobe that is much larger than the ventral lobe, and the vertebral column extends up and into the dorsal lobe of the fin. The dorsal and ventral lobes of the diphycercal fin are similar in size, and the vertebral column is found between the two lobes. A homocercal fin has equally sized and shaped dorsal and ventral lobes but with a reduced, narrowed vertebral column that supports the fin’s dorsal most edge. Sharks, and similar chondrichthyes, have heterocercal tails; the diphycercal tails are found in lungfish and their relatives; and the homocercal tail is characteristic of bony fish. 

What is a shark’s spiral valve, and what does it do?  (p. 112)

A shark’s spiral valve is part of its digestive system, a modification of the ileum. The wall of the intestine is folded creating a helical spiral through the center that slows the passage of food through this part of the intestine. The spiral also increases the surface area for absorption, and the combination of a larger surface area and slower movement of food increases the digestive performance of the intestine. A good analogy for the differences between a straight tube and spiral valve is how quickly you could get from the second to the first floor of a building sliding down a pole or using a spiral staircase. 

What is the main metabolic waste in sharks, and how is it used for osmoregulation?  (p. 112)

The main metabolic waste in sharks is urea. The ancestor of the cartilaginous fishes was a freshwater fish that was hypoosmotic to the new marine environment. To overcome the problems of potential water loss by diffusion across gills, and other surfaces, cartilaginous fishes retain high levels of urea in their body fluids. The result is that they are osmotically isotonic, or slightly hyperosmotic, to the surrounding ocean water. 

How does a shark achieve a neutral buoyancy?  (p. 113)

Oils with a lower density than water will float, and shark oil, squalene, has a specific gravity of 0.86--water is 1.00. Sharks synthesize and store large amounts of squalene in their liver; it’s why their liver is so large and the overall average of specific gravity from body tissue (around 1.1) and squalene brings the animal close to that of water and creates neutral buoyancy. 

Protozoa || Porifera || Cnidaria || Platyhelminthes || Nematoda || Annelida || Mollusca || Arthropoda
Echinodermata || Chordate Origins || Jawed Fishes || Amphibia || Mammalia