A diver notices that the sharks near a reef keep swimming all the time, while the rohu in a nearby…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A diver notices that the sharks near a reef keep swimming all the time, while the rohu in a nearby fish farm can hang still in the water. Explain the difference.
Need a reminder? The key ideaShow
Cyclostomata: no jaws, 6 to 15 pairs of gill slits, no scales, no paired fins. Chondrichthyes: cartilage, ventral mouth, separate gill slits with no operculum, placoid scales, no air bladder. Osteichthyes: bone, terminal mouth, four pairs of gills under an operculum, air bladder. Amphibia: moist skin without scales, cloaca, a three-chambered heart, gills, lungs and skin for breathing.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The rohu. It is a bony fish with an air bladder. By changing the gas in it, the rohu stays afloat at any depth without swimming.
Step 2. The shark. It is a cartilaginous fish, and it has no air bladder.
Step 3. The result. Without an air bladder, a shark would sink if it stopped. So it must keep swimming.
Answer: the rohu floats with its air bladder; the shark has no air bladder, so it keeps swimming to avoid sinking.
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