Question

23.) If a hagfish is placed in saltwater, what will happen to the fish? Explain your answer in terms of osmosis.

24.) In mating season, how do you distinguish a male frog from a female frog? What is the biological role of this feature/characteristic? What feature is it analogous to in the fish?

25.) Why are placoderms considered a "stand alone" group of gnathostomes?

Answer 1

Ques:If a hagfish is placed in saltwater, what will happen to the fish? Explain your answer in terms of osmosis.

Ans:  Hagfish are long, eel-like fish that live in salt water. The concentration of NaCl in body fluids of hagfish is approximately equal to that of seawater.Hagfish are osmoconformers, ie;they maintain an internal environment which is isotonic to their external environment.This means that the osmotic pressure of the organism's cells is equal to the osmotic pressure of their surrounding environment. By minimizing the osmotic gradient, this subsequently minimizes the net influx and efflux of water into and out of cells. By diffusion of water or solutes, osmotic balance ensures that optimal concentrations of electrolytes and non-electrolytes are maintained in cells, body tissues, and in interstitial fluid. Solutes or water move across a semi-permeable membrane, causing solutions on either side of it to equalize in concentration

Hence, Hagfish will survive and no prominent changes will occur if placed in saltwater.

Ques:  In mating season, how do you distinguish a male frog from a female frog? What is the biological role of this feature/characteristic? What feature is it analogous to in the fish?

Ans: The best time to distinguish male frogs from female frogs is during mating season. That's because the bulk of the unmistakable differences dictating gender are most apparent during reproductive activity.

Following are the aspects by which we can distinguish a male frog from a female frog during mating season specifically, and their biological feature:

(a) Size: For many frog species, the females are significantly larger than the males. This is to accommodate the amphibian mating process called amplexus. The male climbs on top of the female and she supports his weight as she discharges eggs and he spreads sperm on top of them. He is smaller so that his weight does not crush her. Her body is larger also to provide ample storage and transport room for the eggs.

(b)Male Only Behaviors: While eating habits, defensive maneuvers, use of camouflage and shedding of skin is the same for male and female frogs, there are a couple of behaviors that only male frogs engage in. The first is singing for a mate during the breeding season. The second is the "hugging" or "humping" aspect of amplexus. Male frogs don't restrict performing this behavior to only on female frogs. They will attach themselves to logs, rocks, trees, shoes and backpacks and hump until the mood passes.

Following are the feature's of a frog, analogus to in fish:

(a)Both frogs and fish belong to the phylum Chordata and the subphylum Vertebrata. This means that both frogs and fish have a spinal cord and backbone.

(b)Both frogs and fish are exothermic, or cold-blooded. This means that they cannot control their body temperature by internal means.

(c)Both frogs and fish usually lay eggs in water. However, both have exceptions to this rule as well. Some fish, like guppies and certain sharks give live birth instead of laying eggs. And certain toads, close relatives of frogs, give live birth as well. So most frogs and fish lay eggs in water, but a few give live birth instead.

Ques:Why are placoderms considered a "stand alone" group of gnathostomes?

Ans:Gnathostomes or “jaw-mouths” are vertebrates that possess jaws. One of the most significant developments in early vertebrate evolution was the development of the jaw, which is a hinged structure attached to the cranium that allows an animal to grasp and tear its food.

Placoderm, is any member of an extinct group of primitive jawed fishes known only from fossil remains. Placoderms existed throughout the Devonian Period (about 416 million to 359 million years ago), but only two species persisted into the succeeding Carboniferous Period. During the Devonian they were a dominant group, occurring in all continents except South America in a variety of marine and freshwater sediments.Hence, are considered "Stand Alone" Gnathostomes.