Digital Learning & Online Textbooks – Cengage



Key Concept Review (Answers to in-text “Concept Checks”)

Chapter 15

1. Animals are active multicellular organisms incapable of synthesizing their own food.

2. During the oxygen revolution photosynthetic autotrophs changed the composition of the atmosphere from less than 1% free oxygen to its present oxygen-rich mixture of more than 20%.

3. Heterotrophs (animals) cannot make their own oxygen and must obtain it from their surroundings.

4. A phylum is a group of animals that shares similar architecture, level of complexity, and evolutionary history.

5. Invertebrates are generally soft-bodied animals that lack a rigid internal skeleton for the attachment of muscles.

6. Suspension feeders strain plankton and tiny organic food particles from the surrounding water.

7. Cnidarians take their name from the large stinging cells called cnidoblasts, deployed on tentacles that bend or retract toward the mouth. Jellies and sea anemones are examples of cnidarians.

8. Radially symmetrical organisms are round and have no right of left sides. The bodies of bilaterally symmetrical creatures have a left side and a right side that are mirror images of each another.

9. Worms have some concentration of sensory tissue in what may be termed a head, and many have flow-through digestive systems and systems to circulate fluids and eliminate waste. They often show complex organ system integration and many have eyes.

10. Arthropods are by far the most successful of Earth’s animal phyla, occupying the greatest variety of habitats, consuming the greatest quantities of food, and existing in almost unimaginable numbers.

11. Mollusks share a common origin—possibly an ancestral segmented worm—and therefore share a few basic characteristics. All mollusk eggs develop in similar ways, and those ways differ from the embryonic development of all other phyla.

12. Gastropods include snails; bivalves include the clams and mussels; cephalopods include squid and octopuses.

13. Arthropods do not have a steady growth pattern; instead, their external growth progresses in a series of steplike jumps as the animal molts and replaces its exoskeleton. In a sense, the arthropod grows without getting bigger between these jumps in size – their flesh gets “meatier” without increasing in bulk.

14. Many echinoderms possess a unique water-vascular system, a complex of water-filled canals, valves, and projections used for locomotion and feeding.

15. The notochord is a stiffening structure (a “scaffold”) on which a complex embryo may be constructed.

16. Not all chordates have backbones. Some, like sea squirts lack this structure.

17. About 95% of chordates retain their notochord (or the vertebral column that forms from it) into adulthood. These are the familiar vertebrate chordates (fish, reptiles, birds, and mammals). Invertebrates lack this structure. All animals except vertebrate chordates are invertebrates.

18. The line to modern vertebrates probably passed through an Amphioxus-like predecessor that lived in the ocean more than 500 million years ago. Besides the backbone, vertebrate chordates differ from the invertebrate chordates by having an internal skeleton of calcified bone or cartilage (or both).

19. Listed from primitive to advanced, fish classes include the hagfishes of class Agnatha, the sharks and rays of class Chondrichthyes, and the bony fishes of the class Teleostei.

20. The largest fishes are the whale sharks of class Chondrichthyes, but the most economically important fishes are the bony fishes.

21. The great majority of fishes are cold blooded (ectothermic). The internal temperature of some of the faster-swimming fishes (tuna, for example) may rise above ambient, but their internal temperature is not as stable as that of a true endotherm.

22. Only a few sharks are dangerous to humans, and in a typical year stings by jellies kill more people than sharks. On the other hand, we’re pretty dangerous to the sharks, killing more than 100 million of them every year in commercial and recreational fishing.

23. Most actively-swimming fishes are streamlined (tear-drop shaped). Fast fishes have a scythelike tail to couple muscular energy to the water. The fish’s body can be shorter and can face more squarely in the direction of travel; so the drag losses are lower. Some species secrete a small amount of friction-reducing mucus or oil onto their surface to minimize turbulence, and some can tuck maneuvering fins into body recesses.

24. Fish take in water containing dissolved oxygen at the mouth, pump it past fine gill membranes, and exhaust it through rear-facing gill slits. The higher concentration of free oxygen dissolved in the water causes oxygen to diffuse through the gill membranes into the animal; the higher concentration of CO2 dissolved in the blood causes CO2 to diffuse through the gill membranes to the outside.

25. Schooling behavior confuses predators which can have difficulty selecting one fish from the swirling mass. Also, if fishes are clumped together, a predator must spend more time searching for lunch than if the fishes were randomly distributed within the predator’s environment.

26. Sea turtles are skilled navigators. They can return to their home beaches for decades after their initial departure.

27. Birds probably evolved from small, fast-running dinosaurs about 160 million years ago.

28. True seabirds generally avoid land unless they are breeding; they obtain virtually all their food from the sea and seek isolated areas for reproduction.

29. The 100 species of tubenoses are the world’s most oceanic birds. The largest of the tubenoses are the magnificent wandering albatrosses. The key to these birds’ success lies in their aerodynamically efficient wings. Albatrosses can cover great distances in search of food with very little expense of energy, flying continuously for weeks or months at a time.

30. Penguins have completely lost the ability to fly, but they use their reduced wings to swim for long distances and with great maneuverability. Their neutral buoyancy is an advantage as they forage for food underwater.

31. Marine mammals share a streamlined body shape, endothermy (they are warm-blooded), highly modified respiratory systems, and osmotic adaptations (they do not require an intake of fresh water).

32. Mysticete whales are the largest animals ever to have lived on Earth. They are thought to have evolved from an early line of ungulates (leading to today’s horses and sheep). Intermediate fossils outlining this progression exist.

33. Toothed whales search for prey using echolocation, the biological equivalent of sonar. The sharp clicks and other sounds they generate bounce off prey species and return to be recognized. Reflected sound is also used to build a “picture” of the animal’s environment and to avoid hitting obstacles while swimming at high speed.

34. True seals have a smooth head with no external ear flaps, the external part of the ear having been sacrificed to further streamline the body. Seals look like watermelons with a face. Sea lions, familiar to many as the performers in “seal” shows, have hind limbs with a greater range of motion and are thus more mobile on land. They have a streamlined head with small external ears.

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