Download 049539193X_177846

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,
1|Page
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.
2|Page
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 warmblooded), 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.
3|Page