Using your vocabulary words, make notecards/flashcards that you can use outside of class to study.
Work on your Directed Reading in class every chance you get. Remember that I will assist you on the harder questions. This assignment is due the day we take the test on this chapter. Use the information in this assignment as a study guide for your test.
This study guide is to help you study for your test. It should not be the only item you use to study w hen preparing for the test. Remember to complete your Directed Reading for every chapter along with writing your vocabulary words on notecards to help you remember them. And always remember to listen carefully in lecture because all of the information in this study guide will be covered.
Introduction to Animals
The sponges and coral in the photograph are sessile—that is, they attach themselves to an object and remain in that place all their lives. Sponges create water currents that flow through their bodies and trap microorganisms found in these currents for food. Corals capture prey that swim within their reach.
* What are the advantages of being a sessile animal?
* Sponges were once classified as plants. Why do you think this was so?
An elephant, a hummingbird, and a jellyfish differ greatly intheir size, shape, and behavior. Nevertheless, they are all animals. In distinguishing between types of organisms, the characteristics animals have in common far outweigh the differencesamong them. However, differences in body structure are usefulin classifying animals. The arrangement of body parts is related to how a particular animal species meets the challengesof living, which include gathering food, protecting itself, andreproducing.
Symmetry and Body Plans
The arrangement of an animal's body parts determines its symmetry. Most animals are symmetrical in some way. Only a fewanimals can be described as asymmetrical, or having an arrangement of body parts that cannot be divided into correspondingsections. Many sponges are asymmetrical. They grow in variedand irregular shapes.
The symmetry of an animal generally provides a clue to itsway of life. An organism with a round form—with no front orback, no right or left side—shows spherical symmetry . Thisform is well suited to certain protozoa that roll and float inwater. Such organisms face all directions at once.
Animals whose body parts are arranged around a centralpoint, like spokes around the hub of a wheel, exhibit radialsymmetry.Their sensory organs are located around the circumference of the body. Jellyfish and sea anemones show radialsymmetry. Such animals do not move efficiently. Either theyare sessile, or they float in the water or crawl along the bottomof the sea.
Most animal species have bilateral symmetry—that is,one-half of the body is a mirror image of the other half. A butterfly is a good example of bilateral symmetry. If a line were drawnlengthwise through the butterfly's body—the longitudinalaxis—the right half would appear to be the exact opposite of theleft half.
Bilaterally symmetrical animals have upper and lower surfaces, and front and hind ends. The upper surface is called thedorsalsurface, and the lower surface the ventral surface. Thefront is the anterior end, and the hind the posterior end. For example, the backbone of a dog is dorsal, and the stomach isventral. The head is at the anterior end, and the tail is at the posterior end.
Animals that have a definite anterior end and move headfirst generally exhibit cephalization (sehf uh lih ZAY shuhn). Cephalization is an adaptation in which the neural and sensoryorgans are concentrated in the anterior end in animals. Whensuch animals move, their sensory organs go first, providinginformation about the environment that lies ahead ofthe animals.
Vertebrates and Invertebrates
Scientists make a major distinction between vertebrates, animals with a backbone or a spine, and invertebrates, animals without a backbone. Humans and other mammals are vertebrates, as are fish, amphibians, reptiles, and birds. Vertebratesare included in the phylum Chordata. Although they are themost widely recognized and familiar of all animals, vertebratesmake up only about 3 percent of the more than 1 million speciesof animals. Vertebrates are categorized by bilateral symmetryand cephalization.
About 97 percent of the animal kingdom are invertebrates.Invertebrates include sponges, jellyfish, starfish, worms, mollusks, insects, and crabs. Some species of invertebrates haveradial symmetry, and some bilateral. Some, but not all, speciesare characterized by cephalization.
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