Introduction to Animals Unity and Diversity of Life Q: What characteristics and traits define animals? 25.1 What is an animal? WHAT I KNOW SAMPLE ANSWER: Animals are different from other living things (bacteria, protists, fungi, and plants). WHAT I LEARNED SAMPLE ANSWER: All animals are multicellular, eukarytotic, and heterotrophic. Their cells lack cell walls. Chordates exhibit four characteristics during some stage of their development: a dorsal, hollow nerve cord; a notochord; a tail that extends beyond the anus; and pharyngeal pouches. 25.2 How have different animal body plans evolved? SAMPLE ANSWER: Each animal group evolved a group of structures or body plan that is unique to that group. SAMPLE ANSWER: The features of a body plan include levels of organization (cells, tissues, organs, organ systems); body symmetry; differentiation of germ layers; formation of a cavity between the digestive tract and the body wall; patterns of embryological development; segmentation; cephalization; and limb formation. The features of body plans provide evidence needed to build a cladogram, or phylogenetic tree, of animals. Chapter 25 Workbook A Copyright by Pearson Education, Inc., or its affiliates. All Rights Reserved. 393
25.1 What Is an Animal? Lesson Objectives List the characteristics that all animals share. Differentiate between invertebrates and chordates. List and discuss the essential functions that animals perform in order to survive. Lesson Summary Characteristics of Animals All animals are multicellular, heterotrophic, and eukaryotic. Their cells lack cell walls. Types of Animals Animals are often classified into two broad categories: invertebrates and chordates. Invertebrates do not have a backbone, or vertebral column. More than 95 percent of all animal species are invertebrates. Invertebrates are classified in at least 33 phyla, the largest taxonomic groups of animals. Examples of invertebrates are sea stars, jellyfishes, and insects. Chordates exhibit four characteristics during some stage of development: a dorsal, hollow nerve cord; a notochord; a tail that extends beyond the anus; and pharyngeal pouches. A notochord is a supporting rod that runs through the body just below the nerve cord. Pharyngeal pouches are paired structures in the throat region. Most chordates develop a backbone, or vertebral column. They are vertebrates. What Animals Do to Survive Animals must maintain homeostasis in order to survive. One important way to maintain homeostasis is feedback inhibition, also called negative feedback, in which the product or result of a process limits the process itself. In order to maintain homeostasis, animals must gather and respond to information; obtain and distribute oxygen and nutrients; collect and eliminate carbon dioxide and other wastes. They also reproduce. Characteristics of Animals 1. Complete the graphic organizer to summarize the characteristics of animals. Animals have characteristics such as Multicellular Heterotrophic Eukaryotic No cell walls 394
Types of Animals 2. Are invertebrates rare? Explain your answer. No, they are common. More than 95 percent of animal species are invertebrates. 3. What is an invertebrate? An invertebrate is an animal that lacks a backbone, or vertebral column. 4. Why do invertebrates not form a clade? They are not a clade because they are defined by the absence of a characteristic. 5. What are some examples of invertebrates? Sea stars, worms, jellyfishes, and insects are invertebrates. 6. Look at the diagram of a chordate. Write the name of the labeled structure on the lines below. a. Notochord b. Hollow nerve cord c. Tail d. Pharyngeal pouches 7. Are all chordates vertebrates? Explain your answer. No, some chordates never develop a backbone. 8. What groups of animals are vertebrates? Vertebrates include fishes, amphibians, reptiles, birds, and mammals. 9. Both snakes and earthworms have long, streamlined body shapes, but snakes are vertebrates and earthworms are not. Why are they classified differently despite their similarity in appearance? Animals are classified based on body plans, not similarity of appearance. Earthworms do not have the characteristics of a chordate, so they are considered invertebrates. 395
What Animals Do to Survive 10. Complete the graphic organizer to define three ways that animals maintain homeostasis. Animals Maintain Homeostasis by Gathering and responding to information Obtaining and distributing oxygen and nutrients Collecting and eliminating carbon dioxide and other wastes 11. The diagram on the left below shows the feedback inhibition that maintains temperature in a house. Complete the blank boxes in the diagram on the right below to show how body temperature is maintained in a human being. Thermostat turns furnace off. Thermostat turns furnace on. Sweating cools body. Shivering. Muscle activity generates heat. House gets cold. House gets hot. Body gets cold. Body gets hot. 12. Describe generally how an animal s nervous and musculoskeletal systems work together to allow it to escape a predator. The animal s sensory receptors, which are part of the nervous system, sense a predator. Its nervous system then sends signals to the musculoskeletal system to flee. The animal s muscles work with its skeleton to allow it to move away from the predator. 13. In complex animals, what system collects metabolic wastes and delivers them to the respiratory and excretory systems? the circulatory system 14. In complex animals, which three body systems work together to obtain and distribute oxygen and nutrients? the respiratory, digestive, and circulatory systems 396
For Questions 15 24, write the letter of the correct answer on the line at the left. D 15. What system gathers information through receptors for sound, light, chemicals, and other stimuli? A. respiratory B. circulatory C. musculoskeletal D. nervous C B B A D D 16. Most chordates have a large number of nerve cells concentrated into a A. backbone. B. notochord. C. brain. D. pharyngeal pouch. 17. How does muscle tissue generate force? A. It stretches. B. It shortens. C. It inflates. D. It dilates. 18. How do the skeletons of insects and vertebrates differ? A. Insects have fluid skeletons. Vertebrates have external skeletons. B. Insects have external skeletons. Vertebrates have internal skeletons. C. Insects have internal skeletons. Vertebrates have external skeletons. D. Insects have external skeletons. Vertebrates have fluid skeletons. 19. What process allows some aquatic animals to breathe through their skin? A. diffusion B. digestion C. excretion D. circulation 20. Which structure performs a function most similar to that of gills? A. heart B. intestine C. blood vessel D. lung 21. Which of these functions requires the coordinated actions of the digestive, circulatory, and excretory systems? A. gathering O 2 and distributing it to body systems B. collecting and eliminating CO 2 from tissues C. acquiring nutrients and distributing them to body systems D. collecting and eliminating metabolic wastes 397
A C B 22. How do the respiratory system and excretory system differ in the wastes they eliminate? A. The respiratory system eliminates carbon dioxide. The excretory system eliminates ammonia. B. The respiratory system eliminates wastes that contain nitrogen. The excretory system eliminates carbon-based wastes. C. The respiratory system eliminates oxygen and nitrogen. The excretory system eliminates ammonia. D. The respiratory system eliminates ammonia. The excretory system eliminates carbon dioxide. 23. Which activity is required for survival of the species but not survival of the organism? A. digestion B. excretion C. reproduction D. circulation 24. What is an advantage of asexual reproduction? A. It increases genetic diversity in a population. B. It produces large numbers of offspring rapidly. C. It increases a species ability to evolve. D. It produces offspring that are genetically different from the parents. 25. In what ways do invertebrates differ from vertebrates? Identify at least three groups of invertebrates. SAMPLE ANSWER: Invertebrates have no backbones. They don t have a nerve cord, a notochord, a tail, or pharyngeal pouches. Invertebrate groups include insects, worms, sea stars, and jellyfishes. 26. Suppose you were studying the cell walls of a multicellular organism under a microscope. Were you studying an animal? Explain your answer. No, it wasn t an animal, because animal cells have no cell walls. 398