End Show Slide 1 of 41 Copyright Pearson Prentice Hall Biology

End Show Slide 2 of 41 Copyright Pearson Prentice Hall 27–1 Flatworms

End Show 27–1 Flatworms Slide 3 of 41 Copyright Pearson Prentice Hall What Is a Flatworm? What are the defining features of flatworms?

End Show 27–1 Flatworms Slide 4 of 41 Copyright Pearson Prentice Hall What Is a Flatworm? Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have three embryonic germ layers, bilateral symmetry, and cephalization.

End Show 27–1 Flatworms Slide 5 of 41 Copyright Pearson Prentice Hall What Is a Flatworm? Flatworms are acoelomates, which means they have no coelom. A coelom is a fluid-filled body cavity that is lined with tissue derived from mesoderm. The digestive cavity is the only body cavity in a flatworm. Flatworms have bilateral symmetry.

End Show 27–1 Flatworms Slide 6 of 41 Copyright Pearson Prentice Hall What Is a Flatworm? Three germ layers of a flatworm

End Show 27–1 Flatworms Slide 7 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Flatworms are thin and most of their cells are close to the external environment. All flatworms rely on diffusion for respiration, excretion, and circulation.

End Show 27–1 Flatworms Slide 8 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Free-living flatworms have organ systems for digestion, excretion, response, and reproduction. Parasitic species are typically simpler in structure than free-living flatworms.

End Show 27–1 Flatworms Slide 9 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Feeding Flatworms have a digestive cavity with a single opening through which both food and wastes pass. Near the mouth is a muscular tube called a pharynx. Flatworms extend the pharynx out of the mouth. The pharynx then pumps food into the digestive cavity.

End Show 27–1 Flatworms Slide 10 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Most parasitic worms do not need a complex digestive system. They obtain nutrients from foods that have already been digested by their host.

End Show 27–1 Flatworms Slide 11 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Respiration, Circulation, and Excretion Flatworms do not need a circulatory system to transport materials. Flatworms rely on diffusion to transport oxygen and nutrients to their internal tissues, and to remove carbon dioxide and other wastes from their bodies.

End Show 27–1 Flatworms Slide 12 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Flatworms have no gills or respiratory organs, heart, blood vessels, or blood. Some flatworms have flame cells which are specialized cells that remove excess water from the body. Flame cells may filter and remove metabolic wastes.

End Show 27–1 Flatworms Slide 13 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Response In free-living flatworms, a head encloses ganglia, or groups of nerve cells, that control the nervous system. Two long nerve cords run from the ganglia along both sides of the body.

End Show 27–1 Flatworms Slide 14 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Many free-living flatworms have eyespots. Eyespots are groups of cells that can detect changes in light. Most flatworms have specialized cells that detect external stimuli. The nervous systems of free-living flatworms allow them to gather information from their environment.

End Show 27–1 Flatworms Slide 15 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Digestive Structures of a Planarian Mouth Pharynx Digestive cavity Head Eyespot

End Show 27–1 Flatworms Slide 16 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Testes Ovary Ganglia Nerve cords Excretory system Flame cell Excretory tubule Excretory, Nervous, and Reproductive Structures of a Planarian

End Show 27–1 Flatworms Slide 17 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Movement Free-living flatworms move in two ways. Cilia on their epidermal cells help them glide through the water and over the bottom of a stream or pond. Muscle cells controlled by the nervous system allow them to twist and turn.

End Show 27–1 Flatworms Slide 18 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Reproduction Most free-living flatworms are hermaphrodites that reproduce sexually. A hermaphrodite is an individual that has both male and female reproductive organs. Two worms join in a pair and deliver sperm to each other. The eggs are laid in clusters and hatch within a few weeks.

End Show 27–1 Flatworms Slide 19 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Asexual reproduction takes place by fission, in which an organism splits in two. Each half grows new parts to become a complete organism. Parasitic flatworms often have complex life cycles that involve both sexual and asexual reproduction.

End Show 27–1 Flatworms Slide 20 of 41 Copyright Pearson Prentice Hall Groups of Flatworms What are the characteristics of the three groups of flatworms?

End Show 27–1 Flatworms Slide 21 of 41 Copyright Pearson Prentice Hall Groups of Flatworms The three main groups of flatworms are turbellarians flukes tapeworms Most turbellarians are free-living. Most other flatworm species are parasites.

End Show 27–1 Flatworms Slide 22 of 41 Copyright Pearson Prentice Hall Groups of Flatworms Turbellarians Turbellarians are free-living flatworms. Most live in marine or fresh water. Most species live in the sand or mud under stones and shells.

End Show 27–1 Flatworms Slide 23 of 41 Copyright Pearson Prentice Hall Groups of Flatworms Flukes Flukes are parasitic flatworms. Most flukes infect the internal organs of their host.

End Show 27–1 Flatworms Slide 24 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Flukes can infect the blood or organs of the host. Some flukes are external parasites. In the typical life cycle of parasitic flukes, the fluke lives in multiple hosts.

End Show 27–1 Flatworms Slide 25 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Life Cycle of a Blood Fluke

End Show 27–1 Flatworms Slide 26 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms A blood fluke’s primary host is a human. Blood flukes infect humans by burrowing through the skin. Human intestine Tailed larva

End Show 27–1 Flatworms Slide 27 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Once inside the human, they are carried to the blood vessels of the intestines. In the intestines the flukes mature and reproduce. Embryos are released and are passed out of the body with feces. Adult fluke Embryo

End Show 27–1 Flatworms Slide 28 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms If the embryos reach water, they develop into swimming larvae that infect a snail (the intermediate host). An intermediate host is an organism in which a parasite reproduces asexually. Life Cycle of a Blood Fluke Embryo Ciliated larva

End Show 27–1 Flatworms Slide 29 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Larvae that result from asexual reproduction are released from the snail into the water to begin the cycle again. Life Cycle of a Blood Fluke

End Show 27–1 Flatworms Slide 30 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Tapeworms Tapeworms are long, flat, parasitic worms that are adapted to life inside the intestines of their hosts.

End Show 27–1 Flatworms Slide 31 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Tapeworms have no digestive tract and absorb digested food directly through their body walls. The head of an adult tapeworm, called a scolex, is a structure that can contain suckers or hooks. The tapeworm uses its scolex to attach to the intestinal wall of its host.

End Show 27–1 Flatworms Slide 32 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Structures of a Tapeworm Mature proglottids Zygotes Testes Ovary Uterus Young proglottids Scolex

End Show 27–1 Flatworms Slide 33 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Proglottids are the segments that make up most of the worm's body. Mature proglottids contain both male and female reproductive organs. Sperm produced by the testes (male reproductive organs), can fertilize eggs of other tapeworms or of the same individual.

End Show 27–1 Flatworms Slide 34 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms After the eggs are fertilized, the proglottids break off and burst to release the zygotes. The zygotes are passed out of the host in feces. The eggs ingested by an intermediate host hatch and grow into larvae. Larvae burrow into the intermediate host’s muscle tissue.

End Show 27–1 Flatworms Slide 35 of 41 Copyright Pearson Prentice Hall Form and Function in Flatworms Larvae form a dormant protective stage called a cyst. If a human eats incompletely cooked meat containing these cysts, the larvae become active and grow into adult worms within the human’s intestines, beginning the cycle again.

End Show - or - Continue to: Click to Launch: Slide 36 of 41 Copyright Pearson Prentice Hall 27–1

End Show Slide 37 of 41 Copyright Pearson Prentice Hall 27–1 Flatworms are the simplest animals to have a.two germ layers. b.bilateral symmetry. c.radial symmetry. d.two openings in the digestive system.

End Show Slide 38 of 41 Copyright Pearson Prentice Hall 27–1 An individual that has both male and female reproductive organs is known as a a.turbellarian. b.proglottid. c.hermaphrodite. d.parasite.

End Show Slide 39 of 41 Copyright Pearson Prentice Hall 27–1 The function of flame cells in flatworms is to a.digest food and move it to various parts of the body. b.detect the presence of chemicals in the surroundings. c.remove excess water and metabolic wastes d.move reproductive cells into position for fertilization.

End Show Slide 40 of 41 Copyright Pearson Prentice Hall 27–1 A flatworm that lacks a digestive tract is the a.planarian. b.free-living flatworm. c.tapeworm. d.fluke.

End Show Slide 41 of 41 Copyright Pearson Prentice Hall 27–1 Turbellarians differ from most other flatworms because they a.live freely on land. b.live freely in fresh and salt water. c.are marine parasites. d.are land-dwelling parasites.

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