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Platyhelminthes

Platyhelminthes. Flatworms. Simplest animals to have bilateral symmetry. Have 3 cell layers. Have a gut but no body cavity. Have only one opening to the gut. Respire by diffusion so they have to be flat so that all cells will have access to oxygen. Have definite organs.

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Platyhelminthes

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  1. Platyhelminthes Flatworms

  2. Simplest animals to have bilateral symmetry. • Have 3 cell layers. • Have a gut but no body cavity. • Have only one opening to the gut. • Respire by diffusion so they have to be flat so that all cells will have access to oxygen. • Have definite organs. • Exhibit cephalization. Platyhelminthes

  3. Free living flatworms The example we will use is the planaria which lives in fresh water. What do you see?

  4. They are carnivorous. • They have a muscular pharynx that acts as a vacuum cleaner to suck up food. • planaria at dinner – YouTube • Digestion begins with enzymes in the pharynx. • The partially digested food is absorbed and moved to the branching intestine. Food getting and digestion

  5. Why is the digestive system so branched? • It allows the digested food to be absorbed throughout the body. • Undigested food exits through the mouth.

  6. The cilia of flame cells beat and remove excess water and wastes from cells. • The waste is drawn into excretory tubules and exits out the excretory pores located in the planaria’s head. • Why does it need an excretory system? • It has more cells to make more wastes. Excretion of cellular wastes

  7. The gastrovascular cavity (intestine) functions in circulation by moving digested food throughout the body. • Oxygen diffuses throughout the body. • So, no blood, hearts, blood vessels or breathing organs. Circulation and Respiration

  8. The flatworms have cephalization so they contain a group of nerve tissue called ganglia at the head or anterior end. • Two nerve cords run the length of the body and are connected to each other at several points across the body. It looks like a ladder. • At the anterior end, there are light sensitive eye spots. There are also lobes that are sensitive to touch. • The nervous system also helps with movement. Nervous system

  9. A planaria has 2 layers of muscle tissue. • One is longitudinal (length wise) and the other is circular (goes around) which allow the planaria to contract, twist and turn. • The nervous system stimulates the muscles. • Cilia on the outside of the body also help with movement. Muscular System

  10. Reproduction Asexual reproduction is by binary fission or one splits into two. Planaria also have amazing powers of regeneration.

  11. Planaria are hermaphrodites. • Planaria line up and trade sperm with each other. • Fertilization is internal. • The zygote or fertilized egg is released into the water. Sexual Reproduction

  12. Tapeworms live in many hosts including cattle, pigs and fish. • The main cause of tapeworm infection in humans is eating undercooked meat from infected animals. • It is also possible to contract pork tapeworms from foods prepared by an infected person. • Can cause life threatening problems. Parasitic flatworms

  13. Tapeworms have a three stage lifecycle. • A. egg • B.larva, an immature stage • C.adult during which the worm can produce eggs. Life cycle

  14. Abdominal pain • Vomiting • Nausea • General weakness • Diarrhea • Weight loss • Altered appetite • Dizziness • Convulsions • Malnutrition Symptoms?

  15. Food, water or contaminated soil • Eating infected meat/fish • Human to human transmission • Insect to human (such as fleas) • From dogs How do I get it?

  16. Structure At the anterior end is the “head” or SCOLEX. It is knob shaped and has hooks or suckers. The main body is composed of a series of sections called PROGLOTTIDS. It adds proglottids behind its neck as it grows. They can exceed 10 feet in length.

  17. Excretory is similar to the planaria. There are flame cells which act as kidneys and excretory tubules. • Reproductive system is for sexual reproduction only. Tapeworms are hermaphroditic. Each mature proglottid has a complete male and female reproductive system. The last proglottids are gravid which means they are filled with eggs. • No circulatory, respiratory, nervous, muscular or digestive system. Systems

  18. Why is there no digestive or nervous system? • There is no need for digestion since the host does the digesting. • Also, there is not much to detect or sense inside the host. 0

  19. Q. First, what is an adaptation? • A. A trait that helps an organism survive. • Produces 10’s to 1000’s of eggs to ensure that some will survive. • Has suckers and/or hooks to attach. • Has a tough outer covering (tegument) to resist digestion by host. • Lacks certain systems so they don’t need to expend energy on these. Adaptations

  20. Flukes are another type of parasitic flatworm. • They have an intermediate host.Monsters Inside Me: The Lung Fluke : Video : Animal Planet • Rare in the United States but infect millions of people in Southeast Asia, Northern Africa and tropical areas. • Do not exceed 4 inches. Flukes

  21. Flukes do have a digestive and excretory system. They also have a nervous system. • They have an outer covering to resist digestion. • They also make 1000’s of eggs. • They are hermaphroditic. At one stage they have sexual reproduction and at another stage they have asexual. Structure

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