Intro Biology BIS 001B
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This 1 page Study Guide was uploaded by Charity Daniel on Tuesday September 8, 2015. The Study Guide belongs to BIS 001B at University of California - Davis taught by Staff in Fall. Since its upload, it has received 21 views. For similar materials see /class/187637/bis-001b-university-of-california-davis in Biological Sciences at University of California - Davis.
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Date Created: 09/08/15
BIS 1B Winter 2008 Study questions Platyhelminthes lecture 11 1 Why are turbellarian atworms considered to be a paraphyletic group Turbellarian atworms represent the least modi ed of the Platyhelminthes They are free living atworms with a well developed digestive system and a typical cellular mononucleate tegument The parasitic Platyhelminthes flukes and tapeworms evidently evolved within the Turbellaria by further modification By excluding them from the Turbellaria we make Turbellaria paraphyletic In other words some Turbellaria are more closely related to flukes than they are to other turbellarians 2 Why does the tegument of tapeworms bear many tiny folds Tapeworms have no mouth or gut All feeding is done by absorbing nutrients directly across the body wall The many tiny folds microvilli of the tegument have the effect of greatly increasing the surface area available for nutrient absorption 3 Why don t you expect to see a member of the phylum Platyhelminthes that is one meter long and 10 centimeters thick F latworms have no special organs for gas exchange and all gas exchange occurs across the body wall Thus they must maintain a high surface area to volume ratio such that all metabolically active tissues are very close to the body wall within approximately 1 millimeter A length of meter is not in itselfprohibitive remember some tapeworms grow to 20 meters in length but a thickness of 0 centimeters would be a problem 4 Give an example of a complex life cycle in a platyhelminth The digenetic ukes Trematoda and tapeworms Cestoda both have complex life cycles with usually two or more hosts In T rematoda sexual reproduction occurs in a vertebrate host The fertilized eggs are released in body wastes and these develop into ciliated larvae miracidia which disperse through water to an intermediate host such as a snail Several asexual generations ensue miracidia transform into sporocysts which in turn produce rediae which in turn produce cercariae The free swimming cercariae leave the intermediate host and contact and penetrate the vertebrate host or they enter a second intermediate host where they encyst as metacercariae These must then be eaten by the definitive vertebrate host for the cycle to continue
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