BIO 180 Lecture 15:02

found in descendants modern reptiles birds egg

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Unformatted text preview: terrestrial forms. - Found in descendants: modern reptiles, birds, egg-laying mammals. What is an Amniotic Egg and what does it do? - provides water, nutrients & mechanical support - 3 internal membranes (extra S.A. -> efficient diffusion -> *larger eggs) - leather or calcified shell. Variation in Egg-Laying Strategies 1. Oviparous * - Most fish & amphibians, all birds – why? 2. Ovoviviparous - Give birth to live young. * - Most sharks, some lizards & snakes. 3. Viviparous - Give birth to live young. * - Most mammals. Placenta - Organ rich in blood vessels that facilitates transfer of oxygen and nutrients from mother to developing offspring. - Derived from maternal and embryonic tissues (chorion, allantois) Ex. Sharks show entire range. Advantages of Viviparity & Placenta 1. 2. 3. Disadvantage? Parental Care - Parental care particularly extensive in mammals and birds. - Mammals evolved lactation – produce milk to feed offspring....
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This note was uploaded on 02/24/2014 for the course BIOL 180 taught by Professor Freeman during the Winter '07 term at University of Washington.

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