BIOL 111 Lecture Notes - Lecture 23: Yolk Sac, Amniote, Allantois

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23 Jul 2016
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BIOL 111 Organismal Biology
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o!it is permeable to gas (can facilitate gas exchange)
o!it is fairly impermeable to water
!it is self-sufficient (it doesn’t need parental care)
o!however, some do need to be incubated if they are endotherms
!the amniotic egg is composed of:
o!an external shell
o!the embryo
o!extra-embryonic membranesformed by embryo during development
!yolk sac provide nutrients (sac comes from embryo, but nutrients come
from mother)
!amnionsac that surrounds the embryo and provides protection
!chorionlayer under the shell that facilitates gas exchange
!allantoiswaste sac
!albumenprovides proteins and fats
!having a terrestrial egg requires internal fertilization (sperm cannot penetrate external
shell)
o!shell and albumen are added to the fertilized egg in the female’s oviduct
o!having a terrestrial egg also requires a non-toxic nitrogenous waste (uric acid)
Excretory System
!excretory products are substances released by the body
o!nitrogenous wastes are products of DNA and protein metabolism
!they are released by the excretory organs (kidneys) as well as skin and
gills
o!carbon dioxide is waste of cellular respiration
!it is released by respiratory surfaces
o!salts and ions
!they are released by kidneys, skin and gills
o!water can also be a waste
!nitrogenous wastes:
o!ammonia (NH3)
!very soluble in water
!very toxic
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BIOL 111 Organismal Biology
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!needs to be diluted and disposed of quickly or converted to less toxic
form (urea or uric acid)
!excreted mostly by bony fishes, aquatic invertebrates, and larval
amphibians
o!urea (H2NCONH2)
!soluble in water
!not toxic
!less water needed for disposal
!excreted mostly by cartilaginous fishes, adult amphibians and mammals
o!uric acid
!insoluble in water
!not toxic
!little water needed for disposal
!excreted mainly by insects, reptiles and birds
!water balance:
o!animals in freshwater are hypertonic to environment so water readily diffuses
into the animal (this organism will constantly need to urinate)
o!organisms in marine environments are hypotonic to the environment and so water
is frequently diffusing out of the organism (they will always drink and have a
very concentrate urine)
o!osmoregulators maintain a constant concentration of ions in body fluids while
environment may change
o!osmoconformers allow ionic concentration in the body match ionic
concentration of environment
!osmoconformers only exist in marine environments, because solute level
is too low for survival if animal conformed
!e.g. marine cartilaginous fishes and marine invertebrates
!the excretory structure of flatworms is made up of flame cells and tubules (collectively
called protonephridia)
o!beating of cilia in flame cells causes fluid to enter tubules and to flow through
tubules and leave via excretory pore
!in annelids, fluid in coelom enters ciliated openings in tubules and capillaries reabsorb
wanted solutes, so that waste are excreted in every segment through nephridiopores
!insects have tubes coming off the hindgut called, Malpighian tubules
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