1. Excretion
AP Biology
Unit 6

2. Osmolarity
Osmolarity = moles of osmotically active particles per liter of solvent
1 M Glucose = 1 Osmolar solution
1 M NaCl = 2 Osmolar solution
2 osmotically active particles because NaCl dissociates to become Na+ and Cl- in water
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3. Question…
What would happen if your body did not maintain proper osmolarity?
You would either have an excess of water (bloated) or too little water (dehydrated)
Cells wouldn’t have the correct balance of solutes and H2O  won’t function properly
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4. Osmoconformers
Animals whose internal osmolarity changes in relation to their external environment
Equilibrate with the environment
There are limits to this– too high or too low will cause death
Marine invertebrates
Ex. Brine Shrimp (Artemia)
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5. Osmoregulators
Animals who can maintain their internal osmolarity at a particular level regardless of the external environment
Ex. Fish, humans, lots of other animals 
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6. Question…
How does the environment one lives in affect how osmoregulation takes place?
Depending on the environment one lives in, osmoregulation can be very different
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7. Saltwater Fish
Challenge: Prevent too much water from leaving the body (to go into the outside environment)
Higher osmolarity outside compared to inside of body
Solution…
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8. Freshwater Fish
Challenge: Prevent too much water from coming into the body from the outside
Higher osmolarity inside body compared to outside
Solution…
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9. Birds: Salt Glands
Many birds who live by the sea may take in sea water along with the food they eat
They get rid of the extra salt in their bodies by excreting it through nasal salt glands  sneeze or shake off the salt droplets
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10. Nitrogen Waste
Nitrogenous wastes are a type of metabolic waste that must be removed from the body.
Carbohydrates broken down into CO2 and H2O
Fats broken down into CO2 and H2O
Proteins and Nucleic Acids broken down into NH2 groups (urea, ammonia, uric acid)
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11. continuously excreted (keep internal levels low) OR
Ammonia
Ammonia is the most common nitrogen waste
Toxic at certain concentrations
To prevent toxicity to the animal ammonia must be
continuously excreted (keep internal levels low) OR
Converted to a nontoxic molecule (urea or uric acid) before excretion
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12. Excretion in Aquatic Animals
For most aquatic animals, excreting ammonia is not an issue - why?
Ammonia is highly soluble in H2O, diffuses away rapidly (won’t stay concentrated around them)
Aquatic animals continuously lose ammonia from their bodies through diffusion across their gill membranes
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13. Ammonotelic
Animals that excrete nitrogen waste mostly as ammonia are ammonotelic
Ex. Aquatic invertebrates, bony fish
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14. Question…
Why don’t terrestrial animals and some aquatic animals just excrete dilute ammonia in liquid?
Since ammonia is toxic even at fairly low levels, it would have to use a lot of water to dilute it
Too much water loss = dehydration
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15. Ureotelic
Animals that excrete nitrogen waste mostly as urea are ureotelic
Ex. Mammals (us!), amphibians, sharks, rays, some bony fish
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16. Uricotelic
Animals that excrete nitrogen waste mostly as uric acid are uricotelic
Helps conserve H2O because it isn’t very soluble in water  semi solid
Ex. Birds, reptiles, insects, some amphibians
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17. Excretory Process The main steps in producing urine (fluid waste) are:
Filtration
Selective Reabsorption
Secretion
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18. Filtration
nonselective process in which water and small solutes are filtered across a membrane into the excretory system
Small solutes include salts, nitrogen wastes, sugars, amino acids
Filtrate is the liquid produced from this step
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19. Selective Reabsorption
Useful/”good” molecules are reabsorbed back into the body from the excretory system
Sugars, amino acids, some salts,
By active transport
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20. Secretion
More waste (toxins, extra salts, etc) are transported into the filtrate
By active transport
Selective reabsorption and secretion also causes water to move in /out of filtrate
Urine = whatever is left of the filtrate after it has completed all 3 steps
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21. Protonephridia Excretory system found in flatworms (platyhelminthes)
Consists of a series of tubules that dead end in the body, open up to nephridiopores on the side of body
Dead ends contain flame cells
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22. Protonephridia
The cilia in the flame cells cause water and solutes to enter from the interstitial fluid
The beating of the cilia causes the filtrate to flow down the tubule towards the nephridiopore
As the filtrate flows, it is modified (water, solutes reabsorbed)
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23. Metanephridia Excretory system found in earthworms (annelids)
Each segment of the worm has 2 metanephridia in it
Due to pressure from blood (closed circulatory system), water and solutes are pushed from the blood into the coelomic fluid
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24. Metanephridia
Coelomic fluid enters the metanephridia at an opening called the nephrostome
As the fluid passes through the metanephridia, it is altered (water, solutes, reabsorbed)
Urine is excreted through the nephridiopore
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25. Malpighian Tubules Excretory system in insects
tubules attached to the midgut and hindgut of digestive system
Open circulatory system doesn’t allow insects to produce filtrate through filtration
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26. Malpighian Tubules
Uric acid, and ions (Na+ and K+) are actively transported into the Malpighian tubules  H2O follows by osmosis
Na+ and K+ are actively transported back into coelom from hindgut
Uric acid precipitates out of solution  H2O returns to coelom (by osmosis), uric acid is excreted
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