Excretion

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 Slide 2 of 26

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 Slide 3 of 26

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) Slide 4 of 26

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 Slide 5 of 26

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 Slide 6 of 26

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… Slide 7 of 26

8. Freshwater Fish • Challenge: Prevent too much water from coming into the body from the outside • Higher osmolarity inside body compared to outside • Solution… Slide 8 of 26

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 Slide 9 of 26

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) Slide 10 of 26

11. 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 Slide 11 of 26

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 Slide 12 of 26

13. Ammonotelic • Animals that excrete nitrogen waste mostly as ammonia are ammonotelic • Ex. Aquatic invertebrates, bony fish Slide 13 of 26

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 Slide 14 of 26

15. Ureotelic • Animals that excrete nitrogen waste mostly as urea are ureotelic • Ex. Mammals (us!), amphibians, sharks, rays, some bony fish Slide 15 of 26

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 Slide 16 of 26

17. Excretory Process • The main steps in producing urine (fluid waste) are: • Filtration • Selective Reabsorption • Secretion Slide 17 of 26

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 Slide 18 of 26

19. Selective Reabsorption • Useful/”good” molecules are reabsorbed back into the body from the excretory system • Sugars, amino acids, some salts, • By active transport Slide 19 of 26

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 Slide 20 of 26

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 Slide 21 of 26

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) Slide 22 of 26

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 Slide 23 of 26

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 Slide 24 of 26

25. Malpighian Tubules • Excretory system in insects • 100 - 200 tubules attached to the midgut and hindgut of digestive system • Open circulatory system doesn’t allow insects to produce filtrate through filtration Slide 25 of 26

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 Slide 26 of 26