1. Explain How do insects, reptiles, and birds eliminate ammonia and how do mammals eliminate ammonia
Apply Concepts How do kidneys help maintain homeostasis while processing nitrogenous wastes
Review In what form do (a) annelids and mollusks, (b) insects and arachnids, (c) mammals and land amphibians, and (d) reptiles and birds excrete nitrogenous wastes
Relate Cause and Effect Explain how differing water balance needs relate to an animals conversion of ammonia to wither urea or uric acid

2. Ch 27 Animal Systems I
27.4 Excretion

3. The Ammonia Problem
Breakdown of proteins by cells releases a nitrogen- containing waste: ammonia
Ammonia is poisonous
Moderate concentrations of ammonia can kill most cells.

4. Excretion
Elimination of metabolic wastes, such as ammonia
Small animals in wet environments get rid of ammonia by allowing it to diffuse out of their body fluids across their skin
Most larger animals have excretory systems that process ammonia and eliminate it from the body.

5. Animals that cannot dispose of ammonia continuously have evolved ways to store nitrogenous wastes until they can be eliminated.

6. Storing Nitrogenous Wastes
Ammonia itself cannot be stored in body fluids because it is too toxic
Insects, reptiles, and birds convert ammonia into a sticky white compound called uric acid
Much less toxic than ammonia and is less soluble in water.

7. Mammals and some amphibians convert ammonia to urea
Urea is less toxic than ammonia
Is highly soluble in water.

8. Maintaining Water Balance
Excretory systems are extremely important in maintaining the proper balance of water in blood and body tissues
May also excrete excess water or have to conserve water.

9. Kidneys Separate wastes and excess water from blood to form urine
Pump ions from salt to create osmotic gradients
Water then “follows” those ions passively by osmosis
Usually cannot excrete excess salt.

10. Freshwater Animals
Freshwater invertebrates lose ammonia to their environment by simple diffusion across their skin.

11. Freshwater fishes and amphibians eliminate ammonia by diffusion across the same gill membranes they use for respiration.

12. Bodies of freshwater animals, such as fishes, contain a higher concentration of salt than the water they live in.

13. Water moves into their bodies by osmosis
Salt diffuses out.

14. Freshwater fish excrete lots of watery urine
Don't drink water
Actively pump salt in across their gills.

15. Saltwater Animals
Typically release ammonia by diffusion across their body surfaces or gill membranes.

16. Many marine invertebrates have body fluids with water concentrations similar to that of the seawater around them.

17. Many saltwater animals, such as fishes, contain a lower concentration of salt than the water they live in.

18. Lose water through osmosis, and salt diffuses in.

19. Saltwater fish conserve water by producing very little concentrated urine
Drink water
Actively pump salt out across their gills.

20. Excretion in Terrestrial Animals
Land animals can lose large amounts of water from respiratory membranes that must be kept moist
Must eliminate nitrogenous wastes in ways that require disposing of water.

21. Terrestrial Invertebrates
Produce urine in nephridia
Nephridia
Tubelike excretory structures that filter body fluid.

22. Terrestrial Invertebrates
Body fluid enters the nephridia through nephrostomes and becomes more concentrated as it moves along the tubes
Urine leaves the body through excretory pores.

23. Terrestrial Invertebrates
Insects and arachnids convert ammonia into uric acid
Malpighian tubules
Absorb uric acid from body fluids
Concentrate the wastes and add them to digestive wastes.

24. Water is absorbed from wastes
Crystals form a thick paste which leaves the body through the anus
Paste contains little water
Minimizes water loss.

25. Terrestrial Vertebrates
Mammals and land amphibians convert ammonia into urea
Excreted in urine by the kidneys.

26. Reptiles and birds convert ammonia into uric acid
Passed through ducts into a cavity that also receives digestive wastes from the gut
Walls of cavity absorb water
Uric acid separates as thick, milky-white paste recognized as “bird droppings.”

27. Most vertebrate kidneys cannot excrete concentrated salt
Most vertebrates cannot survive by drinking seawater
All that extra salt would overwhelm the kidneys, and the animal would die of dehydration.