Excretion AP Biology Unit 6

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

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

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

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

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

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

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

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

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

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 Slide 11 of 26

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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