ExcretionExcretion

AP BiologyUnit 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

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

Protonephridia1. The cilia in the flame cells

cause water and solutes to enter from the interstitial fluid

2. The beating of the cilia causes the filtrate to flow down the tubule towards the nephridiopore

3. 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

1. Coelomic fluid enters the metanephridia at an opening called the nephrostome

2. As the fluid passes through the metanephridia, it is altered (water, solutes, reabsorbed)

3. 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

1. Uric acid, and ions (Na+ and K+) are actively transported into the Malpighian tubules H2O follows by osmosis

2. Na+ and K+ are actively transported back into coelom from hindgut

3. Uric acid precipitates out of solution H2O returns to coelom (by osmosis), uric acid is excreted

Slide 26 of 26