BSCI 207 HW 8: Nutrients, osmoregulation and thermoregulation
1. Let’s think about how different animals adapt and adjust to control their osmolarity. Consider ONE of the
following: a sea otter (marine), a river otter (freshwater) or a dog. For the listed items, note relative
concentrations or how water and salt move. Mark with a * movement that requires energy input needed to
move salts against their concentration gradient. It is OK if you are a bit redundant between different entries.
Try to note everything that is happening.
Animal: Dog
Osmolarity relative to environment: Basically isotonic
Ingestion
Salt: Obtains salt regularly from food*
Water: Drinks water regularly
Passive transport
Water osmosis: Water is reabsorbed into the kidneys due to osmotic gradient made by salt
transport
Salt diffusion: There is small amounts of passive diffusion, most movement is actively regulated
to maintain homeostasis
Lungs
Water: Water is lost during respiration (via evaporation)
Kidneys
Water: Water is absorbed to maintain hydration and blood pressure
Salt: Salt is absorbed to maintain electrolyte balance*
Urine concentration: Moderately concentrated, varies based on hydration of dog
Urine amount: Moderate volume, lowers when dehydrated to maintain water and increases when
overhydrated
2. Countercurrent exchange is something that organisms take advantage of for a number of systems. Come
up with an example for ONE of the following systems: circulation, osmoregulation or thermoregulation.
For your example, list what is being transferred, what two fluids are moving in countercurrent directions,
and what is the advantage of setting things up this way.
System Thermoregulation
Example Blood vessels in limbs
What is being
transferred?
Heat
What is moving in
opposite directions?
Warm blood in the
arteries (coming from
body)
