Controlling the Internal Environment II: Salt and water balance
Keywords (reading p. 879-884)
The internal environment
Consider the origin of life: started out as enzymes in the primordial sea
Rates of reactions were determined by the concentrations of substrates in the environment
The first proto-organism enclosed itís enzymes inside a membrane and became a cell
Control of substrate concentration Products do not diffuse away
Good because reactions will work better and you donít lose the products
Therefore the internal chemical environment is controlled
A. Avoiding buildup of toxic chemicals
Hazardous products
PPT Slide
Ammonia toxicity is a problem for terrestrial animals
Ammonia can be converted to urea which is 100,000 times less toxic
The drawback of using urea
Some animals cannot afford to use water to excrete urea
Uric acid
Who uses uric acid?
B. Osmoregulation - controlling internal solutes
Osmolarity
Osmotic problems
What would happen if your body surface is water permeable and you fall into the sea
Jellyfish in the ocean
Life in freshwater - hydra living in a pond
Hydra living in a pond
What happens to freshwater organisms?
Two ways to deal with osmotic problems
Solute regulation
Ways molecules get across membranes
Passive transport: Diffusion
Passive transport: Facilitated diffusion
Active transport
In this diagram, how might sodium get across the membrane?
In this diagram, how might steroids get across the membrane?
Types of active transport
What type of active transport is this?
Responses of soft-bodied invertebrates to changes in salinity
Dumping/pumping amino acids
Estuary - high tide
Estuary - low tide
Advantages of amino acid osmoregulation
Osmoregulation in other aquatic organisms
Marine fishes
Freshwater fishes
Water balance on land
Why not just prohibit water loss?
Drinking
Desert kangaroo rat
Desert kangaroo rat does not drink
Note comparison is relative not absolute
Low proportion of K rat water loss is in urine
Anhydrobiosis: Tardigrades (water bears)
Email: rlee@mail.wsu.edu
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