1. Controlling the Internal Environment II: Salt and water balance

2. Keywords (reading p. 879-884) Ammonia toxicity Urea Uric acid
Osmoconformer
Osmoregulator
Passive transport
Facilitated diffusion
Active transport
Uniport
Antiport
symport
Osmoregulation by an aquatic invertebrate
Osmoregulation in marine fish
Osmoregulation in freshwater fish
Water loss on land
Permeable and impermeable body surfaces
Kangaroo rate water balance
anhydrobiosis

3. The internal environment
In most animals, the majority of cells are bathed by internal fluids rather than the environment
This is advantageous since there can be control of substrates needed for metabolism

4. Consider the origin of life: started out as enzymes in the primordial sea

5. Rates of reactions were determined by the concentrations of substrates in the environment

6. The first proto-organism enclosed it’s enzymes inside a membrane and became a cell

7. Control of substrate concentration Products do not diffuse away

8. Good because you can keep out molecules that you don’t want
Good because reactions will work better and you don’t lose the products
Good because you can keep out molecules that you don’t want
Bad because there can be osmotic problems
Bad because hazardous by products can stay in the cell
Hazardous products

9. Therefore the internal chemical environment is controlled
A. Avoiding buildup of toxic chemicals
Dealing with ammonia
B. Osmoregulation - controlling internal solutes

10. A. Avoiding buildup of toxic chemicals

11. Hazardous products
A major source of hazardous products is the production of nitrogenous wastes
Ammonia (NH3) is a small and very toxic molecule that is normal product of protein and amino acid breakdown
If you are an aquatic organism, ammonia can readily diffuse out of the body and this is not a problem

13. Ammonia toxicity is a problem for terrestrial animals
Ammonia does not readily diffuse away into the air.
The strategy of terrestrial animals is to detoxify it then get rid of (excrete) it.

14. Ammonia can be converted to urea which is 100,000 times less toxic
Mammals, most amphibians, sharks, some body fishes

15. The drawback of using urea
Takes energy to synthesize
Still need to use water to “flush it out”

16. Some animals cannot afford to use water to excrete urea
These animals use excrete uric acid instead

17. Since uric acid is not very soluble in water, it can be excreted as a paste.
Less water is lost
Disadvantages:
Even more costly to synthesize.
Loss of carbon
Uric acid

18. Who uses uric acid? Birds, insects, many reptiles, land snails
Related to water use, but also reproduction
Eggs - N wastes from embryo would accumulate around it if ammonia or urea are used. Uric acid precipitates out.

19. B. Osmoregulation - controlling internal solutes

20. Osmolarity Osmolarity = # of solutes per volume solution
Often expressed in moles (6.02 x 1023 atoms/molecules) per liter.
1 mole of glucose = 1 mole of solute
1 mole of NaCl = 2 moles of solute

21. Osmotic problems
Humans have internal solute concentration (osmolarity) of 300 milliosmoles per liter (mosm/L)
The ocean is 1000 mosm/L

22. What would happen if your body surface is water permeable and you fall into the sea
1000 mosm/L
Keep your internal concentrations the same as the environment (osmoconformer)
Regulate your internal concentrations (osmoregulator)
300 mosm/L

23. Jellyfish in the ocean 1000 mosm/L 1000 mosm/L
Keep solutes at 1000 mosm/L no water loss or gain.
A relatively simple solution
1000 mosm/L
1000 mosm/L
jellyfish

24. Life in freshwater - hydra living in a pond
Can the same strategy of matching the environmental osmolarity be used?
0 mosm/L
0 mosm/L
Green hydra

25. Hydra living in a pond
If external osmolarity is very low like 0 mosm/L, hydra cannot maintain an internal osmolarity of 0 mosm/L
Why is this?
Consequently freshwater animals will most likely have a higher osmolarity than the environment.

26. What happens to freshwater organisms?
Water from the environment is continually entering tissues.
The diffusion gradient favors loss of solutes
Therefore there is a need to regulate solutes and water

27. Two ways to deal with osmotic problems
Keep your internal concentrations the same as the environment (osmoconformer)
Regulate your internal concentrations (osmoregulator)

28. Solute regulation Transport solutes across the body surface
Note: even in the jellyfish example, there is ion regulation. Although the internal fluids have the same osmolarity as seawater, they do not have the same composition

29. Ways molecules get across membranes

30. Passive transport: Diffusion
Works for lipid soluble molecules and gases
No good for most water soluble molecules and ions

31. Passive transport: Facilitated diffusion
Generally used for ions, larger molecules, non-lipid soluble molecules.
Must be a gradient favoring diffusion

32. Active transport
Works for ions and molecules like glucose or amino acids
Can transport against a gradient.
Costs energy, usually ATP

33. In this diagram, how might sodium get across the membrane?
A) diffusion
B) active transport
C) facilitated diffusion or active transport
Na+
Na+
Na+
Na+

34. In this diagram, how might sodium get across the membrane?
A) diffusion
B) active transport
C) facilitated diffusion or active transport
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+
Na+

35. In this diagram, how might sodium get across the membrane?
A) diffusion
B) active transport
C) facilitated diffusion or active transport
Na+
Na+
Na+
Na+
Na+
Na+

36. In this diagram, how might steroids get across the membrane?
A) diffusion
B) active transport
C) facilitated diffusion
D) all of the above
steroid
steroid
steroid
steroid
steroid

37. In this diagram, how might steroids get across the membrane?
A) diffusion
B) active transport
C) facilitated diffusion
D) all of the above
steroid
steroid
steroid
steroid
steroid
steroid
steroid
steroid
steroid
steroid
steroid
steroid
steroid
steroid
steroid

38. Types of active transport

39. What type of active transport is this?
A) uniport
B) symport
C) antiport K+

40. What type of active transport is this?
A) uniport
B) symport
C) antiport K+
Sodium potassium ATPase
Na+

41. What type of active transport is this?
Cl-
A) uniport
B) symport
C) antiport K+

42. Responses of soft-bodied invertebrates to changes in salinity
Marine invertebrates can often be exposed to salinity changes (e.g., tidepool drying out, estuaries)
If salts enter the body, pump them out using transporters
If salts are leaving body, take them up from the environment using transporters
Or just let your internal concentrations follow changes in the environment

43. Dumping/pumping amino acids
One way to respond while keeping internal ion concentrations the same is to pump amino acids out.
Often used by bivalves living in estuaries
Clams, oysters, mussels

44. Estuary - high tide
1000 mosm/L
1000 mosm/L aa aa aa aa aa aa aa aa

45. Estuary - low tide
500 mosm/L
1000 mosm/L aa aa aa aa aa aa aa aa

46. Estuary - low tide
500 mosm/L
500 mosm/L aa aa aa aa aa aa aa aa

47. Advantages of amino acid osmoregulation
Changing amino acid concentrations is less disruptive on internal processes (enzyme function).
Costs: pumping amino acids (can involve ATP), loss of amino acids (carbon and nitrogen)

48. Osmoregulation in other aquatic organisms
Example: fishes maintain internal concentration of solutes
Body volume does not change
Involves energetic cost of active transport
In bony fishes this can be 5% of metabolic rate

49. Marine fishes

50. Marine fishes Problem: lower internal osmolarity than seawater
Water will leave body, sea salts will go in
Solution: Fish drink large amounts of seawater, then transport out ions (Na+, Cl-) at their gill surface or in urine (Ca++, Mg++, SO4--).

51. Freshwater fishes

52. Freshwater fishes
The opposite situation: tendency to lose solutes and gain water
Solutions: take up salts in food and by active transport across gills
Eliminate water via copious dilute urine production

53. Water balance on land
Unlike aquatic animals, terrestrial animals don’t lose or gain water by osmosis
However, water loss or solute gain can be a major problem
Cells are maintained at around 300 mosm/L
Humans die if they lose 12% of their body water

54. Why not just prohibit water loss?
Impermeable surfaces: waxy exoskeleton (insects), shells of land snails, thick skin (vertebrates).
Not all surfaces can be impermeable because gas exchange must also occur.
Evaporation across respiratory surfaces is only one of the two main causes of water loss
The other is urine production

55. Drinking Replenishes water that is lost
Water can also be gained by moist foods
What if there is no water to drink?

56. Desert kangaroo rat

57. Desert kangaroo rat does not drink
Don’t lose much water
Special nasal passages
Urine doesn’t contain much water
Recovers almost all of the water that results from cellular respiration

58. Note comparison is relative not absolute
Greater proportion of water intake of K rat is from metabolism

59. Low proportion of K rat water loss is in urine

60. Anhydrobiosis: Tardigrades (water bears)
Can lose 95% of their body water