Chapter 14 Animal water + electrolyte balance Flashcards
Explain why water is essential to proper body function, and explain why too much
water can be a bad thing.
Essential: Physiological systems of animals operate within a fluid environment (i.e., all the chemical reactions in our body that make life possible occur in aqueous solutions).
Water intoxication occurs when a person drinks so much water that nutrients in the body become diluted to the point that they can no longer “do their jobs”.
The moral of the story: the relative concentrations of water and solutes must be maintained within narrow limits.
• If the water and solute balance in our bodies is disturbed or pushed outside those limits, chemical reactions in our body may stop – along with our lives.
Define “osmoregulation”. Define “osmotic stress”.
–> Osmoregulation: the process by which animals control
solute concentrations and balance water gain and loss.
–> Osmotic stress occurs when water and solute concentrations are
different from their set point (i.e. are abnormal).
State how excretion of metabolic wastes is functionally linked to osmoregulation.
• Animals must also deal with potentially hazardous metabolic wastes (esp. ammonia). • Several different mechanisms have evolved for excretion – the process that rids the body of nitrogenous and other metabolic wastes.
It is because it is a mechanism used to get rid of solutes and maintain water balance
Define “electrolyte”.
compounds that dissociates into ions when dissolved in water.
List 4 ways that animals gain water and 4 ways that animals lose water.
– How do animals gain water?
1. Absorbing it via osmosis
2. Drinking
3. Eating
4. By-product of cellular respiration
• How do animals lose water?
1. In urine
2. In feces
3. Via evaporation (panting, sweating, from moist surfaces)
4. Via osmotic loss
Compare and contrast an osmoconformer to an osmoregulator.
- Be an osmoconformer - be isotonic with your surroundings.
• Do not actively regulate the osmolarity of their tissues.
• Do regulate the composition of solutes inside their tissues.
• Even an animal that conforms to the osmolarity of its surroundings does regulate its internal composition to maintain homeostasis.
• Most marine invertebrates, including sponges, jellyfish, and flatworms. - Be an osmoregulator - expend energy to control the osmolarity of body fluids that are not isotonic with the outside environment.
• Must discharge excess water if it lives in a hypotonic environment or take in water if it inhabits a hypertonic environment.
• Must also actively control concentration and composition of solutes.
Describe the water and electrolyte challenges faced by organisms in different environments.
Tissues are hypotonic to surrounding environment.
Challenge: Tend to lose water and gain electrolytes.
Tissues are hypertonic to surrounding environment.
Challenge:Tend to gain water and lose electrolytes.
In hot terrestrial environments
Challenge:Risk of dehydration due to evaporation ofwater.
Explain how the osmoregulatory problems of freshwater animals differ from those of marine animals.
The body fluids of freshwater animals must be hyperosmotic because animal cells cannot tolerate salt concentrations as low as those of lake or river water. where as in marine environments they must maintime hypotonic because their is to much salt in the water
Explain why osmoregulation has an energy cost.
Diffusion tends to equalize concentrations in a system must expend energy to maintain the osmotic gradients that move water in and out.
• NOTE: Water is not actively transported.
• Animals use active transport to manipulate solute concentrations in their body fluids –> creates osmotic gradients that cause water to flow in or out.
The energy costs of osmoregulation depends on:
• How different an animal’s osmolarity is from its surroundings,
• How easily water and solutes can move across an animal’s body surface
• How much membrane transport work is required to pump solutes.
• Example: Osmoregulation accounts for 5% of the BMR of many marine and freshwater bony fishes, but 30% of BMR of brine shrimp.
• Minimizing the osmotic difference between the body fluids and the surrounding environment –> the energetic cost of osmoregulation.
• Consequently, animals that live in freshwater tend to have lower solute concentrations in their body fluids than their closest relatives that live in salt water.
Explain what is it about nitrogenous waste that makes it difficult for most animals to deal with.
- Most metabolic wastes must be dissolved in water when they are removed from the body –> impacts water balance.
- When proteins and nucleic acids are broken down for energy or converted to other organic products, enzymes remove nitrogen in the form of ammonia (NH3)
- Readily forms NH4+ = small and very toxic molecule.
- Some animals excrete ammonia directly, but many species first convert ammonia to other compounds that are less toxic, but more costly to produce.
Ammonia, which animals, why its adaptive for particular group and the main advantages and disadvantages
- Can only be tolerated at very low concentrations therefore animals that excrete ammonia need access to lots of water!
- Most common in aquatic species.
- Advantage: Energetically cheap.
Urea which animals, why its adaptive for particular group and the main advantages and disadvantages
• Because ammonia is so toxic, it can be transported and excreted only in large volumes of very dilute solutions –> not suitable for most terrestrial animals and many marine organisms.
• Mammals, most adult amphibians, sharks, and some marine bony fishes and turtles excrete urea.
• Synthesized in the liver by combining ammonia + CO2
and is excreted by the kidneys.
• Main advantage = low toxicity. Can be transported in the circulatory system and stored safely at high concentrations –> reduces the amount of water needed for nitrogen excretion.
• Main disadvantage = must expend energy to produce it from ammonia.
Uric acid which animals, why its adaptive for particular group and the main advantages and disadvantages
- Land snails, insects, birds, and many reptiles excrete uric acid as the main nitrogenous waste.
- Advantages:
- Relatively nontoxic.
- Largely insoluble in water - can be excreted as a semisolid paste with even less water loss than urea –> good option for arid environments.
- Can be stored within a shelled egg as a harmless solid.
- Soluble wastes (e.g., urea) can diffuse out of a shell-less amphibian egg or be carried away by the mother’s blood in a mammalian embryo.
- Shelled eggs of birds and reptiles are not permeable to liquids - soluble nitrogenous wastes trapped within the egg could accumulate to dangerous levels (even urea!).
- Disadvantage: Even more energetically expensive to produce!
Compare the three nitrogenous waste products in regards to energetic and water costs.
Ammonia: energetically cheap, LOTS OF WATER
Urea: Uses energy, reduced amount of water needed
Uric Acid: Expensive on energy, less water
• Amount of water required:
Ammonia > Urea > Uric acid
• Amount of energy required:
Ammonia < Urea < Uric acid
Explain the osmolarity of a shark relative to its environment and how this osmolarity is maintained.
Sharks - marine osmoconformer, but still has to regulate salt levels.
Unlike most marine fish, marine sharks and most other
chondrichthyans have tissues that are isotonic to seawater.
• Like bony fishes, sharks have an internal salt (NaCl) concentration that is lower than that of seawater salt diffuses into body Sharks need to excrete excess salt.
• Unlike bony fish, body fluids contain high concentrations of urea and TMAO.
• Salts, urea, and TMAO result in an osmolarity very close to that of seawater, and actually slightly higher than it –> water slowly diffuses into body; removed in urine.
