Chapter 44 (1)

The general process by which animals control solute concentrations and balance water gain and loss is __. It is a process of __.

Breakdown of __ (nitrogen containing) molecules relesaes ammonia, a very toxic compound.

SEveral different mechanisms have evolved for __, the process that rids the body of nitrogenous metabolites and other waste products. Systems for __ and __ are structurally and functionally linked in many animals.

Just as __ depends on balancing heat loss and gain, regulating the chemical composition of body fulids depends on balancing teh uptake and loss of water and solutes. This process of __ is based largely on controlled movemen of solutes between internal fluids and the external environment. Because water follows solutes by osmosis, the net effect is to regulate both solute and water content.

All aniamsl face the same need for __. Over time, water uptake and loss must balance.
- excessive water uptake: swelling and bursting
- excessive water loss: shrivel

Water enters and leaves cells by __. It occurs whenever two solutions separated by the membrane differ in osmotic presssure, or __ (total solute concentration expressed as molarity or moles of solute per liter of solution.)

If two solutions separated by memrbrane have same osmoloarity, they are __. Under these onditions, water molecules cross the membrane but at equal rates in both directins. There is no net movement of water betweent hem.
When two

If two soltuions differ in osmolarity, the one with the greater concentration of solutes is said to be __,and the more dilute solution is __.
- Water flows by osmosis from a __ to a __ one.

An animal can maintain water balance in two ways. One is to be an __, which is isooosmotic with its surroundings. The second is __, which controls its internal osmolarity independent of that of its environment.

All __ are marine animals. Because an __ internal osmolarity is the same as that of its environment, there is no tendency to gain or lose water. Many __ live in water that has a stable composition and hence have a constant internal osmolarity.

__ enables animals to live in environments that are unihabitable for __, such as freshwater and terrestrial habitats. It also allows many marine animals to maintain an internal osmolarity different from that of seawater. To survive in a __ environment, an __ must instead take in water to offset osmotic loss.

Most animals, whether __ or _, cannot tolerate substantial changes in external osmolarity and are said to __. In contrast, __ animals which include certain __ and __,c an survive large fluctuations in external osmolarity.

Most marine invertebrates are __. Their osmolarity (sum of concentrations of all idssolved substances) is the same as that of seawater. They therefore face no substantial challenges in water balnace. However, because they differ considerably from seawater in the concentrations of specific solutes, they must actively transport these solutes to maintain homeostasis.

Many marine vertebrates and some marine invertebrates are __. For most of these, the ocean is a strongly dehydrating environment.
- Int he gills, specialized __ actively transport chloride ions out and sodium ions folw passively. In the kidneys, excess calcium, magnesium, and sulfate ions are excreted witht eh loss of only small amounts of wate.r

The osmoregulatory problems of freshwater animals are opposite of marine animal's. The body fluids of freshwater animals must be __ because animal cells cannot tolerate salt concentrations as low as those of lake or river water. Having internal fluids with an osmolarity higher than that of their surroundings, freshwater animals face the problems of gaining water by osmosis and losing salts by diffusion.

True or False:
Many freshwater animals, like fish, solve the problem of water balance by drinking almost no water and excreting large amts of very dilute urine. At the same time, salt s lost by diffusion and in the urine are replenished by eating. Freshwater fish also replenish salts by uptake across the gills.
True False

Extreme dehydration, or +_, is fatal for most animals. However, a few aquatic invertebrates that live in temporary ponds and in films of water around soil particles can lose almost all their body water and survive. THese animals enter dormant state when their habitants dry up, an adaptation called __.

__ requires adaptationst hat keep cell membrane sintact.

The threat of __ is a major regulatory promlem for terrestrial plants and animals.
- Adaptations that reduce water loss are key to survival on land.
o Waxy cuticle- plants; body coverings (liek waxy layers of insect exoskeletons, shells of land snails and layers of dead, keratinized skin cells covering most terrestrial vertebrates including humans) contribute to success
o many are nocturnal, which reduces evaporative water loss because of the lower temp and higher relative humidity of night air

Despite these and other adaptations, most terrestirial animals lose water through many routes: in _ and __, across their __, and from moist surfaces in __ organs. Land animal smaintain water balance by drinkign and eating moist foods nd producing water metabolically through cellular respiration.

When an animal maintains an osmolarity difference between its body and the external environment, there is an energy cost. BEcause diffusion tends to equalize concentrations in a system , __ must expend energy to maintain the osmotic gradients that cause water to move in or out. THey do so by using active transport to manipulate solute concetrations in their body fluids.

the energy cost of __ depends on how much differnent an animal's osmolarity is from its surroundings, how easily water and solutes can move across the animal's surface and how much work is required to pump solutes across the membrane.

__ accounts for 5% or more of the resting metabolic rate of many freshwater and marine bony fishes.

True or False:
The energy cost to an animal of maintaing water and salt balance is minimized by a body fluid composition adapted to the salinity of the animal's habitat. Comparing closely species reveals that the body fluids of most freshwater animals have lower solute concentrations than the body flluids of their marine relatives.
True False

What is the ultimate function of osmoregulation?
- In vertebrates and other animals with a __, the cells are bathed in an interstitial fluid that contains a mix of solutes controlled indirectly by the blood. Maintaining the composition of such fluids depends on structures ranging from cells that regulate solute movement to complex organs, like vertebrate kidney.

In most animals, osmotice regulation and metabolic waste disposal rely on one or more kinds of __- one or more layers of specialized epithelial cells that regulate solute movements. __ move specific solutes in controlled amts in specific directions. __ are typically arranged into complex tubular networks with extensive surface areas. Some __ face the outside environment directly, while others line channels connected to the outside by an opening on the body's surface.

The __ that enables the albatross to survive on seawater remained undiscovered for many years.

The adaptation that enables the albatross and other marine birds to maintain internal salt balance is a specialized nasal gland. In removing excess sodium chloride from the blood, the nasal gland relies on __.
- In the albatross' nasal gland, the net result is the secretion of fluid much saltier than the ocean. Thus,e ven though drinking seawater brings in a lot of salf, the bird achieves a net gain of water. By contrast, humans who drink a given volume of seawater must use a greater volume of water to excrete the salt load, with the result that they become dehydrated.

__ that function in maintaining water balance also often function in disposal of metabolic wastes.