9.4 Water Balance olute content, and ofen emperatore, Humane and many other terv

Question

9.4 Water Balance olute content, and ofen emperatore, Humane and many other tervestrial ve insidle their body and they must continuounly replenish and maiain cencertratd) ditions of the external environment change in terms of solutes and must also maintain their internal environment, molecules Adlantic selmon (Salmo nlar) spends part of ins hie cyde in both s For the first two or three years of its life, the welmon fredrwater rivers and lakes, wherea..ateconcentraton (bout 0.1 %) il concentration wihin body (about 1.0 %). This concentration gradient m ' the upeake of water into the slmonis internal environment, and therefore hoee mehanam s mat expel the exces·water from the bol. As thesalmon ma- w abandons the freshwaber environment for the salt water of the Adantic Oc the concentration of solutes is about 3.5 % In this saltwater envenme experiences a continuous los of water from its body which it must replenish. permestiol addition to changing solute concentrations, there are other important dit In addition to changing solute concentrations, there are other important die concentrated membrane ences between terrestrial and aquatic environments Because watber is not as abundan on land as it is in aquatik environments, terrestrial organisms require mechanin to conserve water and maintain a homeostatic balance of solutes within their body In this section, you will consider the following questions: Why do animals need to maintain a water balance? Why do animals need an excretory systen Osmosis In Chapter 2 you learned about the role of osmosis in the homeostatic water of cells. During osmosis, water molecules move from a region where they are highly concentrated to a region where their concentration is lower. This movement occun across a selectively permeable membrane, which allows water but very few sokte molecules to flow through. The different water concentrations on the two sides of the membrane are produced by diferent numbers of solute molecules (Figure 1(a)).The of water Figure 1 (al Two solutions have different side with a lower concentration of solutes has a higher concentration of water mol ecules. The water moves osmotically across the membrane to the other side, where the water concentration is lower (Figure 1(b)). Selective permeability is a key factor in osmosis because it helps to maintain differences in solute concentration on the tw concentrations. Osmosls occurs when water moves across a selectivel igh concentration to an area of low concentration sides of biological membranes, such as cell membranes. Proteins are among the most important solutes in establishing the conditions that produce osmosis. Osmotic pressure is the pressure that results from a difference in water concentra- tion, or a water concentration gradient, between the two sides of a selectively perme able membrane. The greater the water concentration gradient, the greater the osmotic osmotic pressure the pressure that results from a difference in solute concentration between the two sides of a selectively pemeable membrane pressure difference between the two sides. A solution with a higher concentration of solute molecules on one side of a selectively permeable membrane is said to be hyperosmotic (hypertonic) to a solution with a lower concentration of solutes on the hyperosmotle the property of the solution on one side of a selectively permeable membrane that has the lower other side. Water tends to move to the hyperosmotic side. The solution with a lower Solutions with the same solute and water concentrations are lsoosmotic (isotonic) lsoosmotic the property of two solutions but the water movement is equal in both directions so there is no net movement. solute concentration is said to be hypoosmotic (hypotonic) to the solution with the higher solute concentration. Water tends to move from the hypoosmotic solution. concentration of water hypoosmotic the property of the solution on one side of a selectively permeable membrane that has the higher concentration of water Water moves across the membrane when the two solutions have different water concentrations. This movement tends to continue until the two solutions are isoos motic. Water still moves across the membrane even when the solutions are isoosmot, that have equal water concentrations Another factor that determines whether osmosis will occur is hydrostatic, or watci, pressure. If the hydrostatic pressure on one side of a membrane (such as a plant cel membrane) is equal to the osmotic pressure on the other side of the membrane, there s no net flow of water.As water continues to cross the membrane,the internal 442 Chapter 9 Homeostasis: A Fine Balance

Explanation / Answer

Summary- Water is the most abunduant component in our body and the most important carrier of several molecules to distant organs by solubilizing them. The internal fluid of our body is stably maintained and replenished continously on depletion. Aquatic animals also switch the mode of their body-fluid homeostasis mechanism in response to the change in concentration of solutes and temperature of the external environment and thus maintain their internal environment. For example, Atlantic salmon (Salmo salar) during their infant stages live in freshwater and the solute concentration in their body being higher than the environment leads to higher influx of water into their body. Therefore, they homeostatic mechanism must efflux the excess of water into the environment, the reverse of which happens when they start to live in the salt water of the Atlantic ocean. Because in the salt water the solute concentration is very high in comparison to that in their body, the salmon must resist the continous loss of water from their body and replenish it as required.

The basic mechanism through which the regulation of body-fluid homeostasis is maintained is called osmosis. Osmotic regulation is mediated by the transport of water (solvent) from its higher concentration (lower solute concentration) to its lower concentration (higher solute concentration) across a selecively permeable membrane (for example, plasma membrane) which allows only water and few solute molecules to pass through. The solution with higher solute concentration is called hyperosmotic (hypertonic) with respect to the solution of lower solute concentration which is called hypoosmotic (hypotonic). Two solutions across the membrane are called isoosmotic (isotonic) if the solute and water concentrations of both of them are equal. So, water always moves from the hypoosmotic solution (as its concnetration is higher) and continues to flow until the two solutions become isoosmotic. During water flow, a pressure builds up resulting from the water concentration gradient which is called osmotic pressure. Water flow will remain active till the osmotic pressure of one side of the membrane is higher than the hydrostatic pressure on the other side of the membrane comes to halt when hydrostatic pressure begins to build and balances the osmotic pressure.

Water inflow occurs in plant root till the environment around it remain water rich or hypoosmotic. The interplay between osmotic pressure and hydrostatic pressure plays an important role in plant cells for generating the pressure, called turgor pressure exerted on their cell wall when water inflow causes the cell to swell and press against their cell walls. In hyperosmotic environment, water inflow falls and drop of turgor pressure occurs which results in the wilting of plant. Due to not having any cell wall, animal cells cannot build hydrostatic pressure. They shrink in hyperosmotic solution as they loose water and in hyperosmotic solution, they swell and burst when water influx continues above a threshold limit.

Related Questions

Navigate

• Browse (All)
• Browse 9
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.