Osmosis

7 Key excerpts on "Osmosis"

• 

  eBook - ePub

  Cambridge O Level Biology 5090

  • Azhar ul Haque Sario, Azhar ul Haque Sario(Authors)
  • 2023(Publication Date)
  • tredition

    (Publisher)

  Factors Influencing Diffusion: Apart from kinetic energy, several factors affect the rate of diffusion. These include the concentration gradient (the difference in concentration between two areas), the temperature, the size of the particles, and the nature of the medium through which diffusion occurs.

  Understanding Osmosis

  Defining Osmosis: Osmosis is a special type of diffusion. It specifically refers to the movement of water molecules across a semi-permeable membrane from an area of lower solute concentration (more water) to an area of higher solute concentration (less water).

  Kinetic Energy in Osmosis: Just like in diffusion, the kinetic energy of water molecules is the driving force behind Osmosis. Water molecules move randomly and, when they encounter a semi-permeable membrane, those that can pass through do so, moving toward the area with a higher solute concentration.

  Equilibrium in Osmosis: Osmosis continues until the concentration of the solute is equal on both sides of the membrane, or until the osmotic pressure (the pressure required to prevent the flow of water across the membrane) balances the movement of water.

  The Impact and Importance of These Processes Biological Significance: In biological systems, diffusion and Osmosis are crucial for the transport of substances within and between cells. They play a vital role in nutrient absorption, waste removal, and maintaining the balance of fluids and electrolytes.

  Cellular Functionality: Cells rely on diffusion and Osmosis to transport materials like oxygen, carbon dioxide, and other small molecules. The selective permeability of cell membranes, coupled with these processes, ensures that cells function optimally.

  Homeostasis: Diffusion and Osmosis are integral to maintaining homeostasis – the stable internal conditions necessary for survival. For example, osmoregulation, the control of water balance, is a key aspect of homeostasis in many organisms.

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  eBook - ePub

  Netter's Essential Physiology E-Book

  Netter's Essential Physiology E-Book

  • Susan Mulroney, Adam Myers(Authors)
  • 2015(Publication Date)
  • Elsevier

    (Publisher)

  The movement of water across the membrane by diffusion is termed Osmosis, and the permeability of the membrane determines whether diffusion of solute or Osmosis (water movement) occurs. The concentration of the impermeable solute will determine how much water will move through the membrane to achieve osmolar equilibration between ECF and ICF. Whereas osmolarity of a solution describes the concentration of dissolved particles and a solution can be described as hypo-osmotic, isosmotic, or hyperosmotic relative to another solution, whether fluid shifts will occur between two isosmotic solutions across a membrane depends on whether the solutes are permeant. The monosaccharide sucrose is impermeant to cells, and if infused into the plasma (ECF), it will stay in the ECF compartment. Thus a 300 mOsm/L solution of sucrose is isotonic relative to cells with normal osmolarity of 300 mOsm/L, and no fluid shift occurs. A sucrose solution of more than 300 mOsm/L is hypertonic, and a sucrose solution of less than 300 mOsm/L is hypotonic relative to normal cellular osmolarity. In contrast to impermeant solutes, a permeant solute, such as urea, will diffuse freely into cells until it reaches equilibrium. Thus a 300 mOsm/L solution of urea will be hypotonic even though the solution is isosmotic. When this solution is infused into the ECF, it will cause expansion of the ICF compartment. Osmosis occurs when osmotic pressure is present. Osmotic pressure is equivalent to the hydrostatic pressure necessary to prevent movement of fluid through a semipermeable membrane by Osmosis. The idea can be illustrated by using a U-shaped tube with different concentrations of solute on either side of an ideal semipermeable membrane (i.e., the membrane is permeable to water but is impermeable to solute; Fig

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  eBook - ePub

  Introductory Bioelectronics

  For Engineers and Physical Scientists

  • Ronald R. Pethig, Stewart Smith(Authors)
  • 2012(Publication Date)
  • Wiley

    (Publisher)

  K is determined from the relative solubilities in water and oil at equilibrium by the equation:

  The diffusion of water through the plasma membrane is of such importance to the cell that it is given a special name: Osmosis .

  3.5.2 Osmosis

  Osmosis is a special term used for the diffusion of water through cell membranes. Although water is a polar molecule, it is able to pass through the lipid bilayer of the plasma membrane. Selective transport of water molecules, in single file, also takes place through pores formed by transmembrane proteins called aquaporins (Peter Agre received the 2003 Nobel Prize in Chemistry for their discovery).

  Water passes by diffusion from a region of higher to a region of lower water concentration. Osmosis through a selectively permeable membrane is illustrated in Figure 3.11 . Water is never transported actively – it never moves against its concentration gradient. However, the concentration of water can be altered by the active transport of solutes, and thus its movement in and out of the cell can be controlled.

  Figure 3.11 Osmosis is the term given to the diffusion of water from a region of high concentration (high potential) of water molecules to a region of low concentration (low potential) across a partially permeable membrane. Water is shown here passing from a dilute to a high concentration of impermeable sugar molecules.

  3.5.2.1 Hypotonic Solutions

  If the concentration of water in the medium surrounding a cell is greater than that of the cytosol, the medium is said to be hypotonic. Water enters the cell by Osmosis. A simplified depiction of this osmotic process is shown in Figure 3.12 . As shown in Figure 3.10 a red blood cell placed in a hypotonic solution (e.g. 0.1% salt solution) will burst (haemolysis) as a result of the influx of water. White blood cells with their nucleus and more extensive cytoskeleton will expand but are less likely to burst. Bacteria and plant cells avoid bursting in hypotonic solutions because of strong cell walls. These allow the buildup of turgor

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  eBook - ePub

  Osmotic and Ionic Regulation

  Cells and Animals

  • David H. Evans(Author)
  • 2008(Publication Date)
  • CRC Press

    (Publisher)

  22

  II. WATER PERMEATION

  An understanding of the movement of water across cell membranes is essential to an understanding of the physical basis for osmoregulation. The volume of fluid compartments (intracellular or extracellular) is for, practical purposes, equal to the volume of water that resides therein, and the (passive) distribution of water is determined entirely by the distribution of solutes.

  A.  DRIVING FORCES FOR WATER MOVEMENT

  In one sense, water movements are incredibly simple; water permeation is a passive process. There is no evidence for active water transport; water movement is driven entirely by the gradient of the chemical potential of water. For biological membranes separating two aqueous solutions (for which standard chemical potential of water will be the same), the transmembrane difference in the chemical potential of water given by Equation 1.14 is:

  Δ μ w     =   ν w   ( Δ P −   R T   Δ C s )

  (1.15)

  which we can express in the practical units of pressure by dividing by the partial molar volume of water (vw ) to yield:

  Δ μ w ν w     =   Δ P −   R T   Δ C s

  (1.16)

  The driving force for passive water transport, as it is often described, is the difference between the hydrostatic pressure gradient (ΔΡ) and the gradient of “osmotic pressure” (Δπ) where Δπ = RTΔCs . This conventional usage can be confusing because π is not a pressure; rather, π is a so-called colligative property of the solution, a measure of composition. Likewise, Δπ is not a pressure difference; it is an expression of the difference in water concentration across the membrane. The association of Δπ with a pressure arises from an analysis of the equilibrium distribution of water across a membrane that is permeable to water but impermeable to solute and is configured such that a hydrostatic pressure can be applied to one side as indicated in Figure 1.3 . If a single, impermeant solute (s) is present on both sides of the membrane such that Cs (2) > Cs (1), then the resulting concentration gradient of water will drive water from side 1 to side 2—that is, from high water concentration to low water concentration. An equilibrium can be established by applying a pressure to the piston on side 2 such that the water flow, denoted here as the volume flow Jv (see below) is reduced to zero. In this condition, Δμ

  w

  equals zero, and from Equation 1.16 we obtain the classic van’t Hoff equation22

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  eBook - ePub

  Anatomy & Physiology For Dummies

  • Erin Odya, Maggie A. Norris(Authors)
  • 2017(Publication Date)
  • For Dummies

    (Publisher)

  Chapter 16 .) Cellular and extracellular fluids are constantly being “stirred” and are at temperatures between 95 and 100 degrees Fahrenheit. Molecules to which the cell membrane is permeable (such as oxygen and carbon dioxide) may diffuse into or out of the cell, constantly attempting to reach equilibrium.

  The cell membrane is generally not permeable to ions and larger molecules like glucose. They must enter (or leave) the cell through a transport protein via facilitated diffusion. This still doesn’t require energy because the molecules are moving down their concentration gradient — they just need a door to open for them.
• Osmosis: The diffusion of water molecules across a selectively permeable membrane gets a special name: Osmosis. As with diffusion, a concentration gradient drives the mechanism. The pressure at which the movement of water across a membrane stops (that is, when the concentration of the solutions on either side of the membrane is equal) is termed the osmotic pressure of the system.
• Filtration: This form of passive transport occurs during capillary exchange. (Capillaries are the smallest blood vessels — they bridge arterioles and venules; see Chapter 9 ). Capillaries are only one cell layer thick, and the capillary wall acts as a filter, controlling the entrance and exit of small molecules. Small molecules dissolved in tissue fluid, such as carbon dioxide and water, are pushed through the capillary wall, sliding between the cells and into the blood, while substances dissolved in the blood, such as glucose and oxygen, do the same in the opposite direction. The pulsating force of blood flow provides a steady force to drive this movement.
  The blood pressure in the capillaries is highest at the arterial end and lowest at the venous end. At the arterial end, blood pressure pushes substances through the capillary wall and into the tissue fluid. At the venous end, lower blood pressure (thus higher net osmotic pressure) pulls water from the extracellular fluid (and anything dissolved in it) into the capillary.