The theoretical background for this exercise is to be reviewed in your text book. The intracellular fluid of erythrocytes is a solution of salts, glucose, protein and hemoglobin. When subjected to hypertonic media e.
On the other hand, in a hypotonic environment e. The phenomenon of slow cooling cryoinjury has remained one of the primary areas of research in cryobiology since the early s when it was first investigated thoroughly. Lovelock demonstrated that cell death from freezing and thawing was mainly due to exposure to hypertonic solutions and the subsequent dilution back to isotonic conditions.
He suggested that the cell became permeable to sodium in hypertonic conditions leading to a loading of sodium during the hypertonic exposure, which caused the cell to swell past its elastic limit during resuspension in isotonic media post-hypertonic lysis. This idea was pursued by Zade-Oppen, Farrant, and others who were able to show that the membrane became leaky to cations in hypertonic media but they could not provide any mechanism that would cause the cell to load up with sodium other than an exchange of extracellular sodium for intracellular potassium, leaving the cell with the same cation concentration that it started out with.
On the other extreme, a red blood cell that is hypotonic lower concentration outside the cell will result in more water flowing into the cell than out.
This results in swelling of the cell and potential hemolysis bursting of the cell. In an isotonic solution, the flow of water in and out of the cell is happening at the same rate.
Osmosis is the diffusion of water molecules across a semipermeable membrane from an area of lower concentration solution i. Water moves into and out of cells by osmosis. A red blood cell will swell and undergo hemolysis burst when placed in a hypotonic solution. When placed in a hypertonic solution, a red blood cell will lose water and undergo crenation shrivel.
Animal cells tend to do best in an isotonic environment, where the flow of water in and out of the cell is occurring at equal rates. Passive transport is a way that small molecules or ions move across the cell membrane without input of energy by the cell. The three main kinds of passive transport are diffusion or simple diffusion , osmosis, and facilitated diffusion.
Simple diffusion and osmosis do not involve transport proteins. Facilitated diffusion requires the assistance of proteins. Diffusion is the movement of molecules from an area of high concentration of the molecules to an area with a lower concentration.
For cell transport, diffusion is the movement of small molecules across the cell membrane. The difference in the concentrations of the molecules in the two areas is called the concentration gradient. The kinetic energy of the molecules results in random motion, causing diffusion. In simple diffusion, this process proceeds without the aid of a transport protein. It is the random motion of the molecules that causes them to move from an area of high concentration to an area with a lower concentration.
Diffusion will continue until the concentration gradient has been eliminated. Since diffusion moves materials from an area of higher concentration to the lower, it is described as moving solutes "down the concentration gradient". The end result is an equal concentration, or equilibrium , of molecules on both sides of the membrane. At equilibrium, movement of molecules does not stop.
At equilibrium, there is equal movement of materials in both directions. Not everything can make it into your cells. Your cells have a plasma membrane that helps to guard your cells from unwanted intruders. If the outside environment of a cell is water-based, and the inside of the cell is also mostly water, something has to make sure the cell stays intact in this environment. What would happen if a cell dissolved in water, like sugar does?
Obviously, the cell could not survive in such an environment. So something must protect the cell and allow it to survive in its water-based environment. All cells have a barrier around them that separates them from the environment and from other cells.
This barrier is called the plasma membrane , or cell membrane.
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