First Lab Report
February 20, 2013
The major objective of the experiment was to test the effect of the concentration gradient on the diffusion rate. It was hypothesized that the greater the stronger the concentration gradient, the faster the rate of diffusion would be. To test this, dialysis tubes were submerged in different concentration fructose solutions. We weighed the tubes at specific time intervals to measure the rate of diffusion of water in each different solution. The results illustrated that increased concentration gradient increases the rate of diffusion of water in the tubes. We concluded that as concentration of the solution increases, the diffusion rate of water out of the tubes increases proportionally.
The cell membrane serves many purposes, such as regulating the transport of material into and out of the cell. However, not all macromolecules enter the cell through the same way. The cell is comprised of mostly cytoplasm and floats in an aqueous, watery medium. The cell’s membrane functions as a hydrophobic phospholipid bilayer barrier between both aqueous regions. The heads of the phospholipids are hydrophilic, and thus face the aqueous regions to the inside and outside of the cell, while the hydrophobic tails face inside. Because the inner region of the cell membrane is hydrophobic, macromolecules that are also hydrophobic pass through it the most easily (Sadava 107). The cell membrane is selectively permeable, meaning that only certain substances are allowed to pass through. There are two types of transport across the membrane: passive and active transport. Passive transport does not require energy, and active transport requires outside energy, often in the form of ATP, to move substances across the membrane (Sadava 114). For this lab, the focus was on passive transport, specifically the passive process of osmosis. Osmosis is a form of diffusion. Diffusion refers to the random movement of solute particles across the cell membrane. The rate of diffusion is influenced by the temperature, molecular weight of the substance, and the concentration gradient (Farzin 33). Osmosis refers to the diffusion of water molecules across the membrane. Because water molecules are polar, they require the aid of special membrane channels called aquaporins (Sadava 118). In this lab, I tested the effect of the concentration gradient on the diffusion rate. I hypothesized that the greater the difference in concentrations, the faster the rate of diffusion. This hypothesis regarding the effect of the concentration gradient was based on previous knowledge regarding the behavior of particles within a system in pursuit of equilibrium. Water molecules naturally diffuse from an area of high concentration to an area of low concentration until equal concentrations are achieved. At this point, the rates of diffusion across the membrane are equal so as to maintain equilibrium. The theory of the effect of the concentration gradient on osmosis is rooted in the law of thermodynamics, which states that the movement of particles is ultimately influenced by the chemical potential. The chemical potential gradient that affects the flux of solutes is a product of the concentration gradient as well as other driving forces, such as the pressure gradient and temperature (Wijmans 2). The solute concentrations across a cell membrane/boundary determine the direction of the net flow of water in osmosis. If a solution is hypotonic, this means that it has a lower solute concentration than its surroundings. In order to achieve equilibrium through osmosis, water needs to leave the hypotonic cell or organism in order to dilute the surroundings, which have a much higher ratio of solute to water. Hypertonic means the exact opposite, in that the cell has a higher solute concentration than its surroundings, so water is more likely to enter...