Membrane Behaviour Lab

5 May 2016

The permeability of a cell to solutes in an aqueous medium depends upon the physical and chemical make–up of the membrane. The maintenance of the living cell depends upon the continued presence and functioning of a selectively permeable membrane.

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If the nature of the membrane is changed or altered in any way, this may well affect its permeability and thus the properties of the cell of which it is a part. Irreversible changes in the permeability of the membrane usually lead to the death of the cell. In this experiment, you will study the effect of changes in environmental conditions on the permeability of living beetroot cells.

1.Top and bottom of beetroot were cut off by scalpel. The cork borer was used to cut out about 3-4 cores, then each core was cut into uniform discs about 2mm thick. 2.Discs were rinsed in a small beaker of cool water for about 5 minutes. 3.Each stock solution of HCl, NaCl and tap water were measured in a graduated cylinder to 10ml, then poured into individually labeled test tubes. 4.Three beetroot discs were placed in each test tube with tweezers. 5.After 40 minute of waiting the colour and intensity was recorded.

The Effect of Freezing

1.10 ml of room temperature water was measured with a graduated cylinder and poured into a labeled test tube. 2.Three frozen discs of beetroot were placed into the test tube of room temperature water. 3.After 40 minutes of waiting the colour and intensity was recorded.

The Effect of Organic Solvents

1.10 ml of acetone was measured with a graduated cylinder and poured into a labeled test tube. 2. Three beetroot discs were placed into the test tube of acetone. 3.After 40 minutes of waiting the colour and intensity was recorded.

a) There appears to be a marked change in the permeability of the membrane as low as the 30oc mark. b) Not all optimal temperatures for the functioning of the cell membrane are the same for different organisms and differing cell types. Cell membranes adjust their structure accordingly to their surrounding environment and in turn the function they perform is specialized for that particular environment.

However, if the conditions in which the membrane and its components best function become too extreme, the structure is found to undergo gross structural changes. When this occurs, the membrane cannot perform its necessary functions. In conclusion, differing cells and their membranes function in varying optimal conditions. c) Embedded in the cell membrane are various proteins serving different functions, however, one common purpose they do serve is to hold the membrane together in an identifiable, regular structure. Along with this, these proteins limit the passage of molecules in and out of the cell.

If the membrane is exposed to extreme conditions such as heat, these proteins may become denatured, chemical bonds become broken and ultimately, they lose the ability to perform their function. This results in the cell membrane becoming more fluid as well, increasing movement and allowing the entry of unwanted molecules into the cell and vital particles escape the cell. When this occurs, important functions and chemical reactions of the cell are interrupted and the cell ultimately dies.

2) pH

a)The chemistry terms pH and concentration are connected in several ways. The pH scale measures hydrogen ions in a solution. The concentration of hydrogen ions determines whether a solution will behave as an acid, base, or both (neutral). The properties of acids and bases are determined by pH and the concentration of the acid and base molecules in a solution.

Together, the pH and concentration determine predictable changes to the properties of any given acid or base solution. Another connection between pH and concentration is that both are calculated in a similar way. The simplest connection between pH and concentration also exists because of the scale used. They become linearly connected by a factor of ten and the pH changes by a factor of one when hydrogen ion concentration changes by a factor of ten.

b)At a pH 1 of HCl shows to be where maximum intensity of anthocyanin occur, being a very strong red. At a pH 13 of NaOH shows also to be where maximum intensity of anthocyanin occur, being a yellowish/ green colour. The pH of 7 and therefore tap water (being neutral) shows to be where minimum intensity of anthocyanin occurs.

c)pH affects membranes by affecting the proteins that make up about 70% of most cell membranes (less in inactive cells, such as red blood cells, more in others, such as those of mitochondria). Proteins are made of amino- acids and each amino-acid has a variable number of nitrogen and oxygen atoms in it. These can form hydogen bonds with the many hydrogen atoms found in the molecule.

The protein folds up to ensure that the maximum number of these hydrogen bonds is made. When the pH of a solution changes, the position of some of these hydrogen atoms also changes. This is because amino-acids are amphomeric, and tend to stabilize pH. Thus, they can lose an H+ ion at the COOH [or ‘acid’] part of the molecule at higher pHs, or gain an H+ ion at the NH2 [or ‘amino’] end of the molecule at lower pHs.

This, in turn, causes the overall shape of the protein to change with pH. This is the reason why most enzymes (which need a precisely-shaped ‘active site’) can only work well at a certain pH. Unlike heat, the denaturing of a protein by changing pH is (normally) reversible.

The dye in beetroot diffuses out of the cell when the membrane proteins are damged.

d)Anthocyanins can be used as a pH indicator. Most indicators detect the gain or loss of a hydrogen proton –H+ by the pigment. Anthocyanins are a little different from most acid/base indicators in that the color changes come about via the gain or loss of an OH- (hydroxyl ion) and is shown by the anthocyanin turning a dark red at a pH of 1 or tuning a yellowish/green at a pH of 13. A

nthocyanin can also be a natural food color solution to be a colour such as orange, red, pink and purple to blue. However, anthocyanin is most commonly used for coloring of beverages, fruit preparations, confectionery and ice cream. e)A basic solution with a pH of 13 makes the anthocyanin colour turn a yellowish/green. If an acidic solution such as 0.1M HCl is added drop by drop to the basic solution it will slowly create a neutralization reaction between the basic and acidic solution creating water and salt. A neutral solution should have a close pH of 7 therefore the colour of anthocyanin will become a light pink. 3) Freezing

a)Cells ordinarily can survive freezing in a state of suspension if done appropriately and quickly; this is done to store living samples such as sperm, cell cultures, and so on. Cold- hardened plant species can also
acclimate to cooler temperatures. However, with slow cooling and freezing, the cell membrane loses its fluidity and its semi-permeable nature.

Since water’s solid phase is less dense than its liquid state, the process of freezing expands the water, but the cell membrane, which is stiffer at these temperatures, cannot expand to accommodate the solid ice. Ice crystals form and rupture the cell membrane (and other organelles). One paper by Stout, Majak and Reaney (1980) also notes that phosphatidylcholine is broken down at sub-zero temperatures like those of a freezer; an important component of the phospholipids making up the bilayer is also damaged. b)

4) Organic Solvents
a) The presence of an organic solvent effects the permeability of the cell membrane to be very weak causing the solution to be a very deep red Permeability of a cell to solutes in an aqueous medium depends upon the physical and chemical make-up of the membrane.

The maintenance of the living cell depends upon the continued presence and functioning of a selectively permeable membrane. If the membrane is altered in any way, this may have an effect on its permeability and therefore the properties of the cell of which it is a part. Irreversible changes in the permeability of the membrane usually lead to the death of the cell.

The cell membrane provides a boundary between the cell’s inner environment and its surrounding outer environment. It allows different substances to pass through at varying rates, this is described are differentially permeable. It controls things such as sugar concentration, ion concentration and pH levels. If the pH levels were to be affected, the enzymes would not function efficiently thus allowing chemical reactions to take place. b) Organic solvents will disrupt the phosphlipid bilayer of the membrane by dissolving the hydrophobic fatty acids.

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