Practical 2.1- The Effect of Temperature on Membranes
To investigate the effect of temperature on membrane structure Introduction
Beetroots contain Betalains which are the red pigments present in the cell vacuole. Betalains are soluble in water and they contain nitrogen. Betalains extracted from beetroot is commonly used as food dye because it is not known to cause any allergic reactions.
Picture taken from http://tipdeck/how-to-cook-beet-root
Structure of Betalain
Picture taken from http://en.wikipedia.org/wiki/File:Betanin.png
Cell membrane is the barrier that separates the inner environment of the cell from the outer environment. The membrane is selectively permeable. The cell membrane is made up of mainly lipids, carbohydrates and proteins. The lipids are the phospholipid bilayer which consists of a hydrophilic polar head and a hydrophobic tail. Among the proteins present in the cell membranes are integral proteins and peripheral proteins. Lipids increase in fluidity as temperature increases. Once denatured, proteins start to unravel and are unable to carry out their function. Diffusion is the movement of molecules from high concentration to a low concentration down a concentration gradient. Facilitated diffusion and active transport requires assistance from proteins imbedded in the cell membrane to transport substances in and out of the cell. Any damage to the cell membrane will cause the cytoplasm to leak out of the cell. Energy for the movement of molecules comes from the kinetic energy of molecules.
Structure of Cell Membrane
Picture taken from http://www.ncnr.nist.gov/programs/reflect/rp/biology/cell_membrane.html
There are two kinds of spectrophotometer which are the single beam and the double beam spectrophotometer. The single beam measures relative light intensity of a previous sample whereas the double beam compares light intensity between two light paths. In this experiment, a single beam spectrophotometer is used.
Picture taken from http://en.wikipedia.org/wiki/File:Spektrofotometri.jpg How a spectrophotometer works
Picture taken from http://en.wikipedia.org/wiki/File:Spetrophotometer-en.svg
First, light from the light source is beamed through the monochromator. The monochromator will diffract the light into several different wavelengths. An output wavelength is then selected and then beamed onto the sample in the cuvette. A fraction of the monochromatic light is transmitted to the photodetector as is passes through the sample. The output is the percentage absorbency. In a single beam spectrophotometer, it has to be calibrated by ‘zeroing’. The percentage absorbency of a reference sample is used as the base value for other substances. The reading is relative to the initial sample. Absorbency is the amount of light absorbed relative to the initial substance.
What is the effect of temperature on membranes?
An increase in temperature will cause structural damage to the membrane.
Type of variable
Ways to control
The slices of beetroot is placed in water baths of different temperatures which are 0°C, 23°C, 35°C, 45°C, 55°C and 65°C.
The light absorbance of each sample using a spectrophotometer. (% absorbency)
The surface area of the sliced beetroot sample.
Table 1.0- The manipulated, responding and constant variable and methods to control each variable
Cork borer, white tile, knife, ruler, 250 cm3 beakers, forceps, water baths at 0, room temperature, 35, 45, 55 and 65°C, boiling tubes, thermometer, spectrophotometer, cuvettes, stopwatch, , small measuring cylinder, dropping pipettes. Materials
Raw beetroot, distilled water.
1. Sections from a beetroot are cut using a cork borer. Six 2 cm length slices are cut...
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