2.4.13~ factors affecting membrane fluidity Flashcards
how can you investigate membrane permeability using beetroot
-beetroot cells contain a dark purple-red pigment
-the higher the permeability of the beetroot cell membrane, the more of this pigment leaks out of the cells
temperature method - cutting the beetroot
-use a scalpel to cut 5 equal sized cubes of beetroot–> the pieces must have the same dimensions so that they all have factors could affect the rate at which the pigment leaks out
-rinse the beetroot pieces to remove any pigment released during cutting
temperature method - adding beetroot to test tubes
-add the beetroot pieces to five different test tubes that each contain the same volume of water
temperature method - water bath
-put each test tube in a water bath at a different temperature for the same length of time (for example 10, 20, 30, 40, 50)
-this needs to be long enough to let the pigment diffuse into the water
temperature method - colourimeter
-remove the beetroot pieces, leaving just the colored water in the test tubes
-use the colourimeter to measure how much light is absorbed as it passes through each of the 5 samples of coloured liquid
-the higher the absorbance, the more pigmented must have been released, due to a greater membrane permeability
general pattern of permeability for temperature
as the temperature increases, the membrane permeability also increases
why does permeability increase with temperature - phospholipds
-phospholipds within the cell membrane move because they have more energy
-at high temperatures the phospholipid bilayer may start to melt and breakdown, further increasing permeability of the membrane
why does permeability increase with temperature - pressure
volume of water inside the cells expands, this puts pressure on the membrane, causing channel and carrier proteins to deform so they can longer control what enters and leaves the cell
why does permeability increase with temperature - conformation change
temperature effects the conformation of the proteins as at a high temperature the intermolecular forces between amino acids are broken which affects proteins specificity and function
effect of permeability in membranes when in below 0 degrees
-membrane permeability may be increased
-this can caused by channel or carrier proteins deforming at these low temperatures
-ice crystals that form can also pierce the cell membrane, making it highly permeable
limitations to method - cuvettes
-may differ in thickness, a thicker (or scratched) cuvete will absorb slightly more light
what is a cuvette
small cuboid container that holds the liquid to be measured in a colourimeter
how can cuvette differences be overcome
using the same cuvette for every reading or repeating investigation many times and finding the mean
limitations to method -beetroot size
beetroot pieces may not be identical in size and shape, meaning some test tubes could contain slightly more beetroot that others
how can differences in beetroot size be overcome
cutting the discs as accurately as possible using the scalpel and ruler, and then repeating the investigation several times to find a mean
