PRACTICALS Flashcards
1.1- Meselson and Stahl test results
AFTER ONE GENERATION- The middle line can be explained by allof the DNA hving half light and half heavy nitrogen
AFTER TWO GENERATIONS- One line in the middle and one above, half the DNA has both strands light and half of the DNA has half heavy half light
1.1- How to test for reducing sugars
BENEDICTS TEST
Add benedicts to solution and heat in a water bath, solution will change from blue-green-yellow-orange to form a brick red precipitate. A non-reducing sugar can be identified through hydrolysing the solution first with dilute HCl,heat up in a water bath and then neutralised with NaHCO3, then carry out the practical as before and it should give a positive result.
1.1- How to test for protein
BIRUET TEST
-Add equal volumes of KOH solution to a test sample,followed by a few drops of dilute CuSO4 and shaking gently
-If no protein is present, the solution will stay blue, but a positive result will give a lilac colour
1.2 Simple dilutions
Concentration of solution = volume of solution as equal + excess water to bring volume to 100
1.2 Enzyme immobolisation practical
-Milk initially has no effect on a clinistix strip but after passing through a cloumn of alginate beads with immobilised lactase the clinistix test becomes positive
-This can be explained by the lactose being broken down into glucose and galactose, and it is the glucose that gives the positive test result
1.2 Serial dilutions
In one test tube, 10cm3 of starch solution
-Next test tube add 1cm3 of starch and 9cm3 of water
-Continue, consecutive test tubes will have 1/10, 1/100 etc
1.3 Using a colorimeter
-Always choose a filter the opposite end of the spectrum to the colour change observed to maximise % transmission change
-A ‘blank’ is used containing water and a drop of food colouring to set the transmission to 100% to calibrate and should be done inbetween each reading
1.3 Improving accuracy and validity of the colorimeter
-Rinse and dry the cuvette between samples
-Ensure that the cuvettes are filled to the correct level
-Ensure that the orientation of the cuvette in the colorimeter is correct
-Re-calibrate between each sample
1.3 Actual size=
Size in image / magnification
CHECK YR13 NOTES FOR CALIBRATION
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1.4 Measuring the average water potential of cells in a plant tissue
-Add water and a series of sucrose solutions of different concentrations each to separate beakers
-Use a cork borer to cut sections of potato, and use the same borer for each sample so they are all the same width and cut them all to the same size
-Potatoes should be surface dried and reweiged
-One otato cylinder should be added to each of the solutions
-After a set period of time, the potatoes are removed, surface dried and reweighed
1.4 Using a colorimter to investigate the effect of temperature on the permeability of cell surface membranes in beetroot
-Cut several small sections of beetroot of equal size using a cork borer
-Rinse the beetroot in a beaker of water and repeat until the water runs clear
-Set up a number of water baths in 10’ increments
-Take 5 test tubes and add 10cm3 of water to each. Place one in each of the water baths for 5 minutes to allow the temperature of the water to fully equilibriate
-Blot the beetroot dry and place one in each test tube and leave for 10 minutes
-Set up a colorimeter with a blue filter, distilled water ould be used as calibration
-Sample the water surrounding the beetroots and check its % transmission for each temperature
