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Biology paper 2 practicals (Investigating decay (Do this by observing the…
Biology paper 2 practicals
Investigating reaction time
Person being tested should sit with their arm resting on the table
Hold a ruler vertically between the thumb and forefinger and make sure that the 0 end is level with their thumb and finger
Let go without any warning, and see where the person catches the ruler, and repeat several times
Then the person should drink a caffeinated drink and after ten minutes repeat the experiment
You can then calculate the persons average reaction time using the readings from the ruler
Using computers
Simple computer tests to measure reaction time are more accurate than this test
They remove possibility of human error from the measurement
Using a computer also removes the possibility that the person can predict when to respond
Using quadrants
An organism might be more found more commonly in one place or than another due to differences in environmental factors between the two areas
Eg. in a playing field daisies might be more common in the open that under trees, as there is more light available
Quadrat is a square frame which encloses a known area
Place the quadrat on the ground at a random point within the first sample area eg. use a random number generator to decide coordinates
Count all the organisms within the quadrat
Repeat as many times as possible
Work out the mean number of organisms per quadrat within the first sample area
Repeat in the second area and then compare the two means so that a conclusion can be made
Using transects
Can use transect lines to find out how organisms are distributed across an area eg. if an organisms becomes more or less common as you move away from a hedge
Mark out a line in the area you want to study using a tape measure
Collect data from along the line by counting all the organisms that you're interested in that are along the line
You could also collect data by using quadrats placed along the line at even intervals
You can estimate the percentage cover of an organisms covering a particular area
Investigating decay
Do this by observing the action of the enzyme lipase on a sample of milk that has been made alkaline - when the lipase breaks the milk down, the pH of the milk decreases (fatty acids)
Phenolphthalein is used as has pink colour at pH 10 and becomes colourless at around pH 8.3
Measure out 5cm^3 of lipase and add it to a test tube which is labelled L
Measure out 5cm^3 of milk and add it to a different test tube
Steps
Add 5 drops of phenolphthalein indicator to the tube containing the milk
Then measure out 7cm^3 of sodium carbonate and add it to the tube containing the milk and the phenolphthalein - this should make the solution alkaline so it should turn pink
Add both tubes to a water bath set to 30 degrees and leave them to reach the temperature of the water bath and use a thermometer to check this
Once the tubes have reached 30 degrees use a calibrated dropping pipette to put 1cm^3 of lipase solution into the milk tube and start a stopwatch
Stir the contents of the tube with a glass rod and the enzyme will soon start to decompose the milk
As soon as the solution loses its pink colour, stop the timer and record how long the colour change took
Repeat at a range of different temperatures, and carry out the experiment at each temperature 3 times, so you can calculate the mean time taken for the colour change to occur
Rate of decay = 1000/time