Biology A2 Practicals

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  • Topic: DNA, Oxygen, Polymerase chain reaction
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  • Published : May 3, 2013
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A2 BIOLOGY CORE PRACTICAL SUMMARY
Name of practical Independent & dependent variables
Observing patterns by Ecological sampling Random sampling Systemic sampling

Other variables to be controlled
Abiotic factors e.g. light, temperature, soil water, humidity, O2 concentration, pH, aspect, slope angle

equipment
Gridded Quadrat Tape measure Point quadrat Pitfall trap Sweep Net Pooter Tullgren funnel Baermann funnel

Method and outcome
Several methods. 1 random sampling = set up grid using tape measure, use random numbers to generate points to place quadrat to collect data. 2 systemic sampling = line transect often used especially to study zonation. A tape measure is laid along several zones to be looked at and quadrats are used to record data at regular intervals 3 Measuring abundance Density = presence of organisms per quadrat Frequency = percentage of quadrat squares containing organism Percentage cover = percentage of ground covered with organism in a quadrat (usually for plants) Pitfall trap = to collect invertebrates Sweep net = to collect invertebrates in long grasses Pooter = to collect invertebrates into a container Tullgren funnel = to collect organisms from soil or leaf litter Baermann funnel = to collect living organisms from water Decide on a range of temperatures from 5 °C to 35 °C to be tested. Place 2 g of sea salt into a 100 cm3 beaker. Add 100 cm3 of de-chlorinated water and stir until the salt completely dissolves. Label the beaker with sea salt and the temperature at which it will be incubated. Place a tiny pinch of egg cysts onto a large sheet of white paper. Wet the piece of graph paper using a few drops of salt water. Dab the paper onto the white sheet to pick up approximately 40 eggs. Use a magnifying glass to count the eggs. Put the paper with the 40 eggs into the beaker (eggs-side down). After 3 minutes, use a pair of forceps to gently remove the paper, making sure that all the egg cysts have washed off into the water. If possible replicate the treatments. Incubate the beakers at the appropriate temperatures, controlling exposure to light as far as possible. The next day count the number of hatched larvae in each of the beakers. To do this, place a bright light next to the beaker. Any larvae will swim towards the light. Using a fine glass pipette catch the brine shrimps and place them in a small beaker of salt water. Brine shrimps are very delicate and care must be taken when handling them. Record the number of larvae that have successfully hatched at each temperature. Outcome The majority of the shrimp should hatch at the optimum temperature between 25 and 30˚C. (optimum at 28˚C). Stats tests could be used to show evidence for data. Difference = student t test or mann whitney U Correlation = spearman’s rank Mix DNA with desired restriction enzyme and loading dye. Prepare agar and pour into electrophoresis mould. Once set, fill electrophoresis tank with buffer solution. Use micropipette to load restriction ladder into first well then DNA samples cut with restriction enzyme into the other wells. Connect to electrical supply, turn on and leave until the dye has moved to the opposite end of the gel tank. Switch off and disconnect electrical supply. Carefully remove the gel from the tank and view under UV light. Take picture if desired. Outcome DNA will be separated out through the agar gel, with the heaviest (biggest) DNA strands near the wells and the lightest (smallest) will be at the opposite end. The DNA restriction ladder can be used as a ‘ruler’ to measure the size of the different fragments.

Possible evaluation issues
constant changing of abiotic conditions Movement of organisms Sampling taken within a small amount of time Limitations of only 1 study Consideration for safety of organisms Disruption to normal habitat Ethics of measuring wild organisms ethics of hatching shrimp under different conditions use of animals in experiments effect of light intensity, may be a difference in...
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