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Required Practicals, Microscopes, Effects of Osmosis on Plant Tissue,…
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Microscopes
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Stage - center of microscope, it is where we place the microscope slide, has clips to hold the slide in place.
Lamp - beneath stage, light passes through the slide, some microscopes have mirrors to reflect light.
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Eyepiece - top of microscope, what we look through.
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Coarse focusing knob, fine focusing knob
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3)Position the objective lens so it almost touches the microscope slide, do this by slowly turning the coarse focusing dial.
4)Look through the eye piece and slowly turn the coarse focusing dial to increase the distance between the objective lens and the slide, do this until the cells come into focus
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Effect of pH on Amylase
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2)Take 3 test tubes: in the first add 2cm^3 of starch solution, in the 2nd, add 2cm^3 of amylase solution, in the 3rd, add 2cm^3 of pH 5 buffer solution (used to control pH)
3)Leave all three test tubes in a water bath at 30.c for 10 minutes, this allows the solutions to reach the correct temperature
4)Combine all three solutions into one test tube, mix, return to the water bath and immediately start the stop watch
5)After 30 seconds, use the stirring rod to transfer one drop of solution in a well in the spotting tile.
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8)When the iodine is orange, starch is no longer present, the reaction is completed, record the time taken
9)Repeat using different pH buffers e.g. 6,7,8
10)Issues - should take every 10 seconds, more accurate time, it's not always obvious when the iodine has stayed orange
Photosynthesis
1)Place a boiling tube 10cm away from an LED light (LED is used because it doesn't generate much heat)
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2)Fill the tube with sodium hydrogen carbonate solution, which releases carbon dioxide
3)Place a piece of pondweed into tube, with a the cut end at the top
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5)Bubbles of oxygen will be being produced from the cut end, from photosynthesis
6)Start the stop watch, count the number of bubble produced in one minute
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9)Issues - hard to count bubbles, sometimes to fast, different size bubbles, solved by measuring the volume of oxygen produced by placing the pondweed under a funnel to catch the bubbles in a measuring cylinder filled with water, use the cylinder to measure the volume of oxygen produced.
Culturing Microorganisms
Avoiding contamination
Sterilise all Petri dishes, bacterial nutrient broth and agar
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Once bacteria has been transferred onto the plate, attach the lid with tape to stop the lid from falling off and unwanted microorganisms entering
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7)Measure the effectiveness of the antibiotic by measuring the radius of the inhibition zone around each disc
Food tests
Tests
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Glucose
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The Benedict's solution changes from blue to: green if there is a small amount of sugar, yellow if there is moderate sugar, brick-red for lots of sugar
Only works for certain sugars e.g. glucose (reducing sugars) doesn't work for non-reducing sugars such as sucrose
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2)Transfer the paste to a beaker and add more distilled water, stir so the chemicals in the food dissolve in the water
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