What is a stage micrometre?
Specialised microscope slide with an accurate micrometre scale engraved in it.
How do you use a light microscope?
- Clip the prepared slide onto the stage.
- Select the lowest power objective lens.
- Use the course adjustment knob to raise the stage until it is almost touching the eyepiece lens.
- Look through the eyepiece lens and lower the stage until the image is roughly in focus.
- Increase the power objective lens and use the course adjustment knob until the image is roughly in focus.
- Repeat with a high power objective lens and use the fine focusing knob to make the image clear.
How do you use an eyepiece graticule and stage micrometre?
- Line up the eyepiece graticule and stage micrometre.
- Calculate the number of graticule units in one micrometre of the stage micrometre.
- Calculate the size of one graticule unit.
How do you carry out the Benedict’s test for reducing sugars?
- Add excess Benedict’s solution to a sample and heat by placing in a hot water bath that is at 100C.
- If reducing sugars are present the colour should change from blue to green, yellow, orange or brick red.
How do you carry out the Benedict’s test for non-reducing sugars?
- Add hydrochloric acid to the sample and place in hot water bath that is set to 100C.
- Take out sample and add excess sodium hydrogen carbonate to make the sample slightly alkaline.
- Add Benedict’s solution and place solution into hot water bath set at 100C.
- Take out and if sugars are present the colour should change from blue to green, yellow, orange or brick red.
How do you test for starch?
Add iodine and the colour should change from orange-brown to dark bluish black.
How do you test for Proteins?
BIURET TEST:
1. Add a few drops of sodium hydroxide to make the solution slightly alkaline.
2. Add copper (II) Sulfate solution and the colour should change from blue to purple if protein is present.
What is a colorimeter?
Device that measures the strength of a coloured solution by seeing how much light passes through it. Works by measuring the absorbance of a solution.
How do you make a calibration curve?
- Do a Benedict’s test on each solution including a negative control of pure water.
- Remove any precipitate by centrifuging the samples.
- Transfer solutions to cuvettes and use the colorimeter to make a calibration curve showing absorbance against glucose concentration.
- Test the unknown solution and use the calibration curve to find its concentration.
How can you calculate rate of reaction of a catalase enzyme?
Measure how fast oxygen is produced as hydrogen peroxide is broken down by catalase into oxygen and water
How does the Benedict’s test work?
The sugars reduce the Cu 2+ ions into Cu + ions. The copper ions then precipitate out of the solution as copper oxide.
Why do we add HCl for non-reducing sugars?
To break down the disaccharides into monosaccharides by breaking the glycosidic bond.
What part of a protein does the biuret test detect?
The peptide bonds. Copper (II) ions react with the nitrogen in the peptide bonds.
How do we test for Lipids?
We use the emulsion test.
1. Add ethanol to the sample and shake.
2. Add water to the sample and shake.
3. A white emulsion should form as lipids are non-polar so only soluble in non-polar solvents like ethanol but not water.
How does the Iodine test for starch work?
When iodine is added to a starch solution, it fits into the helical structure of amylose, resulting in a blue-black colour.
How can we measure rate of reaction of amylose?
- Fill the spotting tile with Iodine and potassium iodide.
- Add Amylose to starch solution and start stopwatch.
- After regular intervals transfer a drop of solution to the spotting tile.
- Repeat until the colour no longer changes as this means that all of the starch has been catalysed into maltose.
How can we investigate water potential?
- Prepare a serial dilution of sucrose solution.
- Use a cork borer to cut potatoes to pieces of the same size.
- Measure the mass of each potato chip.
- Place one chip in each solution and start a timer for 20 minutes.
- Remove the chips and pat dry gently with a paper towel.
- Weigh each potato again and calculate the % change in mass to plot your results onto a graph.
