practicals Flashcards
Investigate the effect of antiseptics or antibiotics on bacterial growth using agar plates and measuring zones of inhibition
Glass Petri dishes and
agar gel must be sterilised before use in an autoclave. Pour the sterile agar plates and allow to set fully. Sterilise
the inoculating loop, by heating it in the Bunsen burner flame.
Dip the inoculation loop into the
microorganism solution and make streaks on the surface of the agar plate. Replace the lid as soon as possible, secure with tape. Label and invert the plate, and store upside down. Incubate at a maximum temperature of 25°C in schools and colleges.
How would you clean up after Investigating the effect of antiseptics or antibiotics?
All contaminated materials need to be disposed of either in autoclave bags (for disposable materials that need to be sterilised, eg spreaders/Petri dishes) or pots (for items that are to be washed, sterilised and then reused).
It is essential that all work surfaces need to be thoroughly disinfected at the end of the activity. Ensure that hands are washed with soap and water at the end of the activity.
Investigation into the Effect of pH on Enzyme Activity method.
Set up a Bunsen burner, heatproof mat, tripod and gauze. Place a beaker of water on the gauze and adjust the flame to keep the water at about 35°C. Now put two drops of iodine solution into each spot of a spotting tile. Add 2 cm3 of amylase enzyme solution to a test tube. Place 2 cm3 of starch solution into the same tube.
Finally add 1 cm3 of pH solution to the tube. This will keep the pH constant. Mix the solution in the test tube and place it into the beaker of water on the Bunsen burner. Use a pipette to remove a few drops of solution every 20 seconds from the test tube and put them into a different well of the spotting tile. Repeat until the iodine solution stops turning black. Record the time this takes. Repeat with different pH solutions.
Food tests: test for sugars.
Benedict’s solution is used. Heat in water bath. After heating, it may go through stages - green, yellow, orange, red or brown - depending on how much glucose is present.
Food tests: tests for starch.
Peel a potato. Add iodine solution. Foods containing starch will turn a blue-black colour. The iodine test can also be used with a microscope to stain starch grains in plant cells.
Food tests: tests for proteins
Add 1 cm3 of biuret solution A to the food solution. Mix the liquids. Add 1 cm3 of biuret solution B and shake OR add 1 cm3 of biuret solution B carefully down the side of the test tube so as to form two layers. Goes purple/ purple rings between layers if present.
Food tests: test for fats.
The Sudan III test is one test used to test for lipids. Equal amounts of food are added to a test tube. Drops of Sudan III are added and shaken. If lipid is present in the sample, it stains red. Sudan III is flammable (danger)
Effect of osmosis in plant tissue.
Prepare a range of sucrose (sugar) solutions. The concentration of a solution is measured in moles per cubic decimetre written as mol dm-3. Set up a series of boiling tubes with each of these solutions. Also, set up one containing distilled water. Make sure each tube is labelled with the concentration. Peel the potato. Produce cylinders of potato using cork borer. Trim down to same length. Measure length and weigh mass. Add to test tubes. Allow for osmosis to occur. Gently dry on tissue. Measure length and mass again. Calculate % change.
Photosynthesis and light intensity practical.
Set up a boiling tube containing 45 cm3 of sodium hydrogencarbonate solution (1%). Allow the tube to stand for a few minutes and shake to disperse any air bubbles that might form. Cut a piece of the pondweed, Cabomba. The pondweed should be 8 cm long.
Use forcepts to place the pondweed in the boiling tube carefully. Make sure that you don’t damage the pondweed, or cause the liquid to overflow.
Position the boiling tube so that the pondweed is 10 cm away from the light source. Allow the boiling tube to stand for five minutes. Count the number of bubbles emerging from the cut end of the stems in one minute. Repeat the count five times and record your results. Calculate the average number of bubbles produced per minute. Repeat the experiment at different distances away from the light source.
