RPAs Flashcards
RPA 1: Microscopy
What is the aim of this experiment?
Use a light microscope to investigate plant and animal cells.
RPA 1: Microscopy
Describe the 13-step method of this practical.
- Peel off an epidermal layer on the onion using forceps.
- Mount onto the microscope slide with a drop of water using a pipette, making sure the tissue lies flat.
- Add 2 drops of iodine solution to stain the cells.
- Place the cover slip on and make sure no air bubbles are trapped.
- Remove any excess stain by soaking it with paper towels.
- Place the slide on the stage of the microscope.
- Turn the nosepiece to select a low power objective.
- Set up the microscope by raising the stage until the cover slip touches the objective.
- Now look into the eyepiece move the stage away until the image comes into focus (doing this helps avoid you breaking the slide).
- Turn the nosepiece to select a high power objective.
- Repeat the same process as above and then look into the eyepiece and turn the fine adjustment knob until the image comes into focus.
- Make a labelled drawing of a few of the cells you can see, including any features eg. cell wall, nucleus. Write down the magnification.
- Repeat these steps using a prepared slide.
RPA 2: Microbiology
What is the aim of this experiment?
To investigate the effect of different antiseptics or antibiotics on bacterial growth on agar plates by measuring zones of inhibition.
RPA 2: Microbiology
Describe the 9-step method for this practical.
- Spray the bench you are working on with disinfectant then wipe dry with paper towels.
- On the bottom of the agar plate, mark with a permanent marker:
- 3 segments.
- A dot in the middle of each segment.
- Name of bacteria. - Wash your hands with antibacterial hand wash.
- Place the different antiseptics onto different filter paper discs.
- Lift the lid of the agar plate carefully and use forceps to place each filter paper disc onto the dots. Note down the antiseptic applied to each zone.
- Tape the lid onto the agar plate securely, but loosely enough that oxygen can still reach the bacteria.
- Place the agar plate in the incubator at 25 degrees for 48 hours.
- Measure the diameter of the clear zones after 48 hours using a ruler. Take a second measurement at 90 degrees from your first measurement and take a mean for the diameter.
(Do not remove the lid when taking measurements). - Record the results in a table.The area of the clear zones can be calculated using the formula πr2.
RPA 2: Microbiology
Describe the 2 main errors for this experiment and how they can be avoided.
- The shape of the clear zone may be irregular, so measure diameter more than once and take a mean.
- Contamination from other bacteria may happen, so always close the lid securely.
RPA 3: Osmosis
What is the aim of this experiment?
Investigate the movement of water by osmosis into or out of
the plant tissue. (Potato)
RPA 3: Osmosis
Describe a 12-step method for this practical.
- Use a cork borer to cut 5 potato cylinders.
- Trim the cylinders using a sharp knife and a ruler to 3cm.
- Measure the length and mass of each cylinder.
- Measure 10 cm^3 of the 1.0M salt/sugar solution and transfer to the first boiling tube and label.
- Repeat step 4 for other concentrations of the solution and distilled water.
- Add one potato cylinder (of known mass and length) to each boiling tube.
- Add one potato cylinder to each boiling tube.
- Leave the cylinders in the boiling tubes overnight in a test tube rack.
- Remove the cylinders from the boiling tubes and blot them dry with paper towels.
- Measure the mass of each cylinder and record your measurements in the table. Calculate the percentage changes for each cylinder.
- Plot a graph of change in mass (in g) against the concentration of sugar solution.
RPA 3: Osmosis
Describe the main error for this experiment and how it can be avoided.
- Potato discs may have different surface areas which affect the rate of osmosis, so they should be cut as evenly as possible using a ruler to measure.
RPA 3: Osmosis
Why should dry the potato cylinders after taking then out?
Because the water left on them will increase their mass.
RPA 4: Food Tests
How do you test for starch, and what does a positive result look like?
- Put some of the food sample into a test tube.
- Add a few drops of iodine solution to the food sample using a pipette.
- If starch is present, the solution turns from brown to blue-black.
RPA 4: Food Tests
How do you test for sugars, and what does a positive result look like?
- Add Benedict’s solution to the food sample in a test tube.
- Place in a hot water bath for a few minutes.
- If reducing sugar is present, a brick red precipitate is formed.
RPA 4: Food Tests
How do you test for protein, and what does a positive result look like?
- Add a few drops of Biuret’s reagent to the food sample in a test tube.
- Shake the solution to mix and wait for a few minutes.
- If protein is present, the solution turns from blue to purple.
RPA 4: Food Tests
How do you test for lipids (fats), and what does a positive result look like?
- Add a few cm^3 of ethanol to the food sample.
- Pour this mixture into a test tube of equal volumes of distilled water.
- If lipids are present, a white emulsion is formed on the surface of the mixture.
- This is called the emulsion test.
RPA 5: Enzymes
What is the aim of this experiment?
To investigate the effect of temperature/pH on the rate of activity of an amylase enzyme.
RPA 5: Enzymes
Describe an 11-step method for this practical.
- On a tile, label each well with the time (from 0 onwards) and add a drop of iodine solution to each well.
- Add 2 cm^3 of each buffer solution using a syringe (ranging from pH 3.0 to 7.0) into each labelled test tube.
- Immerse the starch solution, amylase solution, and the test tubes of buffer solution in a water bath at 25°C.
- Allow a few minutes for the temperature to become the same as the water.
- Use a syringe to add 2 cm^3 of amylase into a test tube of buffer solution.
- Use a syringe to add 2 cm^3 of starch into the same test tube and start timing immediately.
- Use the glass rod to transfer a drop of the mixture to the well labelled ‘0’ on the tile.
- Repeat step 6 every 30 seconds, rinsing the glass rod in between every test, until the iodine solution remains brown and does not turn blue-black.
- Calculate the rate of enzyme reaction by using 1/ time taken for iodine solution to remain brown.
- Repeat steps 2-8 for buffer solutions with different pH values.
- Plot a graph of the rate of enzyme reaction against pH.
