Required Practicals Paper 1 Flashcards
RP 1: Microscopes
An optical microscope is used
Functions of the different parts of microscope:
Stage-This is where we place the microscope slide, the stage has clips to hold the slide in place
Lamp-light from the lamp passes up through the microscope slide
Objective lenses-most microscopes have 3 different objective lenses. These usually have a magnification of 4x, 10x or 40x
Eyepiece-where we look through, contains the eyepiece lens which has a magnification of 10x
Method:
First place the slide onto the stage and use the clips to hold the slide in place
We then select the lowest power objective lens (4x)
Position the objective lens so it almost touches the microscope slide, this is done by slowly turning the coarse focusing dial
Look down through the eyepiece and slowly turn the coarse focusing dial to increase the distance between the objective lens and the slide until the cells focus
Use the fine focusing dial to bring the cells into clear focus
Magnification= magnification of eyepiece lens X magnification of objective lens
Using a pencil make a clear labelled drawing of some of the cells
RP 2: Culturing Microorganisms
First, sterilize all Petri dishes, bacterial nutrient and agar
This kills any unwanted microorganisms and prevents contamination
Sterilize the inoculating loop by passing it through a Bunsen burner flame
Use adhesive tape to attach the lid. This stops the lid from falling off and unwanted microorganisms entering
Place the agar plate upside down into an incubator to prevent condensation droplets
Incubate at 25 degrees Celsius to reduce the chances that harmful bacteria will grow
RP 2: effect of antibiotics on bacterial growth
- Clean the bench with disinfectant solution.
This kills microorganisms that could contaminate our culture. - Sterilise an inoculating loop by passing it through a Bunsen burner flame.
- Open a sterile agar gel plate near a Bunsen burner flame. The flame kills bacteria in the air.
- Now use the loop to spread the chosen bacteria evenly over the plate.
- Place sterile filter paper discs containing antibiotic onto the plate.
- Incubate the plate at 25°C.
Calculate the area of zone of inhibition (where no bacteria are growing) by using pie r squared
RP 3: Effect of Osmosis on plant tissue
First, peel the potato as potato skin can affect osmosis
Use a cork borer to produce three cylinders of potato
Use a scalpel to trim the cylinders to the same length
Measure the length of each cylinder using a ruler and the mass of each cylinder using a balance
Place each cylinder into a test tube. Add 10cm^3 of a 0.5 molar sugar solution to the first test tube
Add 10cm^3 of 0.25 molar sugar solution to the second test tube and 10cm^3 of distilled water to the third test tube
Leave the potato cylinders overnight to allow osmosis to take place
Remove the potato cylinders and roll them on a paper towel to remove any surface moisture
Measure the length and mass of cylinders again
Calculate the percentage change in mass
RP 4: Food Tests
- Take the food sample and grind this with distilled water using a mortar and pestle. We want to make a paste.
- Transfer the paste to a beaker and add more distilled water. Stir so the chemicals in the food dissolve in the water.
- Filter the solution to remove suspended food particles.
To test for starch place food solution into a test tube
Add a few drops of iodine solution
If starch is present the iodine solution will turn from orange to blue-black
To test for sugars place food solution into a test tube
Add 10 drops of Benedict’s solution
Place test tube into a beaker half filled with hot water
If sugars are present Benedict’s solution will change from a blue color to a green/yellow/red color
To test for protein add food solution to test tube
Add biuret solution which is a blue color
If protein is present biurets solution will change to a purple/lilac color
To test for lipids add food solution to a test tube
Add a few drops of distilled water and ethanol
Gently shake solution
If lipids are present a white cloudy emulsion forms
RP 5: Effect of pH on amylase
Place one drop of iodine solution into each spot on a dimple tray
Take 3 test tubes and in one add starch solution, the next one add amylase solution, and the last one add pH 5 buffer solution
Place the test tubes in a water bath at 39 degrees Celsius. Leave for 10 minutes to allow solutions to reach the correct temperature
Combine the 3 solutions into a test tube and mix with a stirring rod. Return to the water bath and start a stop watch
After thirty seconds, use the stirring rod to transfer one drop of solution to a well in the spotting tile which contains iodine.
The iodine should turn blue-black showing starch is present
We now take a sample every thirty seconds and we continue until the iodine remains orange.
When the iodine remains orange, this tells us that starch is no longer present (the reaction has completed).
Repeat experiment using different pH buffers
RP 5: Effect of pH on amylase-problems with the experiment
We are only taking samples every thirty seconds.
This means that we only have an approximate time for the reaction to complete. We could address this by taking samples every ten seconds.
We are looking for the time when the iodine does not go blue-black. This is not always obvious.
The colour change tends to be gradual. Some wells might have a spall amountblue-blackl mixed with orange, so it can be difficult to see when the reaction has finished.
One way to address that problem is to ask several people to look at the spotting tile and decide when the reaction has completed.
RP 6: Photosynthesis
Start by placing a boiling tube 10cm away from an LED light source
Now fill the boiling tube with sodium hydrogen carbonate solution, this releases co2
Put a piece of pondweed into the boiling tube with the cut end at the top
Leave for 5 minutes
Bubbles of oxygen are produced from the cut end of the pondweed
Start a stop-watch and count the number of bubbles produced in a minute
Repeat this two more times and calculate the mean number of bubbles produced in one minute
Do the whole experiment again from the start at 20, then 30, then 40cm.
RP 6: photosynthesis- problems with the experiment
The number of bubbles can be too fast to count accurately
The bubbles are not always the same size. A large bubble would count the same as a small bubble
To solve this measure the volume of oxygen produced:
Place the pond weed under a funnel and catch the bubbles in a measuring cylinder
Use the measuring cylinder to measure the volume of oxygen gas produced
RP 6: photosynthesis-inverse square law
If we double the distance, the light intensity falls by four times
Because we need light for photosynthesis that also causes the number of oxygen bubbles to fall by four times
