Paper 1 Required Practicals Flashcards
Describe how to use an optical microscope to look at cells on a microscope slide
- Place the slide onto the stage and use the clip to
hold it in place - Select the lowest power objective lens
- Slowly turn the coarse focusing knob to position the
objective lens so it almost touches the microscope
slide
look at the microscope from the slide to avoid
damaging the slide - Look down through the eyepiece and turn the coarse
focusing knob to increase the distance between the
objective lens and the slide until the cells come into
focus - Use the fine focusing dial to bring the cells into a
clear focus
Describe how to prepare an uncontaminated bacteria culture using aseptic technique
- Sterilise all petri dishes, agar and bacterial nutrient
broth to kill unwanted microorganisms and prevents
contamination - Transfer the bacteria into the solution with a sterilised
inoculating loop - Attach the lid to the petri dish with tape to stop it from
falling off - Place the agar plate upside down into an incubator
(stops moisture from dripping down and disrupting
the culture)
How can an inoculating loop be sterilised?
By running it through a flame on a bunsen burner
Why must the agar dish be placed upside down in an incubator when culturing bacteria?
To prevent moisture from dripping into the culture and unwanted microorganisms entering
Why is bacteria normally incubated at 25 degrees Celsius?
It reduced the chances that harmful bacteria will grow
Describe how to use agar plates to investigate the effects of antibiotics on bacterial growth
- Clean the bench with disinfectant
- Sterilise an inoculating loop
- Open a sterile agar plate close to a bunsen burner
flame - Use the loop to spread the chosen bacteria over the
plate - Place sterile filter paper disks containing antibiotic on
the plate - The plate is incubated at 25 degrees Celsius
Why must a sterile agar plate be opened near a bunsen flame?
To kill unwanted microorganisms in the air
Describe a method to test the effects of osmosis on plant tissue
- Use a cork borer to produce 3 cylinders of peeled
potato - Use a scalpel to trim the cylinders to the same length
- Measure the starting length and mass of each
cylinder with a ruler and balance - Put each cylinder into a test tube
- Add 10cm³ of 0.5 and 0.25mol sugar solution, and
distilled water to a different test tube each - Leave the potatoes overnight to allow osmosis to
occur - Remove the potato cylinders and roll them on a towel
to reduce surface moisture - Measure the length and mass of the cylinders
Why must the potato be peeled before the osmosis practical?
The potato skin could affect the rate of osmosis
Why must a cork borer be used to cut potatoes in the osmosis practical?
It ensures that the potatoes are all the same diameter
Why is distilled water used instead of tap water in the osmosis practical?
Distilled water contains no dissolved substances which could affect the rate of osmosis
Describe an experiment to test the effect of pH on Amylase
- Place 1 drop of iodine solution into each well of a
spotting tile - Take 3 test tubes, adding the same volume of starch,
amylase and a pH buffer solution to each - Place all 3 test tubes in a water bath at 30°C and
leave for 10 minutes to allow the solutions to reach
the same temperature - Combine the 3 solutions into one test tube and mix
with a stirring rod - Return the test tube to a water bath and start a timer
- After 30s, use the stirring rod to transfer a drop of the
solution into the well of a spotting tile
(Iodine should turn blue-black, showing that starch is
present) - Continue until the iodine remains orange and record
this time, showing that starch is no longer present in
the solution - Repeat the whole experiment using different buffers
What is the purpose of a buffer solution?
To control the pH of a solution
What are some problems with the “Effects of pH on Amylase” practical, and give solutions
- Samples are only taken every 30s, so only an
approximate can be taken
(Take samples every 10s)
- Colour change isn’t obvious as it tends to be gradual
(Ask several people to observe when reaction has
finished)
Describe an experiment to test the effect of light intensity on the rate of photosynthesis
- Take a boiling tube and place it 10cm away from an
LED light source - Fill the boiling tube with Sodium Hydrogen
Carbonate solution - Place a piece of pondweed into the boiling tube
- leave it in for 5 minutes to acclimatise to the
conditions in the boiling tube - Bubbles of gas should begin to start showing
- Start a stopwatch and count the number of bubbles
given off in a minute - Repeat this with the boiling tube 20cm away, then
30, then 40 etc
