Paper 1 praticals Flashcards
(13 cards)
Steps for microscopes
Place the microscope slide (with the specimen) onto the stage. Place it down slowly to push out air bubles
* place cover slip on sample
* Use stage clips to secure the slide in place.
* Select the lowest power objective lens (usually 4x).
* Look from the side, and use the coarse focusing dial to move the objective lens down until it is just above the slide — without touching it.
* Look through the eyepiece, and slowly turn the coarse focusing dial to increase the distance between the lens and slide until the specimen comes into focus.
* Use the fine focusing dial to adjust the image and get a clearer view.
* Once focused at low power, switch to a higher power objective (e.g. 10x or 40x) if needed, and refocus using only the fine focusing dial.
Effects of Osmosis on plant tissue
- Cut equal-sized cylinders of potato using a cork borer or scalpel.
- Measure the initial mass of each potato cylinder using a balance.
- Prepare a series of sugar or salt solutions of different concentrations (e.g. 0.0 mol/dm³, 0.2, 0.4, 0.6, 0.8 mol/dm³).
- Place each potato cylinder into a different test tube or beaker containing one of the solutions.
- Leave the cylinders in the solutions for at least 30 minutes (or longer), making sure they are fully submerged.
- Remove the cylinders, gently blot them dry with paper towel to remove excess solution (so the mass measurement isn’t affected).
- Re-measure the mass of each cylinder using the same balance.
- Calculate the percentage change in mass for each potato cylinder:
culturing micro-organism
Clean the bench with disinfectant solution to kill any microorganisms that could contaminate your culture.
Sterilise the inoculating loop by passing it through a Bunsen burner flame until red hot. Allow to cool.
Open a sterile Petri dish containing nutrient agar near a Bunsen flame (to reduce airborne contamination).
Use the sterile loop to spread the chosen bacterial culture evenly over the surface of the agar.
Place sterile filter paper discs soaked in different antibiotics onto the surface of the agar using sterile forceps.
Lightly tape the lid of the Petri dish (do not seal completely) and incubate at 25°C for 48 hours.
After incubation, observe clear zones around some antibiotic discs where bacteria have not grown — these are called zones of inhibition.
Measure the diameter of each zone using a ruler.
Calculate the area of each zone using the formula:
pie x r^2
Measuring results of culturing micro-organisms
+ key words + safety
After incubation, observe clear areas (zones of inhibition) around discs.
Use a ruler to measure the diameter of the clear zone.
Larger clear zone = more effective the antibiotic/antiseptic.
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Aseptic technique – to avoid contamination.
Sterile conditions – to prevent growth of unwanted microbes.
Zone of inhibition – area where bacteria didn’t grow.
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Use 25°C max in schools to avoid culturing harmful human pathogens.
Don’t fully tape plates (risk of anaerobic bacterial growth).
Wash hands before and after.
. Test for Starch
Reagent: Iodine solution
Method: Add iodine to the food sample.
Positive result: Blue-black colour
Negative result: Brown/orange
Test for Sugars (Reducing Sugars)
Reagent: Benedict’s solution
Method:
Add Benedict’s to food sample in a test tube.
Heat in a water bath at ~75°C for 5 minutes.
Positive result: Green → Yellow → Orange → Brick red (depending on amount)
Negative result: Blue
Test for Protein
Reagent: Biuret solution
Method: Add Biuret to the sample and shake.
Positive result: Purple (mauve)
Negative result: Blue
Test for Lipids (Fats)
Reagent: Sudan III or ethanol (for ethanol test)
Method (Sudan III):
Add Sudan III to the sample
Gently shake
Positive result: Red layer forms on top
Alternative (Ethanol test):
Mix with ethanol, then add water
Cloudy/milky white layer forms = lipids present
: Effect of pH on Amylase
Add 2 cm³ of amylase solution to a test tube.
Add 2 cm³ of a buffer solution with a known pH (e.g. pH 5, 6, 7, or 8).
Add 2 cm³ of starch solution to the same test tube.
Place the test tube in a water bath set to 37°C and start a stopwatch immediately.
Every 30 seconds, use a pipette to remove a small drop of the mixture and place it onto a spotting tile that contains a drop of iodine solution.
Observe the colour change:
Blue-black = starch is still present.
Yellow/orange = starch has been broken down (reaction complete).
Record the time taken for the iodine to stop turning blue-black.
Repeat the experiment using different pH buffer solutions to see how pH affects the reaction rate.
Echanging substences
Cut agar jelly into cubes of different sizes (e.g. 1 cm³, 2 cm³, 3 cm³).
(Use agar made with sodium hydroxide and phenolphthalein — it will be pink.)
Measure the dimensions of each cube accurately with a ruler.
(You’ll need these for surface area and volume calculations.)
Pour dilute hydrochloric acid into a beaker.
(Use the same concentration for all trials — usually 0.5 M to 1 M.)
Drop one cube into the acid using forceps.
(Start your timer as soon as the cube is submerged.)
Watch the colour fade as the acid diffuses into the cube.
Stop the timer when the cube is completely colourless.
Record the time taken for that cube.
Repeat with the other cube sizes.
(Use fresh acid or rinse cubes between tests if reusing the beaker.)
Calculate surface area, volume, and SA:V ratio for each cube.
(e.g. for a 1 cm cube: SA = 6 cm², V = 1 cm³, SA:V = 6:1)
Compare the times and SA:V ratios to analyse the effect on diffusion rate.
Photosythisis
- Start by placing a boiling tube and placing it 10cm away from an LED light source
- An LED is used since they do not release much heat (Too much heat would change the temperature of the experiment)
- Now fill the boiling tube with sodium hydrogen carbonate solution
- Sodium hydrogen carbonate releases carbon di-oxide, which is needed in photosynthesis
- Put a piece of pondweed into the boiling tube with a cut end at the top
- Leave this for five minutes to acclimatize to the conditions of the boiling tube
- Should see bubbles of gas being produced from cut end of the pondweed
- This gas is oxygen and that is produced by photosynthesis
- Start a stopwatch and count number of bubbles produced in one minute
- Repeat two more times and calculate the mean number of bubbles produced in one minute
- Do the whole experiment from the start and from the start at 20cm, 30cm and 40cm.
- Main issues with the practical is the numbers of bubbles can be to fast to count accurately
- The bubbles are not always the same size. A large bubble would count the same as a small bubble (solve by measuring volume of bubbles)
- Place funnel over plant which transfers into a measuring cylinder
how to prepare a onion cell for viewing under a micrsocope
Peel a thin layer of epidermal tissue from the inside of an onion.
Place the tissue flat on a microscope slide.
Add a drop of iodine solution (stain) to the tissue.
This helps to highlight the nucleus and other parts of the cell.
Carefully place a coverslip over the tissue.
Lower it slowly using a mounted needle to avoid trapping air bubbles.
Remove any excess iodine with a piece of tissue if needed.
Place the slide on the microscope stage.
Start viewing under low power (e.g. ×4 objective lens), then increase to higher magnification (e.g. ×10 or ×40) to see the cell structures clearly.
