Required Practicals Paper 1 Flashcards
General tips (not a flashcard just read)
- Mention all the equipment
- State safety measures
- Remember variables
- State how you will get accurate data by reducing errors and uncertanties
Parts of the microscope and their role
- Stage + clips - where the slide goes
- Lamp - passes light through the slide
- Objective lenses - lenses with magnifications of 4x 10x and 40x
- Eyepiece - where you look through and has a lense with 10x mag
- Coarse focus
- Fine focus
How to prepare an onion cell slide
- Wash the onion and peel a one cell layer of skin using a scalpel and tweezers
- Clean slide and coverslip
- Put thin onion strip onto the slide and reposition using a toothpick
- Add a drop of iodine onto the onion - this stains the cells so they can be seen
- Slantly put the coverslip on so no air bubbles form
How to use the microscope to view a prepared slide
- Put it on the stage and attach the clips to hold it in place
- Use the lowest power objective lens
- Turn the coarse focus dial until the lens nearly touches the slide
- Look through the eyepiece and slowly turn the coarse focus dial until the cells come into focus
- Use the fine focus dial to bring the cells into a clear focus
- Repeat using different objective lenses and turn the fine focus dial
REMEMBER, INCLUDE A MAGNIFICATION SCALE IN YOUR DRAWING
How to grow bacteria in the lab
- Nutrient broth solution
- Agar gel plate with nutrients
Aspetic technique to prepare an uncontaminated bacterial culture
- Sterilise petri dishes, nutrient broth and agar
- Sterilise the inoculating loop by passing it through a bunsen flame
- Inoculate the agar with the bacteria but only open the lid slightly so less airbourne pathogens can get in
- Do this near the bunsen flame to kill airbourne pathogens as they move towards the flame
- Add 2 pieces of Cellotape to the lid to stop bacteria entering, leaving and to allow oxygen to enter
- Label, store upside down (stop condensation falling) in an incubator at 25 degrees (prevent growth of harmful human pathogens)
How to investigate the effect of an antibiotic on a bacterial growth
- Same method as before but add sterile filter paper disks with the antibiotic onto the plate
- After a few days, you should observe that around the antibiotics, there are no bacteria growing
- This is called the zone of inhibition
- The effefct of the antibiotic can be calculate using the area of the zone of inhibition
How to investigate the effects of osmosis on plant tissue
- Peel the potato to remove the skin
- Use a cork borer to produce 5 potato cylinders with the same duameter and a scalpel to trim them to the same length
- Record the mass using a mass balance
- Add each potato cylinder to a test tube and add 10cm3 of distilled water, 0.2mol sugar solution with increases of 0.2 each time
- After 24hrs, remove the potatoes and gently roll them on a paper towel to remove excess water than hadn’t been absorbed (surface moisture)
- Record the new mass
- Find the percentage change and plot a graph
How to prepare a sample of food for a food test
- USing distilled water, grind the food using a pestle + mortar to get a paste
- Transfer to a beaker, add water and stir so all the chemicals in the food dissolve in the water
- Filter the solution to remove suspended food particles
- This produces a food solution
How to test for lipids
- Add a few drops of distilled water and ethanol
- Shake gently
- If lipids are present, a cloudy white emulsion forms
How to test for carbohydrates
- Add iodine SOLUTION to the food solution
- If carbs are present, the iodine solution will turn form orange to blue-black
How to investigate the effect of pH on amylase
- Place one drop of iodine solution into each well of a spotting tile
- Set up 3 test tubes - one with 2cm3 starch soltuion, one with 2cm3 amylase solution and the last with 5cm3 pH buffer solution (to control the pH)
- Place all test tubes in a 30 degrees water bath. Leave for 10 mins to equilibrate
- Combine all solutions, mix, return to water bath and start a timer
- At 30 second intervals, transfer one drop of solution to a well until the iodine remains orange
- Repeat the whole experiment using different pH buffers (6,7 and 8)
- Plot a graph which will be a curve and the lowest point is the optimum pH
Problems with the pH amylase experiment
- 30 second samples may not be frequent enough so the time is only approximate
- The colour change tends to be gradual so it is hard to tell when the iodine isn’t blue-black
Method for photosynthesis practical
- Place LED 10cm away from boiling tube
- Fill boiling tube with water and sodium hydrogen carbonate (release carbon dioxide)
- Add pondweed with cut end at the top and leave to acclimatise
- After 5 mins, start a stopwatch and count the number of bubbles produced in one minute
- Repeat to find a mean
- Repeat at different distances e.g. 20cm, 30cm
Relationship between light intenisty and distance from light source
Inverse square law
- As distance increases, light intensity decreases
- Light intensity is proportional to the inverse of the distance from the light squared