Biology Paper 1 Flashcards
RP1 Microscopy: How to prepare a microscope slide
- Use a dropping pipette to put a drop of water onto a glass slide
- Separate a thin layer of the tissue (eg. Onion)
- Peel off a thin layer of epidermal tissue from the inner surface
- Use a forceps to put this thin layer on to the drop of water that you have placed on the microscope slide.
- Add 2-3 drops of iodine solution onto the tissue
- Carefully lower a coverslip onto the slide using a mounted needle
- Use a piece of blotting paper to soak any excess liquid on the slide
- Put the prepared slide on the microscope stage.
RP1 Microscopy: How to use a light microscope
- Plug in and switch on the light source
- Place the slide onto the stage and use the clips to hold the slide in place
- Select the lowest power objective lens and position it so it almost touches the microscope slide ( do this by slowly turning the coarse focus dial while looking from the side)
- Look down through the eyepiece whilst slowly turing the coarse focus dial until the cells come into a rough focus
- Use the fine focus to bring the cells into a clear focus
- Calculate the total magnification by multiplying eyepiece lens and objective lens
- Repeat steps 5 and 6 using a higher objective lens
RP 2: How to prepare an uncontaminated bacterial culture using aseptic technique
- Firstly sterilise all equipment to prevent contamination.
- Sterlise the inoculating loop used to transfer bacteria using a bunsen burner flame
- Attach the lid of the petri dish using adhesive tape (to prevent any unwanted microorganisms entering)
- Next place the agar plate upside down into an incubator (to stop moisture from dripping down onto the bacteria and disrupting the colonies).
Bacteria is normally incubated at 25 degrees celsius in school laboratories. This reduces the chances that harmful bacteria will grow.
RP2: Investigate the 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 degrees celsius.
RP2: How can we use the information gathered from the experiment to compare the effects of antibiotics on bacterial growth?
Around the antibiotic discs we have a region where the bacteria have not grown. This is called the zone of inhibition. We can calculate the area of the zone ( Pi x radius squared) in order to examine the efficacy of the antibiotic.
RP 3: Osmosis
- First peel a potato (beetroot or parsnip can also be used).
- Use a cork borer to produce three cylinders of potato (which will all be the same diameter)
- Use a scalpel to trim the cylinders to the same length (around 3cm)
- 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 10cm3 of 0.5 mol sugar solution to one test tube, 0.25 mol sugar solution to another and distilled water in the last test tube
- Leave the potato cylinders overnight to allow osmosis to take place.
- Next remove the potato cylinders and gently roll them on a paper towel to remove any surface moisture.
- Measure the length and the mass of the cylinders again.
- To calculate the water gained or lost by osmosis calculate the percentage change in mass.
RP 4: Food tests - How to prepare a food solution
- Take the food sample and grind this with distilled water using a mortar and pestle.
- 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.
(Do not include step 3 for Lipids/fats as the molecules can stick to the filter paper).
RP4: Test for starch
Add (2cm3 of) starch solution into a test tube. Add a few drops of iodine solution (orange). If starch is present the solution will turn blue black.
RP4: Test for sugars (does not work for non-reducing sugars)
Add (2cm3 of) sugar solition into a test tube. Add 10 drops of benedicts (blue) solution. Leave test tube in a beaker for five minutes that is half filled with hot water from a kettle. If the solution turns brick red (a lot of) sugar is present.
RP4: Test for proteins
Add (2cm3 of) protein solution into a test tube. Add 2cm3 of biuret (blue) solution. If protein is present the solution will turn violet (or lilac).
RP4: Test for Lipids/fats
Add (2cm3 of) lipid solution into a test tube. Add a few drops of distilled water and a few drops of ethanol. Gently shake the solution. If lipids are present then a white precipitate layer (cloudy emulsion) forms.
RP 5: Effect of pH on amylase
- Place one drop of iodine solution into each well of a spotting tile.
- Take three test tubes. Add 2cm3 of starch solution to one test tube, 2cm3 of amylase solution to another and in the third test tube 2cm3 of your specific pH (eg. pH5) buffer solution.
- Place all three test tubes in a water bath at 30 degrees celsius. Leave them for 10 minutes to allow the solutions to reach the correct temperature.
- Combine the three test tubes into one test tube and mix with a stirring rod. Return the test tube to the water bath and start a stopwatch.
- After 30s use the stirring rod to transfer one drop of solution to a well in the spotting tile.
- The iodine in the spotting tile should turn blue-black indicating that starch is present
- Now take a sample every 30s and continue until the iodine remains orange (there is no colour change).
- Repeat the entire experiment (steps 1-7) using different pH buffers eg. pH 6,7 and 8.
RP 5: What does the iodine remaining orange show?
This tells us that the amylase has broken down the starch and that starch is no longer present (the reaction has completed).
RP 5: Effect of pH on amylase- problems
- We are only taking samples every 30s which means we only have an approximate time for the reaction to complete. We could address this by taking samples every 10 seconds.
- The time when the iodine does not go blue-black is not always obvious. The colour change tends to be gradual (e.g some blue-black mixed with orange). To address this ask several people to look at the spotting tile and decide when the reaction has completed.
RP 6: Photosynthesis
- Start by taking a boiling tube and placing it 10cm away from a light source.
- Fill the boiling tube with sodium hydrogen carbonate solution (releases co2 which is needed for photosynthesis)
- Put a piece of pondweed into the boiling tube with the cut end at the top
- Leave this for 5 mins to acclimatise to the conditions in the boiling tube.
- Bubbles of gas (oxygen) will be produced from the cut end of the pondweed.
- Start a stopwatch and count the number of bubbles produced in one minute.
- Repeat this twice more and calculate the mean number of bubbles produced in one minute
- Repeat the experiment from 20cm, 30cm and 40cm.
