paper 1 required practicals Flashcards
describe the method of the microscopy required practical:
- place the slide onto the stage, use the clips to hold the slide in place.
- select the lowest power objective lens (usually 4x). position it so it almost touches the microscope slide - do this by slowly turning the coarse focussing dial, and looking at the microscope from the side.
- look down through the eyepiece, slowly turn the coarse focussing dial, moving the objective lens away from the lens until the cells come into rough focus.
- we now turn the fine focussing dial to finally bring the cells into clear focus.
- at this point, we can select a different objective lens (e.g. 10x), but we must then adjust the fine focussing dial again to bring the cells back into focus.
describe the different parts of an optical microscope:
stage: the microscope slide is placed here. it has clips to hold the slide in place.
lamp: below the stage is a lamp. light from the lamp passes up through the microscope slide, illuminating it.
(some microscopes have a mirror beneath the stage, reflecting light up through the microscope slide).
objective lenses: above the stage are a set of lenses (usually three, with magnifications of 4x, 10x, and 40x)
eyepiece: at the top of the microscope, where we look through. contains the eyepiece lens, which has a magnification of 10x.
coarse focussing dial: adjusts the distance between the objective lens and the slide.
fine focussing dial: allows the specimen to come into clear focus, when looked at through the eyepiece.
how can you calculate total magnification?
multiply the magnification of the eyepiece lens by the magnification of the objective lens.
e.g. multiplying the eyepiece lens by the low-power objective lens: 10 x 4 = 40x
what are the hazards and risks to do with the microscopy practical?
- care must be taken when handling microscope slides, as they are made of glass and can shatter. this can cause you to cut yourself with the glass.
- care must be taken when looking down the eyepiece as if the illumination is too bright, your eyes can be damaged.
describe the method for the microbiology required practical (agar gel plate, cultivating bacteria):
- a nutrient broth has been set into a jelly, using a chemical called ‘agar’. this is then poured into a petri dish and allowed to set.
- carefully sterilise all petri dishes, bacterial nutrient broth and agar, killing any unwanted microorganisms, and preventing contamination.
- bacteria is transferred into the culture using an inoculating loop (which will need to be sterilised before use, by being passed through a bunsen burner flame).
- attach the lid of the petri dish using adhesive tape, preventing the lid from falling off and unwanted microorganisms from getting in.
- place the agar plate upside down into an incubator. this method stops moisture from dripping down onto the bacteria and disturbing the colonies.
describe the growth of bacteria in a nutrient broth solution:
bacteria can grow in a nutrient broth solution, which contains all the nutrients that bacteria needs to grow and divide. the broth is often cloudy when in use, as it contains a very large number of bacteria.
how can we properly incubate the petri dish containing the bacteria colonies?
- in school labs, bacteria is usually incubated at 25 degrees celsius.
- this reduces the chance that harmful bacteria will grow.
describe the method for investigating the effect of antibiotics on bacterial growth:
- clean the bench with disinfectant solution, killing 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 any bacteria in the air.
- use the loop to spread the bacteria evenly over the plate.
- place sterile filter paper discs containing antibiotics onto the plate.
- incubate the plater at 25 degrees celsius.
- you should see a layer of bacteria on the plate, but around the antibiotic discs, you should see an area where bacteria has not grown. this is the ZONE OF INHIBITION.
what are the hazards and risks of the culturing microorganisms practicals?
- be careful around the naked flame of the bunsen burner, as a student could scald themselves on the flame.
- all equipment that has come into contact with the microorganisms should be sterilised before the next use, to avoid contamination of other objects.
describe the osmosis required practical (using a potato):
- peel the potato skin, as this could affect osmosis.
- use a cork borer to produce three cylinders of potato. this ensures all the cylinders are of the same diameter. use a scalpel to trim the cylinders to the same length (around 3cm).
- record the length of each cylinder (using a ruler) and the mass (using a balance).
- place each cylinder into a test tube. add 10cm³ of a 0.5 molar sugar solution into the first test tube. add 10cm³ of a 0.25 molar sugar solution into the second test tube, and 10cm³ of distilled water (contains no dissolved substances, which could affect the rate of osmosis) into the third test tube.
- leave the potatoes overnight, to allow osmosis to occur.
- the next day, gently roll the potato cylinders on paper towel to remove any surface moisture. (do not press on the cylinders!!)
- measure the length and mass of each cylinder again, and calculate the percentage change of length and mass.
how do you calculate the percentage change?
% change = change in value / original value
x 100
describe the food tests required practical:
PRE-TEST:
1. take food sample and distilled water, grind it with mortar and pestle. we want to make a paste.
2. transfer paste to a beaker, add more distilled water - stir so the chemicals dissolve in the water.
3. filter the solution to remove suspended food particles.
STARCH:
1. 2cm³ of food solution into the test tube.
2. add a few drops of iodine solution (originally orange).
3. if starch is present, iodine will turn blue-black. if there is no starch present, the solution will not change colour.
GLUCOSE:
1. 2cm³ of food solution into the test tube.
2. add 10 drops of Benedict’s solution (originally blue).
3. place the test tube in a beaker that’s half-filled with hot water from a kettle. leave it for around 5 minutes.
4. if sugars are present, the solution will change colour. a green colour tells us there’s a small amount of sugar, a yellow colour tells us there’s more sugar present, a brick-red colour tells us there’s lots of sugar present.
(this test only works for certain sugars, such as glucose - reducing sugars. it also isn’t fully accurate).
PROTEINS:
1. 2cm³ of food solution into the test tube, along with 2cm³ of biuret solution, which is originally blue.
2. if protein is present, the biuret solution will turn from blue to a purple/lilac colour.
LIPIDS:
1. when preparing the lipids, grind the solution with water with a mortar and pestle, but do not filter the solution, as lipid molecules can stick to the filter paper.
2. 2cm³ of food solution into the test tube, and add a few drops of distilled water, and a few drops of ethanol.
3. gently shake the solution, and if lipids are present, a white, cloudy emulsion forms.
(ethanol is highly flammable, so ensure no naked flame is present).
describe the enzymes required practical:
- place one drop of iodine (originally orange) into each well of a spotting tile.
- take three test tubes. in the first test tube, add 2cm³ of starch solution. in the second test tube, add 2cm³ of amylase solution. in the third test tube, add 2cm³ of pH 5 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 solutions into one test tube and mix with a stirring rod. return it to a water bath, and start the stopwatch.
- after 30 seconds, use a pipette to transfer one drop of the solution to a well in the spotting tile (which contains iodine).
- the iodine should turn blue-black, showing that starch is present.
- take a sample every thirty seconds and continue until the iodine remains orange (telling us that starch is no longer present in our solution and the reaction has completed).
- record the time for this in the results.
- repeat the whole experiment several times using different pH buffers, e.g. pH 6, 7 and 8.
describe the method for the rates of photosynthesis required practical:
- start by taking a boiling tube and placing it 10cm away from an LED light source (an LED light is used as it doesn’t produce as much heat, and this could change the temperature of the experiment).
- fill the boiling tube with sodium hydrogen carbonate solution - this solution releases carbon dioxide, which is needed for photosynthesis.
- place a piece of pond-weed in the boiling tube, with the cut end at the top. leave this for 5 minutes to acclimatise to the conditions in the boiling tube.
- bubbles of gas should be seen being produced from the cut end of the piece of pond-weed. this gas is oxygen, and is a product of photosynthesis.
- start a stop-watch and count the number of bubbles produced in one minute. repeat this two more times and calculate the mean number of bubbles produced in one minute.
- do this experiment all over again from the start, but this time from different distances from the light (e.g. 20, 30 centimetres).
what is a more accurate alternative to the rate of photosynthesis required practical?
instead of counting the bubbles of oxygen, which is difficult and inaccurate, measure the volume of oxygen produced.
- place the pond weed under a funnel, and catch the bubbles in a measuring cylinder filled with water.
- use the measuring cylinder to measure the volume of oxygen produced.
