Biology paper1 practicals

• Investigation into the Effect of pH on Enzyme Activity - Method

  1) Put a drop of iodine solution into every well of a spotting tile

  2) Place a Bunsen burner on a heatproof mat, & a tripod & gauze over the Bunsen burner. Put a beaker of water on top of the tripod & heat the water until it is 35°C - keep the temperature of water constant throughout the experiment

  3) Use a syringe to add 1cm³ of amylase solution and 1cm³ of a buffer solution with a pH of 5 to a boiling tube. Using test tube holders, put the tube into the beaker of water & wait for 5 minutes

  4) Next, use a different syringe to add 5cm³ of a starch solution to the boiling tube

  5) Immediately mix the contents of the boiling tube & start a stopwatch

  6) Use continuous sampling to record how long it takes for the amylase to break down all of the starch - use a dropping pipette to take a fresh sample from the boiling tube every 30 seconds & put a drop into a well. When the iodine solution stays browny-orange, starch is no longer present

  7) Repeat the experiment with the buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down
• How do you make an agar plate?

  Hot agar jelly is poured into shallow Petri dishes. When the jelly's cooled & set, inoculating loops can be used to transfer the microorganisms to the culture medium. Alternatively, a sterile dropping pipette & spreader can be used to get an even covering of bacteria. The microorganisms then multiply
• Microscopy Practical - Drawing Observations

  1) Draw what you see under the microscope using a pencil with a sharp point

  2) Make sure your drawing takes up at least half of the space available & that it is drawn with clear, unbroken lines

  3) Your drawing should not include any colouring or shading

  4) If you are drawing cells, the subcellular structures should be drawn in proportion

  5) Include a title & write down the magnification that it was observed under

  6) Label the important features of your drawing using straight, uncrossed lines
• Investigating the Effect of Antibiotics on Bacterial Growth - Method

  1) Place paper discs soaked in different types of antibiotics on an agar plate that has an even covering of bacteria. Leave some space between the discs

  2) The antibiotic should diffuse into the agar jelly. Antibiotic-resistant bacteria that aren't affected by the antibiotic will continue to grow on the agar around the paper discs, but non-resistant strains will die. A clear area will be left where the bacteria have died - an inhibition zone

  3) Make sure you use a control - a paper disc that has not been soaked in an antibiotic. Instead, soak it in sterile water so you can be sure that any difference between the growth of bacteria around the control disc & around one of the antibiotic discs is due to the effect of the antibiotic alone

  4) Leave the plate for 48 hours at 25°C

  5) The more effective the antibiotic is, the large the inhibition zone will be
• Avoiding Contamination

  1) The Petri dishes & culture medium must be sterilised before use (heating to a high temperature), to kill any unwanted microorganisms

  2) If an inoculating loop is used to transfer the bacteria to the culture medium, it should be sterilised first by passing it through a hot flame

  3) After transferring the bacteria, the lid of the Petri dish should be lightly taped on - stops any microorganisms from the air getting it

  4) The Petri dish should be stored upside down - stops drops of condensation falling onto the agar surface
• Investigating the Effect of Sugar Solutions on Plant Tissue - Method


  1) Cut up a potato into identical cylinders, and get some beakers with different sugar solutions in them: one should be pure water & another should be a very concentrated sugar solution

  2) Measure the mass of the cylinders, then leave one cylinder in each beaker for 24 hours

  3) Take them out, dry them with a paper towel & measure their masses again

  4) If the cylinders have drawn in water by osmosis, they'll have increased in mass. If water has been drawn out, they'll have decreased in mass

  5) The dependent variable is the chip mass & the independent variable is the concentration of the sugar solution. All other variables must be kept the same
• Benedict's Test - testing for sugars

  1) Prepare a food sample & transfer 5cm³ to a test tube

  2) Prepare a water bath so that it's set to 75°C

  3) Add some Benedict's solution to the test tube using a pipette

  4) Place the test tube in the water bath using a test tube holder & leave it there for 5 minutes. Ensure the tube is pointing away from you

  5) If the food sample contains a reducing sugar, the solution in the test tube will change from the normal blue colour to green, yellow or brick-red - depends how much sugar is in the food
• Iodine Solution - testing for starch

  1) Make a food sample & transfer 5cm³ of it to a test tube

  2) Add a few drops of iodine solution & gently shake the tube to mix the contents - if the sample contains starch, the colour of the solution will change from browny-orange to blue-black
• Biuret Test - testing for proteins

  1) Prepare a sample of your food & transfer 2cm³ of it to a test tube

  2) Add 2cm³ of biuret solution to the sample & mix the contents of the tube by gently shaking it

  3) If the food sample contains protein, the solution will change from blue to pink or purple
• Sudan III Test - testing for lipids

  1) Prepare a sample of the food you're testing & transfer 5cm³ into a test tube

  2) Use a pipette to add 3 drops of Sudan III stain solution to the test tube & gently shake the tube

  3) The solution stains lipids, therefore if the mixture contains lipids, it will separate out into two layers - the top layer will be bright red
• Microscopy Practical - Preparing the Slide

  1) Add a drop of water to the middle of a clean slide

  2) Cut up an onion & separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers

  3) Using the tweezers, place the epidermal tissue into the water on the slide

  4) Add a drop of iodine solution - a stain used to highlight objects in a cell by adding colour to them

  5) Place a cover slip on top - stand the cover slip upright on the slide, next to the water droplet. Then, carefully tilt & lower it so it covers the specimen. Try not to get any air bubbles under there - there'll obstruct your view
• Microscopy Practical - Using a Light Microscope

  1) Clip the slide you've prepared onto the stage

  2) Select the lowest-powered objective lens

  3) Use the coarse adjustment knob to move the stage up to just below the objective lens

  4) Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus

  5) Adjust the focus with the fine adjustment knob, until you get a clear image of what's on the slide
• Oxygen Production - Method

  Oxygen Production - Method

  1) A source of white light is placed at a specific distance from the pondweed

  2) The pondweed is left to photosynthesise for a set amount of time. As it photosynthesises, the oxygen released will collect in a capillary tube

  3) At the end of the experiment, the syringe is used to draw the gas bubble in the tube up alongside a ruler & the length of the gas bubble is measured. This is proportional to the volume of O2 produced

  4) Any variable that could affect the results should be controlled

  5) The experiment is repeated twice with the light source at the same distance & the mean volume of O2 produced is calculated

  6) Then, the whole experiment is repeated with the light source at different distances from the pondweed