Practicals

• osmosis prac

  1. Cut equal size cylinders from potato and remove any skin (non-permeable)

  2. Remove excess water from surface and weigh using top-pan balance

  3. Place each in a test tube with different concentrations of sugar solution, and leave for a set time (e.g. 1 day)

  4. Remove cylinders, dab off excess water, reweigh

  5. Calculate: Xchange in mass= (final mass-initial mass)/initial mass

  6. Plot this against concentration
• microscopy prac

  1. Peel a one-cell layer of skin from an onion using a scalpel and tweezers

  2. Place this on a microscope slide, add a drop of iodine to stain the cells, place a cover slip on top, and place on the microscope stage

  3. Turn on the light or position mirror so light reflects through the condenser to the slide

  4. Use the lowest magnification objective lens. Use the coarse and fine focus knobs to focus

  5. Increase magnification and refocus if needed

  6. Use a graticule on the slide to measure the length of cells in micrometers (μm)
• emzymes prac

  1. Measure out the enzyme and substrate (e.g. starch and amylase)

  2. Place separately in a water bath, along with buffer solution if changing the pH

  3. Prepare a spotting tile with iodine drops

  4. Mix the the reactants together and start timer

  5. Every 10 seconds, remove a drop of the mixture and put in a dimple of iodine. If it changes colour, there is still starch present

  6. Repeat this process for different temperatures, or different pH buffer solutions
• photosynthesis prac

  1. Put pond weed in test tube or measuring cylinder, add sodium hydrogen carbonate then cut stem at an angle (while submerged)

  2. Invert and put in a beaker, ensuring there is no air at the top. Carry out investigation in a dark room

  3. Position lamp/light source at a distance measured with a metre ruler. Wait 1 minute for the plant to acclimatise to the light intensity

  4. Start stopclock and count how many bubbles, or measure the volume of oxygen produced in 1 minute

  5. Change the distance and repeat