Required Practicals

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Divide the plate into 3 equal sections and number them 1, 2 and 3 (on the bottom of the agar plate). • Put a dot in the middle of each section. • Add your initials, the date and name of the bacteria. 4. Wash your hands with an antibacterial handwash. 5. Put a different antiseptic onto each of the three filter paper discs, being careful to shake off excess liquid to avoid splashing. 6. Carefully lift the lid of the agar plate at an angle away from your face. Do not open it fully. 7. Use the forceps to carefully put each disc onto one of the dots that you drew earlier. 8. Make a note of which antiseptic is in each section. 9. Secure the lid of the agar plate in place using two pieces of clear tape. Do not seal the lid all the way around as this creates anaerobic conditions which will prevent the bacteria from growing and encourage other nasty bacteria. 10. Incubate the plate at 25°C for 48 hours. 11. Measure the diameter of the inhibition zone of each disc. Measure again at 90° (perpendicular) and calculate a mean. 3-Osmosis 1. Use a cork borer to cut 5 potato cylinders of the same diameter 2. Use a knife to trim off any potato skin. Then trim each potato cylinder so that they are all the same length. 3. Accurately measure the mass and length of each cylinder. Record these measurements in a table. 4. Measure 10 cm³ of each concentration of sugar/salt solution and put into labelled boiling tubes. 5. Measure 10cm³ of the distilled water to put into the fith (labelled boiling tube). 6. Add one potatoe cylinder to each boiling tube. 7. Leave the potato cylinders in the boiling tubes for a chosen amount of time. 10. Remove the potato cylinders from the boiling tube and carefully blot them dry with the paper towels. 11. Measure the new mass and length of potatoe cylinder again. Record your measurements in the table. 1 3 1.0 mol/dm³ 0.75 mol/do 0.5 mol/dm³ 0.25 mol/dm³ Distilled water 4-Food Tests Iodine Starch Browny orange- Blue black 1. Put some of the food sample into a test tube. 2. Add a few drops of iodine solution. 3. Note down any change of colour. Emulsion tests - lipids Colourless Cloudy 1. Put some of the food sample into a test tube. 2. Gently mix the sample with a few drops of ethanol. 3. Decant the dissolved liquid into another test tube containing water. 4 Observe the results. Biuret test - Proteins Blue Purple 1. Put some of food sample into a test tube 2 Add 2 cm³ of biuret solution into the test tube. 3. Shake tube gently to mix 4. Observe the result. Initial mass (g) Final mass (9) Change in mass (g) % change in mass (g) Initial length (cm) Final length (cm) Change in length (cm) % change in length (cm) / 5 Benedict's test for sugars Blue →→Green, yellow, brick 1. Set up a water bath set to 75°C. 2. Put the food sample in to a test tube 3. Add a few drops of Benedict's solution to the sample in the test tube. 4. Put the sample into the water bath for 5 minutes. 5. Notice any colour change. 5-Enzymes 1. Heat your water bath to 35°C. 2. Put 2cm ³ of each buffered solution into individual test tubes. Label each with the pH of the solution. 3. Label 5 lest tubes starch and add 4cm³ of starch solution into each tube.. 4. Put a thermometer in one of the starch test tubes to monitor the temperature. 5. Add 10cm³ of Amylase solution into another tube and label it 'amylase. 6. Put all the test tubes into a water bath and allow the solutions to reach 35°C. 7. While the solutions are reaching temperature, put one drop of iodine solution into each depression of the spotting tile. 8. Put a drop of starch solution into the first depression of the tile. This is your 'zero time` mixture. You will use this as a comparison of colour for your test buffers. 9. When all the tubes have reached 35°C, take one of the tubes of Starch from the water bath and add the 2 cm³ of first pH buffered solution. Stir the mixture with a glass rod. your 10. Use the pipette to add 2cm³ of amylase solution to the mixture. Start the stopwatch and keep stiring the mixture. 11. After 10 seconds, remove one drop of the mixture with a glass rod. Put this drop on the second depression of the spotting til 12. Rince the glass rod with water. 13. Every 10 seconds remove one drop of the mixture and put in the next depression of the spotting tile. 14. Keep sampling every 10 seconds until the iodine does not change colour. 15. Record your results in a table. 6-Photosynthesis 1. Put your 10cm piece of pondweed (cur edge at top) into a beaker of wo 2. Cover the pondweed with an inverted filter funnel - raised off of the bottom of the beaker with plasticine. 3. Fill the measuring cylinder with water and gently position it over the end of the funnel. 4. Use a ruler to position the beaker of pondweed I metre away from the light source. 5. Leave the pond weed to equilibrate for 5 minutes. 6. Start the stop watch and: • Count and record the number of bubbles released in three minutes. • Record the volume of gas produced and collected in the measuring cylinder. 7. Record your results in a table. 8. Move the light source so that the pondweed is 80cm away. 9. Refill the measuring cylinder with water and replace it. 10. Repeat steps 5, 6 and 7. 11. Repeat with distances of 60, 40 and 20 cm. 4