Biology Practical Revision

Biology Practical Revision Precision Instrument Values can be recorded to the nearest … Examples Burette 0.05 cm3 25.00 cm3, 10.05 cm3 Measuring cylinder 0.5 cm3 14.0 cm3, 14.5 cm3 Electronic balance (Copy completely) 0.1 g 150.0 g, 151.8 g 0.01 g 131.00 g, 189.30 g Ruler 0.1 cm 11.0 cm, 15.8 cm Thermometer 0.5 oC 40.0 oC , 40.5 oC Stopwatch 1s 23 s, 50s Units • Density: gcm-3 • Rate: s-1 Graph answering • x à y axis Other important things 1. Describe 2 ways in which your method of using the syringe ensured the dilutions were made accurately. + WHAT DID YOU DO / HOW? • Remove the bubbles in the syringe by inverting and tapping the syringe. • Use a syringe that is only slightly larger than the volume (e.g. use a 5cm3 syringe to measure 2 cm3, 10cm3 syringe to measure 9cm3) • Do not cross-contaminate the syringe. (Dedicate one syringe to each solution) • Wash the syringe with distilled water and dry thoroughly with paper towel to prevent dilution of the solutions. 2. Why was iodine added to the onion epidermis? • To stain the onion epidermis for easy viewing under the microscope. 3. Why calculate the percentage in length? • Different cells have different initial lengths • Percentage change = can accurately reflect how much the cell contents have shrunk / increased in size. à can compare to what they were like in the beginning. 4. Why take more than 1 readings? • Calculate average • Identify anomalies

5. The comparison of the diameters would be ideal if the three slices of eggplant came from one section of the same fruit. Why? • Same starting water potential of the cell sap of the plant tissues from the same fruit. • Hence more reliable comparison can be made. 6. Why rinse the vising tubing? • Remove the starch / amylase / named solution on the exterior of the bag Variables • TLVTCM Food tests Test for starch: Iodine test 1. Add 2-3 drops of iodine onto the food substance. 2. If iodine solution turns from brown to blue-black, starch is present. If iodine remains brown, there is no starch present. Test for reducing sugar: Benedict’s test 1. Add 2cm3 of food sample into a test tube containing 2cm3 of Benedict’s solution. 2. Shake well. 3. Place the test tube into a boiling water bath for 15 minutes. 4. A positive result ranges from green to brick-red. A green precipitate shows a small amount of reducing sugar. An orange precipitate shows a moderate amount of reducing sugar. A brick-red precipitate shows a large amount of reducing sugar. Test for protein: Biuret test 1. Add 2cm3 of sodium hydroxide to 2cm3 of food sample. Shake well. 2. Add 1% copper (ll) sulfate solution, shaking after each drop. 3. A violet colouration shows the presence of protein. A blue solution shows the absence of protein. Test for fats: Ethanol emulsion test 1. Add 2cm3 of ethanol to a test tube containing a mixture. Shake well. 2. Add 2cm3 of water to the mixture. Shake well. 3. The presence of a white emulsion shows the presence of fats. T