GCSE EDEXCEL BIOLOGY CORE PRACTICLES Questions And 100% Verified Guaranteed Answers Graded A+.

CP01: LOOKING AT CELLS - correct answer --- Describe how you would prepare a microscope slide for analysis - correct answer - Peel off epidermal layer using forceps - Place sample on drop of water on microscope slide - Add drops of iodine solution to sample - Lower cover slip onto sample using mounting needle Why is a thin sample of tissue required? - correct answer Allows light to pass through so internal structures can be observed Why is water added to the slide before the sample is mounted? - correct answer Allows the sample to be suspended between the slide and the cover slip, and ensures the cover slip stays in place Why is iodine solution added to stain the cells? - correct answer Iodine solution adds contrast - reacts with starch in plant cells and turns blue-black; allows internal structures (e.g. nucleus) to become more visible Why is the cover slip lowered using a mounting needle? - correct answer Ensures that no air bubbles are trapped How would you measure the length of a cell viewed under the microscope? - correct answer Measure using eyepiece graticule and calibrate with stage micrometer How would you calculate the magnification of an image? - correct answer Magnification = observed cell length / actual cell length What safety precautions should be taken during this experiment? - correct answer Wear safety goggles when handling iodine solution CPO2: PH AND ENZYME ACTIVITY - correct answer --- How is pH controlled? - correct answer By adding buffer solutions with different pH values How is the rate of enzyme activity measured? - correct answer By testing the enzyme-substrate solution for the presence of starch at fixed intervals, to find the time taken for all the starch to be digested. Rate = 1/time How is the presence of starch tested? - correct answer Using iodine solution. If starch is present, the solution turns from brown to blue-black. How can the reliability of the results be improved? - correct answer By repeating the practical at each pH at least 3 times and take a mean of the time taken to find the rate. How can the accuracy of the estimate of the optimum pH be improved? - correct answer By repeating the practical at smaller pH intervals around the estimated optimum pH State a source of error in this practical - correct answer The time intervals between testing may be too long to accurately find the time taken for all the starch to be broken down. State a hazard and safety precaution in this practical - correct answer Iodine solution is an irritant. Avoid contact with skin and eyes CP03: FOOD TESTS - correct answer --- Describe how you would prepare a sample of food to be tested - correct answer Grind up food samples using pestle and mortar Mix with water Filter with funnel and filter paper Describe how you would test for the presence of starch in a sample - correct answer Add iodine solution to sample If starch is present, solution turns from brown to blue-black Describe how you would test for the presence of a reducing sugar in a sample - correct answer Add Benedict's reagent to sample Boil test tube in a hot water bath If reducing sugar is present, a brick red precipitate forms. If not, the solution remains blue Describe how you would test for the presence of protein in a sample - correct answer Add Biuret reagent (potassium hydroxide and copper (II) sulphate) Shake mixture If protein is present, solution turns from blue to purple Describe how you would test for the presence of lipids in a sample - correct answer Add ethanol to the sample Add water to sample Shake test tube White emulsion formed if lipid present CP04: OSMOSIS - correct answer --- What is osmosis? - correct answer The movement of water molecules from a higher water potential to a lower water potential through a partially permeable membrane Describe how you would carry out an investigation into osmosis using potato tissue - correct answer - Cut identical potato cylinders using a cork borer - Measure and record the length and mass of cylinders using ruler and balance - Add each cylinder to one of three solutions: 1M sugar solution, 0.5M sugar solution and distilled water - Leave cylinders in tubes overnight - Remove cylinders from tubes and blot them using paper towels - Record length and mass of each cylinder - Draw graph of change in mass in grams (y axis) against concentration of solution in mol dm-3 (x axis Why is it necessary to use a cork borer to cut the cylinders? - correct answer Results in equal sized samples so changes in length and mass can be compared easily Why is it necessary to blot the cylinders with paper after removing them? - correct answer Each cylinder may have a different amount of water on its surface, so masses may vary. Blotting cylinders allows masses to be comparable What safety precautions should be taken with this experiment? - correct answer Handle cork borer and scalpel with care How can the water potential of the plant cells be found? - correct answer Plot a graph of change in mass against concentration. Find the x-intercept, which is the concentration of solution that is isotonic to the plant cells. State a source of error in this practical. - correct answer Plant tissue taken from different parts of the plant may have different water potentials CP05: MICROBIAL CULTURES - correct answer --- What antiseptic techniques can be used to avoid contamination? - correct answer - Spray working area with disinfectant and wipe dry - Wash hands with antibacterial wash - Flame the neck of the culture bottle - Lift the lid of the agar plate at an angle - Dip spreader in ethanol and pass through Bunsen flame before spreading bacteria - Use forceps to place antibiotic discs Describe how you could investigate the effect of antibiotics on bacterial growth using zones of inhibition - correct answer - Divide agar plate with bacteria into three segments - Use forceps to place filter paper disc with antiseptic in each zone - Loosely tape lid onto agar plate to allow oxygen to reach bacteria - Incubate at 25°C for 48 hours - Measure the diameter of clear zones (zones of inhibition) using a ruler from two opposite directions - calculate mean of measurements - Calculate area of clear zones How would you measure the zone of inhibition? - correct answer Use a ruler to measure from a point on one side to a point directly opposite (with lid still in place) Measure again at 90° to first diameter measurementin order to calculate a mean Why should you not completely seal the agar plate? - correct answer To allow oxygen to enter the agar plate, preventing the growth of harmful anaerobic bacteria Why is it necessary to measure the diameter of the zone of inhibition twice? - correct answer Clear zones are not always uniform - taking more than one measurement allows a mean diameter to be calculated What equation is used to calculate the area of clear zones? - correct answer Area = πr^2 What is a source of error in this practical? - correct answer The area of the clear zone may be irregular and it is difficult to determine a suitable width to be recorded. CP06: PHOTOSYNTHESIS - correct answer ---