Biology Practicals - AQA A level - 2022

what are variables must be controlled in an investigation into the effect of temperature on the rate of an enzyme controlled reaction? (RP1) Enzymes - Answer - • PH • concentration of substrate • concentration of enzyme describe the method for investigating and measuring the effect of temperature on the rate of an enzyme controlled reaction (RPI) Enzymes - Answer - 1. make 2 control test tubes containing 5cm of milk in each • 1 with 5cm of water - no enzyme activity • 1 with 5cm of HCL - completely hydrolysed sample 2. make 4 test tubes with 5cm of milk and use a buffer to ensure equal PH 3. add to water bath for 10mins to equilibrate temp first 4. Add 5cm of trypsin (enzyme) to each tube and record mean time it takes for milk to be hydrolysed 5. repeat step 4 at different temps (20.,30,40,50ºC) 7. work out the rate of reaction and plot a graph of RoR/temp what is equation for the rate of reaction for RP1? - Answer - rate of reaction = 1 ÷ mean time how do you measure uncertainty in your readings? - Answer - take half of the unit of the last decimal place in a measurement, and add/minus that from both sides describe the method for preparing a root tip cell squash (RP2 part 1) Cells - mitosis - Answer - 1. heat 1 mol dm⁻³ HCL at 60ºC in a water bath (to equilibrate) 2. cut small sample of root tip using a scalpel 3. transfer root tip to boiling tube of HCL and incubate for 5mins 4. use tweezers to remove root tip from tube and rinse with cold water • leave to dry on paper towel 5. place root tip on microscope slide and remove 2mm from the tip 6. add a few drops of stain to make chromosomes visible 7. lower coverslip carefully onto the slide and push down firmly to squash the tissue (makes tissue thin to allow light to pass through) • ensure there are no air bubbles which may distort the image • don't smear coverslip sideways as this could damage the chromosomes describe how to use a micro