AQA GCSE Biology Paper 1 Required Practicals Graded A

AQA GCSE Biology Paper 1 Required Practicals Graded A How would you perform Required Practical 1 about microscopy? Place the prepared slide onto the stage Then select lowest power objective lens and slowly turn the coarse focussing dial When the objective lens almost touches the slide ,stop turning the dial Now look down through the eyepiece and slowly turn the coarse focussing dial until the cells come into focus Then use the fine focussing dial to bring the cells into a clear focus calculate total magnification Finally select a higher power objective lens, adjust the fine focussing dial and sketch the cells How do you prepare a slide? Place the specimen onto slide Add two drops of iodine Place cover slip over stained specimen Why is iodine put on the slide? It stains the cell so parts can be seen under a microscope How do you calculate total magnification? eyepiece lens x objective lens How do you calculate magnification? Image size/actual size What is the purpose of the coarse focussing dial? It is used to move the objective lens towards or away from the specimen What is the purpose of the fine focussing dial? Used to fine tune the focus on the specimen Used to focus on various parts of specimen Why would you look at the microscope from the side when adjusting the object lens position? Because there is a risk of damaging the slide if you look through the eyepiece How would you perform Required Practical 2 about culturing microorganisms? First clean bench with disinfectant solution Next sterilise an inoculating loop by passing it through a Bunsen burner flame Then open a sterile agar gel plate best a Bunsen burner flame and use the loop to evenly spread bacteria over the plate Next place sterile filter discs containing antibiotic onto the plate Finally incubate the plate at 25°C for 48 hours Why is the bench cleaned with disinfectant solution? To kill microorganisms that could contaminate the culture Why is the agar gel plate opened near a Bunsen burner flame? The flame kills bacteria in the air Why is the plate incubated at 25°C? Higher temperatures increase the risk of growing harmful pathogens What is the independent variable for the culturing microorganisms practical ? Antibiotic disks What is the dependent variable for the culturing microorganisms practical ? Area of the zone of inhibition What are the control variables for the culturing microorganisms practical ? Incubation temperature, same agar gel plate What is the method for performing Required Practical 3 about the effects of osmosis? Firstly peel potato skin and use a cork borer to produce 3 cylinders of the potato Then measure the length and mass of each cylinder using a ruler and a balance Next place each cylinder in a test tube and add 10cm³ of a 0.5 molar sugar solution to the first test tube, 10cm³ of 0.25 molar sugar solution to the second and 10cm³ of distilled water to the third. Leave the potato cylinders overnight to allow osmosis to take place Then remove the cylinders and gently roll them on paper towel Finally remeasure the length and mass of the cylinders and compare results Why is the potato skin peeled? It can affect osmosis Why is distilled water used? It contains no dissolved substances(normal water does) and di