AQA GCSE Combined Science Biology Required Practicals

Paper 1 biology Required Practicals

how do you conduct the microscope practical

• Place a thin slice of specimen (e.g. onion) on a microscope slide.

• Add a few drops of iodine solution (stain).

• Carefully place a cover slip on top.

• Observe under microscope using low power, then high power.

• Draw what you see with a pencil and label.

what is the independent variable of the microscopy practical

The specimen being observed (e.g., onion cells).

what’s the dependant variable of the microscopy practical

What you see – the cell structures.

what are the control variables of the microscopy practical

• Same stain used

• Same microscope magnification

• Same thickness of specimen

what are the limitations to the microscopy practical

• Limited resolution under light microscope

• Might squash cells when placing cover slip

common errors made in the microscopy practical / tips for exam questions

• Don’t use pen for drawing

• Label structures like cell wall, membrane, nucleus

• Use scale if provided

how do you conduct the osmosis in potato practical

• Cut equal-sized potato cylinders.

• Measure their mass.

• Place them in sugar solutions of different concentrations.

• After 30 minutes, remove and blot dry.

• Re-weigh each cylinder and calculate % change in mass.

whats the independant variable of the osmosis practical

Concentration of sugar solution.

what’s the dependant variable of the osmosis practical

Change in mass of potato.

what are the control variables of the osmosis practical

• Time in solution

• Temperature

• Volume of solution

• Potato size/initial mass

what are the limitations of the osmosis practical

• Inconsistent drying can affect mass

• Variation in potato tissue

what are common errors of the osmosis practical / tips for exam questions

• Always calculate percentage change

• Expect mass to increase in dilute solution, decrease in concentrated

how do you conduct the food tests practical

• Mix amylase, buffer, and starch in a test tube.

• Use water bath to control temperature.

• Take samples every 30 seconds and test for starch using iodine.

• Record how long it takes for starch to be broken down.

what is the independent variable of the food tests

Temperature.

what is the dependant variable of the food tests

Time taken for starch to break down (no colour change with iodine).

what are the control variables of the food tests

• Volume and concentration of starch and amylase

• pH (buffer used)

• Same interval for testing

what are the limitations of the food tests practical

• Hard to judge exact time of colour change

• Heat loss from tubes if not insulated