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A-level Aqa biology required practicals summary
Summary of all the practicals, with answers taken from mark scheme
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Bio Practicals Summary1: Enzymes
- Control temperature/pH unless measuring the effect of it, control volume and concentration
of enzyme & substrate solution.
- Describing curves: say what happens at start/middle/end- more kinetic energy, more E-S
complexes form so higher rate. Flattens due to temp too high, denatured enzyme(active sit
changes shape so substrate no longer complementary) or if not temp, all substrate has been
used/active sites are full.
- Curves level at same value – all substrate changed into product, same amount of product
formed as initial substrate conc.
2: Squashed root tips & microscope
- Tissue has to be thin to allow more light through so single layer of cells is viewed (reason
coverslip is pressed down firmly)
- Add stain to make chromosomes visible
- Placed root tip in HCL- kill cells and macerate tissue
- To ensure mitotic index is accurate: examine large fields of view to ensure sample is
representative
3: Water potential
- Use calibration curve to determine conc when there’s no change in mass
- Sometimes bungs placed in tubes to prevent water from evaporating and changing WP of
solution
- Repeat experiment to calculate mean and outline/reduce anomalies
- Keep in solution for same amount of time as it’s a controlled variable- allows time for
osmosis to be complete
4:Ethanol conc on permeability of membrane
- Control water volume as if too much, could make solution lighter and more light passes
through
- Increase in temp of water damages membrane because membrane proteins denature so
more pigment can pass through
- Phospholipids dissolve in ethanol so membrane dissolves
- Put tubes with beetroot into water bath to control temp as it affects diffusion
5:Dissection
- Scientific Drawing- don’t shade, add labels but don’t let them cross lines, add magnification
scale bar
- Wash hands/wear gloves/wear goggles/dispose in separate bin/disinfect to prevent cross
contamination – cut away from fingers
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