Biology Core Practicals

Daphnia Heart Rate experiment - select daphnia - use strands of cotton wool to trap daphnia on microscope slide - use filter paper to absorb the water around the flea - place daphnia in the middle and put a few drops of water over it so it can survive - locate daphnia's heart - set up stop clock and count the number of beats per minute - repeat with different caffeine concentrations instead of water Daphnia control variables - temperature - size of daphnia (or age and gender) Daphnia independent variable - caffeine concentration Daphnia dependent variable Heart rate Daphnia risk assessment Daphnia contaminating you, so wash your hands after Daphnia ethics They may feel pain Vitamin C content experiment - transfer 1cm3 of DCPIP into a test tube with a pipette - titrate vitamin c solution drop wise into DCPIP and swirl gently - record volume of vitamin c needed to decolourise the blue DCPIP - repeat the experiment with different concentrations of DCPIP Define control variable The unchanged variable in an experiment. It is used to compare to your experimental results Define independent variable The variable that is changed in the experiment Define dependent variable The variable that you measure Vitamin C content risk assessment 1/3 - spilling DCPIP can cause irritation to eyes and skin so wear lab coat, gloves and goggles - soak beetroots in water - cut beetroot into equal sizes and weigh so its the same mass - place in test tubes and fill with 10cm3 of water Alcohol on Membrane Permeability ex- - wait 15 minutes for colour to leak out of periment beetroot - obtain a sample of water surround beetroot - place in a cuvette and zero the colorimeter - measure the absorbance of the liquid What does a higher absorbance value mean? A higher pigment concentration, so a more permeable membrane Why does the permeability of a cell mem- Higher alcohol concentrations will disbrane increase as alcohol concentration rupt the phospholipid bilayer more, causincreases? ing more/bigger gaps - soak beetroots in water - cut beetroot into equal sizes and weigh so its the same mass - place in test tubes and fill with 10cm3 of water - place test tube in different water baths Temperature on Membrane Permeability at different temperature ranger experiment - wait 15 minutes for colour to leak out of beetroot - obtain a sample of water surrounding the beetroot - place in a cuvette and zero the colorimeter - measure the absorbance of the liquid Why does membrane permeability increase as temperature increases? Higher temperatures cause proteins in the membrane to denature as their tertiary structure is damaged, creating 2/3 more gaps in the phospholipid bilayer so more molecules can pass through Because phospholipids have little energy Why does membrane permeability de- and are packed closer together, making crease as temperature decreases? the membrane rigid, causing less molecule to be able to pass through Risk assessment of temperature on membrane permeability Hot water can burn you so if burned run hand under tap Scalpel can cut you, so cut away from your body and if cut, apply pressure Risk assessment of alcohol on membrane permeability Alcohol is irritant and flammable so wear eye protection and keep away from open flames Scalpel can cut you, so cut away from your body and if cut, apply pressure 3/3