practicals

• respirometer diagram
• why does the respirometer apparatus have to be airtight? to prevent air entering or leaving as this would change the volume and therefore the pressure, affecting the movement of the coloured liquid
• what is the purpose of the soda lime in the respirometer? to absorb the carbon dioxide produced in respiration so the volume of oxygen absorbed by the organisms can be measured
• why does the liquid in the manometer move towards the tube with the respiring organisms in the respirometer? - the respiring organisms take in oxygen from the air in the experimental tube - the carbon dioxide produced in respiration is absorbed by the soda lime - so the volume of gas in the experimental tube decreases, decreasing the pressure in the experimental tube - the pressure in the experimental tube is comparatively lower than the control tube - so the coloured liquid moves down the pressure gradient towards the experimental tube
• units for rate of respiration unit for vol, per unit time, per unit mass e.g. cm3 min-1 g-1
• how do you calculate rate of respiration from distance moved by coloured liquid, time, diameter of manometer and mass of organisms in experimental tube? volume of cylinder = pi x r2 x length rate = volume / (time x mass)
• why is the respirometer submerged in a water bath? to provide the optimum temperature for the organisms and therefore the optimum temperature for the enzymes involved in their respiration
• what is the difference between the control and experimental tube in the respirometer? the organisms are substituted with glass beads of the same mass in the control tube
• why is the tap left open for 10 minutes + the syringe removed? to allow for the apparatus to equilibriate, accounting for any expansion that might cause the pressure to change inside to allow for the respiration rate of the woodlice to stabilise to their new environment
• why is the syringe used to reset the manometer? so the ends of the fluid are at the same level on either side of the 'U
• how do you check the precision of the respirometer results? repeat + calculate mean oxygen volume
• limitations of respirometer experiment (2) animal may be distressed, falsifying results implications for animal welfare
• alternative to soda lime pellets in respirometer KOH (potassium hydroxide)
• independent variable in respirometer organism used OR temp of water bath
• dependent variable in respirometer change in volume of gas in cm3
• control variables in respirometer organism/temp (depending on IV) pressure mass of tissue
• 2 reasons why the respirometer should be placed in a thermostatically controlled water bath - respiration is controlled by enzymes - the rate of an enzyme controlled reaction is affected by temperature
• what modifications to the respirometer equipment would you make if the organism was a plant? stop photosynthesis by placing apparatus in the dark
• at the end of the respirometer experiment, why might the liquid not move if the organisms were still respiring? anaerobic respiration does not require oxygen so no pressure drop in tube
• function of roll of filter paper in respirometer increases SA of air in contact with KOH and speeds up absorption of carbon dioxide
• how could the respirometer syringe be checked for leaks? syringe pressed down, changing level of coloured oil if there are leaks present the oil will gradually return to the original level
• give another function of the syringe in the respirometer reset the oil droplet to allow readings over longer time period
• formula for calculating respiratory quotient vol CO2 produced / vol O2 consumed
• what is the Hill reaction? when photoionisation releases electrons that are picked up by coenzyme NADP, along with H+ ions from photolysis, forming reduced NADP
• how do we study the rate of the Hill reaction? using indicators such as DCPIP when present these indicators accept the electrons instead of NADP this causes blue oxidised DCPIP to change colour to colourless reduced DCPIP rate of the Hill reaction = rate at which indicator changes colour
• what is the role of dehydrogenase in the Hill reaction? catalyses uptake of electrons by NADP/DCPIP
• in the DCPIP practical, why do you grind up the leaves? to break apart the tissues
• in the DCPIP practical, why do you grind the leaves in isolation solution? prevents cell damage due to osmosis or extreme pH
• in the DCPIP practical, why do you filter the liquid with muslin? removes large pieces of leaf tissue
• why does adding ammonium hydroxide slow the rate of DCPIP decolourisation? ammonium hydroxide ions compete to accept electrons so electron transfer across the ETC to DCPIP is slowed so it is reduced less quickly
• in the DCPIP practical, what is the purpose of the tube containing DCPIP, water and chloroplast suspension wrapped in aluminium foil? to show photosynthesis does not occur and DCPIP does not decolourise when there is no light
• in the DCPIP practical, what is the purpose of the tube containing DCPIP, water and isolation medium? to show photosynthesis does not occur and DCPIP does not decolourise without chloroplasts
• in the DCPIP practical, what is the purpose of the tube containing water and chloroplast suspension? to act as a reference for when DCPIP is completely decolourised
• in the DCPIP practical, what is the purpose of the tube containing DCPIP, water, chloroplast suspension and ammonium hydroxide? to show DCPIP decolourises slower with ammonium hydroxide
• in the DCPIP practical, what is the purpose of the tube containing DCPIP, water, and chloroplast suspension? to show DCPIP decolourises faster without ammonium hydroxide