required practical 9

to measure the rate of oxygen uptake by an organism, which can be used to estimate rate of respiration

• to be sure that changes in volume are only due to O2 absorption • if CO2 weren’t absorbed there wouldn’t be a change in volume and therefore presure in the test tube, so the liquid in the manometer wouldn’t move

so the system is airtight to ensure no gases enter and leave

• the volume of gas decreases in the experimental tube - O2 diffuses into the organism for respiration, and the CO2 produced is absorbed by the chemical • this causes a decrease in pressure in the experimental tube • the pressure is comparatively higher in the control tube than the experimental tube, so the liquid moves towards the experimental tube

rate = volume of O2 absorbed/time x mass of organism volume of O2 = volume of manometer = πr^2 x length (distance moved by liquid) units have three components for volume, time and mass

investigate the effect of a named variable on the rate of respiration of cultures of single-celled organisms

• set up a water bath at 35 degrees • label 5 test tubes 1 to 5 • shake the yeast and glucose mixture • add 2cm3 of the yeast and glucose mixture to all five tubes • place the five tubes and the methylene blue indicator in the water bath and leave them until their contents reach 35 degrees • add 2cm3 methylene blue to test tube 1 • immediately shake the tube for 10 seconds and replace it in the water bath (note the time) • record how long it takes for the blue colour to disappear in the tube • repeat these steps for the other four tubes • repeat these steps to obtain data or 25 degrees

it accepts the electrons which move down the electron transport chain in oxidative phosphorylation