Investigating respiration in aged yeast

Authors Avatar

                                                                                                             Cosmina Oyolola GCSE C

Investigating respiration in aged yeast

Planning

AIM: I want to investigate respiration in aged yeast.

Prediction

I predict that the older the yeast, the smaller amount of carbon dioxide is given off.

Yeast (Saccharomyces cerevisiae) is a single celled micro-organism that belongs to the fungus group of plants, lives on the surface of fruits and feeds with sugar. It multiplies very fast by budding- each cell “pinches off” new ones and a large number can be formed in a short time. Yeast cells contain enzymes, this explains why the fermentation is taking place

Living yeast cells cause fermentation in the absence of air, converting sugar (glucose) to ethanol and CO2 . The respiration in absence of air is called anaerobic respiration (also known as fermentation). Anaerobic respiration is the breakdown of carbohydrates to release energy, without the use of oxygen.

Typical products of fermentation depend upon the substrate but can include organic acids (lactic acid, acetic acid), alcohols (ethanol, methanol, butanol), ketones (acetone) and gases (H2 and CO2)”

As yeast ferments glucose to ethanol, carbon dioxide is given off.

Glucose→ alcohol + carbon dioxide↑ + energy

At the beginning of the fermentation a bigger quantity of carbon dioxide is given off. Left for several days in a warm place the alcohol can be distilled off.

Apparatus

  • Conical flask with warm water- this is my water bath 250 ml
  • Test tube containing the glucose and yeast solution
  • Rubber cork connected to a plastic tube, that covers the test tube
  • Thermometer
  • Large plastic beaker
  • Measurement cylinder 50 cm3
  • Scale
  • Stop clock
  • Syringe 10ml

Method

My preliminary experiment worked very well, after I changed some parts of the apparatus and the temperature of the water bath. From my preliminary experiment I learnt that yeast works better at higher temperature; I tried the experiment at 21˚C and the yeast didn’t react, then I increased the temperature in the water bath to 39˚C and it started reacting, releasing carbon dioxide.

I also changed the conical flask- for the water bath- with a bigger one, to be able to keep the temperature constant for longer time.        

  • Measure with a syringe10 ml yeast dissolved in water solution
  • Put the content in a test tube
  • Weigh 3g of glucose and I add it to the yeast in the test tube
  • Stir it well so the glucose dissolves completely
  • Put the test tube in a water bath in the conical flask
  • Cover the test tube with a rubber cork that is connected with a plastic tube
  • Put the plastic tube in a measurement cylinder of 50 cm3 that is full with water
  • Put the measurement cylinder, upside down, in a large plastic beaker with water and make sure that there is no air in the measurement cylinder
  • Check the plastic tube inside the cylinder and make sure that is deep enough, so no carbon dioxide escapes in the plastic beaker
  • Start the stop-clock and register the time
  • Register the water bath temperature and keep it constant by adding warm water if the temperature drops
  • Read at the bottom of the meniscus to find out the volume of carbon dioxide released
Join now!

To be able to collect valid data I’ll measure everything very well and I’ll be careful not to make mistakes; if I suspect that something is not exactly the amount needed, or the temperature required, I’ll check again and make all the adjustments necessary.

I’ll record the time when the yeast starts reacting very precise, with the stop watch, writing down the minute and the second, as well as the other intermediate readings at: 0.50 cm3, 2 cm3, 5 cm3 8 cm3, 9 cm3 and 10 cm3. I chose these intermediate readings because it will be easier to register the ...

This is a preview of the whole essay