Exponential (log) Phase - Lag phase is followed by log phase during which budding (asexual reproduction) occurs. Yeast cells start multiplying exponentially, doubling in number each time they reproduce.
Stationary phase - Exponential growth cannot be continued forever in a boiling tube because as more and more yeast are competing for dwindling food and nutrients, exponential growth stops. The rate of cell growth (division) is exactly balanced by the rate of cell death.
Death Phase - Stationary phase, in a standard bacterial growth curve, is followed by Death Phase. At this phase, yeast run out of nutrients and the toxic waste content gets too high toxins. The yeasts are not able to grow in this kind of environment. So they die off.
Diagram for lad log death phase
Fructose and glucose are both simple sugars so they do not need to be broken down. They have the same molecular formula, C6H12O6, but have different structures. Glucose is recognized by having a 6-member ring and having six carbons, a hexose. Although fructose is a hexose (6 carbon sugar), it generally exists as a 5-member ring . Because of that structure, fructose take more steps of conversion of sugar to energy than glucose during respiration. Therefore I expect population of yeast will grow fastest in solution containing glucose.
Sucrose is a disaccharide so it will be much easier to broken down into monosaccharides to used for respiration than polysaccharide starch.
Apparatus
Test tube rack
5 Boiling tubes
1ml Pipette
Glass stirrer
Label Marker pen
Label sticker
10 ml measuring cylinder
Haemocytometer with cover slip
Microscope
Yeast solution
Glucose solution
Fructose solution
Sucrose solution
Starch solution
Water
Cotton ball
Method
1. Set up 5 boiling tubes in a test tube rack.
2. Label each boiling tube with a number. 1, 2, 3, 4, 5. All boiling tubes except boiling tube 5, will be added yeast, sugar and water. Boiling tube 5 will not be added sugar, to see as a control experiment, in order to see whether sugar have an effect on growth of yeast population.
3. Fill each boiling tube with 1 ml of yeast solution by 1ml piptte.
5. Pour 9ml of glucose in boiling tube 1.
Pour 9ml of fructose in boiling tube 2.
Pour 9ml of sucrose in boiling tube 3.
Pour 9ml of starch in boiling tube 4.
Pour 9ml of water in boiling tube 5.
6. Use a clean stirrer and thoroughly stir boiling tube 1 to stop yeast cells clumping together. Stirring of the solution in the boiling tube is required before sample solution is taken for counting in order to prevent yeast cells from clumping, so that it will be easier to count the number of yeast cells on B square. Otherwise, clumping can cause inaccuracy results in number of cells counting.
7. Count number of cells using haemocytometer under light microscope.
∙ Drop the sample from boiling tube 1 onto haemocytometer using clean pipette. Then cover the slide with a coverslip.
∙ Count the number of cells present in 5 type B square as indicated by the green colour.
∙ Count the cells that lie on the edge of top and right. Do not count the cells that lie on the edge of bottom and left. Use the tally counter for counting cells.
8. Another sample will be taken from the same boiling tube. The above procedure will be repeated. If there are anomalous results, the procedure will be repeated again.
9. Place a cotton ball on the opening of boiling tube 1 to stop contamination.
10. This procedure will be repeated for the other boiling tubes.
11. Samples and readings will be taken at regular intervals for the next 5 days. All the results will be recorded in a table.
12. After all results has been collected, I am going to carried out statistic test to whether the null hypothesis should be rejected or accepted.
Reasons for apparatus
Boiling tube
I chose this because it holds larger volume than a test tube.
Haemocytometer
This is most accurate way of measuring number of cells in the solution. It has a counting chamber which has a specific volume 0.1 mm3. So only small amount of sample will be taken out to measure, rather than measuring cell contents in the whole solution. Also simple calculation can be done to estimate the cells contents in whole solution in boiling tube since volume of sample is known.
Coverslip
The cover slip makes sure that correct volume is on the slide and it also prevents the objective lens from being immersed in the liquid.
1ml pipette
1 ml will be added to boiling tube so using 1 ml pipette will be more accurate way of measuring of required volume.
Calculation
There is 10 cm3 of solution in each boiling tube. Following calculation is as example that show how to find number of yeast in 10 cm3 of liquid.
1. Mean of yeast cells in 5 type B square
Say 1st reading – 52
2nd reading – 54
Add 52 and 54 and then divide by number of reading which is 2.
52 + 54= 106/2 = 53 yeast cells
So there are 53 yeast cells in 5 B type square
2.Find number of yeast in A type square
1 A square = 25 B square
so 5 * 53 = 265 yeast cells
Volume of A square is 0.1 mm3.
So 256 yeast cells in 0.1 mm3.
3. Find number of yeast cells in 1 cm3
1 cm3 = 1000 mm3
so 1000 * 265 =
4. Find number of yeast cells in 10 cm3
1 cm3 = 265,000 yeast cells
10 cm3 = 265000 * 10 = 2,650,000 yeast cells
Rate of yeast per day = total number of yeast in 5 days / time taken (5 days)
Standard deviation
∑ = sum of
n = the number of values
x = each value in data set
Graph that I am going to plot for my results
Number yeast again days ( all 5 different substrates on one graph for comparison)
rate of yeast growth against 5 different type of substrates
