2. Name: Rhea Singh
Partners: Simon Lu and Kanami Watanabe
Date of experiment: 18-22 October, 2010
How Water Affects The Growth of Yeast
Aim: The aim is to see how putting different amounts of water affects the growth of
yeast.
Hypothesis: The more water we add, the more the yeast will grow. This will happen
because alcohol is a poison and it doesn’t help the yeast grow, but water is not a poison,
so maybe it will help the yeast grow. There is a chance that it might grow more because
by putting sugar which has energy in it, adding more water to it might help it grow more.
Variables:
Input variable: Change the amount of water that will be put in the sugar and
yeast. Adding more or less water will change it. First, start of by having 100ml of
water. Then test one with 200ml of water. Then test one with 50ml of water and
see the differences.
Output variable: Measure how much the yeast has grown. Measure it by
connecting a gas collection tube with the beaker that contains the yeast, water and
sugar, and then checking how much carbon dioxide is in the gas collection tube,
so that it will tell us how much the yeast has grown.
Control variables:
Control variable 1: The amount of yeast will be kept the same. Keep it
the same by putting the same amount of yeast (approximately 1 to 1.5g)
every time the experiment was conducted, so that the only thing that is
3. being changed is the water. Make sure to get the same amount each time
by weighting it every time on the measuring scale.
Control variable 2: The amount of sugar will be kept the same too. Keep
it the same by once again putting the same amount of sugar
(approximately 5g) every time the experiment is being conducted. Once
again weight it so that the same amount is being used.
Control variable 3: The amount of time when we measure how much the
yeast has grown will be kept the same too. Keep it the same by checking
each experiment trial after 15 minutes on how much the yeast has grown.
Materials:
250ml beaker; 100ml beaker; 1 measuring scale; 30g packet of yeast; a packet of sugar; 1
gas collection tube; 1 rubber stopper; water (not tape water and the temperature of it
should be approximately 30ºC); paper towels; paper; pen
Diagram:
Diagram 1: Here is a picture on how to set-up the experiment.
Method:
1. Set up equipment as shown in Diagram 1
2. Then take a packet of yeast and measure out 1g of yeast on the measuring scale.
3. After that, put it in the beaker using a tissue paper.
4. 4. Then, take a packet of sugar and measure out approximately 5g of sugar on the
measuring scale.
5. Take the 5g of sugar and put it in the beaker using a tissue paper.
6. After that take another beaker and fill it up with approximately 100ml of water.
7. Then take the water and put it in the beaker with the yeast and sugar.
8. Mix it all up and then wait for 15 minutes.
9. After 15 minutes, record how much the yeast has grown in your date table.
10. When you’re done with that, clean everything up.
11. Now do steps 1-5 again.
12. Then take another beaker and fill it up with approximately 200ml of water.
13. Then do steps 7-11 again.
14. After that take another beaker and fill it up with approximately 50ml of water.
15. Now do steps 7-10 again.
16. By now, information should have been recorded for 3 different trails (50ml,
100ml, 150ml). Now do steps 1-15 again for another 2 tries for accuracy in the
information.
Results:
TABLE:
How much the yeast has grown in 15 minutes:
AMOUNT OF TRAIL 1 (cmÚ) TRAIL 2 (cmÚ) TRAIL 3 (cmÚ) AVERAGE
WATER (ml)
50 19 19 -- 19
100 8 10 13 10.33
200 7 4 11 7.33
GRAPH:
5. Conclusion:
By doing this experiment, the results say that the more the water in the beaker, the less
the yeast will grow. Overall use three different amounts of water and try doing each trial
three times each for accurate information. Trial 1 said that 50ml of water made the yeast
grow 19cm; 100ml made it grow 8cm and 200ml made it grow 7cm. The difference
between 100ml and 200ml isn’t very much but the difference between those and 50ml of
water is a lot more. When doing everything for the second time, the results showed that
50ml of water made the yeast grow 19cm again, but 100ml made it grow 10cm and
200ml made it grow 4cm this time. There is a difference between those because the
beaker with 100ml of water grew 2cm more than before and 200ml of water made the
yeast grow 3cm less. After testing how much the yeast grows in 100ml and 200ml of
water for a third time, the results showed that for 100ml of water, the yeast grows 13 cm
and for 200ml it grows 11cm. This information is not the same as the other information,
but it still tells that the more the water, the less the yeast grows. The hypothesis was “the
more the water, the more the yeast will grow.” It is proven now that it is incorrect
because looking back at the information it looks like the less the water, the more the yeast
grows. So that means it's the opposite of what was thought to happen. A pattern that was
a little noticeable was that every time the experiment was conducted, the data didn’t
change too much. It was usually just around the same number range. The data is reliable
because it didn’t just test the theory once, but it tested it approximately three times, which
made the data more reliable. Some difficulties with this experiment were getting the right
and same amount of substances all the time for all the tests. If this experiment were to be
conducted again, then using a shorter period of time to finish the experiment would be
better. This is because then the information would be more reliable since the experiment
would have more trials.
Evaluation:
6. The information was very much reliable because the method wasn’t just tested out once,
but it was tested out three different times.
While doing this experiment, some errors appeared in the method. The first one was that
measuring the yeast for only 5 minutes changed to 15 minutes, because 5 minutes wasn’t
enough time to collect CO2 so the CO2 levels were low and hard to determine. By
changing it to 15 minutes, our information showed that we were able to collect more
CO2.
The second change that was made to this experiment related to the temperature of water.
At first it was decided that room temperature water will be used, but then it got changed
to using water with the temperature of 30°C. Yeast grows better in warmer water because
then the molecules can find the sugar faster, so it was decided that 30°C temperature
water will be used. By changing the water to 30°C, the data was more constant and more
reliable.
The last change made was from doing each method 3 times to doing it 2 times. This
happened because the amount of time that was given was too short. By working slower
than expected, doing the 50ml method 3 times wasn’t possible, which led to the data not
being entirely reliable.
To improve this method so that the data is more reliable, trying to make sure the same
amount of yeast and sugar is put in, because sometimes it was a bit more or less, and
maybe that interfered with the data a little. If this experiment were to be done again, the
probably changing the time of how much the yeast has grown from 15 minutes to maybe
10 minutes would also work. If this experiment was to be done again, then maybe
changing the amount of yeast put in the beaker could lead to new information about the
growth of yeast. Also changing the amount of sugar would work. These are all just some
ways on how this experiment could be done differently. Next time to improve this
experiment, focusing on all the weaknesses would get us more reliable information.
