1-1 Yeast Growth

Investigation 1-1:

Population Growth Behavior

Conduct an experiment growing live organisms which are much, much smaller than goats. Determine whether or not this population behaves in much the same manner as a population of goats.

Mix 1 ml. of molasses solution prepared for you by your teacher, a pinch of dried yeast, and 9 ml water in a test tube. Grow for 24 hours. Observe and count all yeasts visible in the field of view under a microscope using a drop of yeast culture at 400X magnification. Continue to count cells every few days for 2 weeks. It may be necessary to use serial dilution to make yeasts easier to count. Graph the yeast population growth.

Serial dilution

Serial dilution

Serial Dilution may be achieved by diluting cultures before counting them:

Take 1 ml from a parent culture and add it to 9 ml distilled water. After mixing thoroughly, take 1 ml of culture from your diluted tube and add it to a 3rd tube containing 9 ml of distilled water. Mix thoroughly before counting. This gives a total of a 100-fold dilution. (Multiply your counts by 100 to get the original number of organisms).

Observe the appearance of the test tube and odors detected. Graph your yeast counts, and log your observations.

What has happened to the population of yeasts in the test tube?

Have the yeasts encountered limiting factors?

What might they be?