Cool Yeast lab

The purpose of this lab was to conduct a study on cell communication. We did this by observing yeast mate and produce schmoos. Over several time intervals we observed the yeast both on a liquid base (sterile water) as well as on a dry base (dry Petri dish). These two surfaces were done to observe the effect they have on cell communication and their chemical signals. 

We labeled three test tubes as either alpha, A or mixed and put in the yeast cells respectively in each of the test tubes. Then we put two milliliters of sterile water in each test tubes to simulate wet environments. Then we added an equal amount of broth in each test tube in order to sustain their life overnight.  Then we left them in an incubator for 24 hours. After the 24 hours had elapsed we put samples of each test tube on a microscope slide and then counted the amount of yeast present.  

Below are the pictures we have taken of the yeast after 24 hours have elapsed:

Mixed (82 yeast are present)

Alpha (86)

A type (40 yeast were present)

Then we waited an additional five minutes for each of the test tubes. Below are the pictures of each test tube at the first time interval (5 minutes)

Mixed (39 were present)

Alpha (43 schmoos were present)

A type (95 schmoos were present)

Then we an additional five minutes and let the yeast culture. 

Mixed (231 schmoos were present)

Alpha (40 schmoos were present)

A type (5 schmoos were present)

 

As demonstrated by this lab, under the wet conditions, the A-type yeast alone went from 40 to 95 to 5 yeast cells. The alpha type went from 86 to 43 to 40 cells, and the culture of both A-type and alpha type cells went from 82 to 39 to 231 cells. Now in retrospect this data tells us very little because the yeast cells in each of the three cultures tended to vary up and down drastically. This error can be attributed to the fact that when we counted each yeast cell, we counted them from a field of view in the microscope, but not only were we onto always sampling the culture from the same exact place in the liquid, we also had no way of looking at the culture in the same place under the microscope. Theoretically, however, all three of the cultures should have increased in size. A type and alpha type should have reproduced asexually when separate, and when mixed, they should have reproduced sexually and moreso.

We also performed similar procedures to grow the yeast cultures under dry conditions. Three cultures were taken from the original test tubes (again A-type, alpha, and mixed) and allowed to dry onto an agar plate in a Petri dish. Then, as time progressed, we sampled the cultures and observed them under microscopes to determine how growth had occurred. Our results are pictured below.

At the beginning of the procedure, our dry cultures started out with the following numbers of cells.

Then at the first time interval, our dry cultures had the following numbers of cells.

At the last time interval, our dry cultures had these final numbers of cells.

As with the cultures grown under wet conditions, the ones grown under dry conditions should also have grown in a similar manner. That is, A-type and alpha type grow asexually when separated and sexually when together, and when they grow sexually, growth is greater than when the grow asexually.

Based on the data from both the wet and dry cultures, we can conclude that yeast cells grow best sexually under dry conditions. This can be attributed to the means by which yeast cells sexually reproduce.

For ease of description, Let's consider A-type and alpha type yeast cells to be like opposite genders, almost like male and female. Each gender releases a pheromone that physically attracts the opposite gender. It does this because it behaves as a ligand that stimulates the cell to change its chape and develop a shmoo that grows toward the location from which the opposite pheromone is coming. In order for the shmoo projection to grow out, the yeast cell must completely change its cytoskeletal structure, which reveals the true power of singalling molecules to really get work done. The shmoo is projected in the direction from which the opposite pheromone was produced, and the rest of the cell follows the projection toward the source. This allows the a and alpha type cells to grow toward each other, in order that they might sexually reproduce. Sexual reproduction is much more favorable for the yeast cells than asexual reproduction because it produces twice the amount of each type of cells. 

Bearing all this in mind, when we say that the yeast cells grow best under dry conditions, it's because the dry environment (as opposed to the liquid one) conducts these pheromones more effectively. And this kind of makes sense if we use an analogy. Colognes, perfumes, and body sprays were developed as a means to attract people. They behave in a similar manner as the yeast cells' pheromones, albeit certainly not so drastically, much to the chagrin of companies like Old Spice and Axe. If we were to spray the aerosol into an empty bucket of air and into a full bucket of water, we can probably guess that the dry bucket of air would conduct the scent better than the full, wet one.

Therefore, these yeast cells demonstrate the behavior of singalling moelecules and receptors and just how important and powerful they can be.