Investigating CO2 Production of Yeast

Objective

The experimental objective of this lab is to observe the effects of certain environmental conditions on the activity of microorganisms in a batch process. Activity will be determined by measuring production of carbon dioxide (CO_2) by rehydrated yeast in each batch and qualitative observations of the turbidity and buoyancy of the batch mixture. Predictions will be made regarding the effects of variables within the batch mixture on the yeast’s activity, and then be evaluated for validity after the batches are observed.

Overview

The use of yeast or other biological agents, such as proteins or recombinant DNA, to form useful products is an example of biotechnology. A growing field, biotechnology has led to a number of important scientific milestones; for example, in 2020, the scientists who discovered CRISPR-Cas9, an enzyme that allows gene editing, won the Nobel Prize. Their work has allowed for innovations in fields such as healthcare and agriculture. This lab provides an elementary introduction to biotechnology by investigating the reactions of yeast, a microbial fungal species commonly used to convert substrate into valuable products, like bread and alcohol.

Cellular Respiration

Yeast is a species of single-celled fungus. Fungal cells, like plant and animal cells, are eukaryotic; they contain membrane bound organelles and genetic material (Deoxyribonucleic acid, or DNA) stored within a nucleus. Cells must perform many different functions to survive, including the synthesis of proteins, the removal of waste products, and the regulation of internal conditions or homeostasis. These functions require energy obtained from the chemical energy stored within molecules consumed by the cell as food (also called substrate).

An important function is cellular respiration, which is the conversion of the substrate molecule to usable energy, a crucial portion of the cell’s metabolism. The basic reaction for cellular respiration is the conversion of the simple carbohydrate glucose (C_6H_12O_6) into carbon dioxide and water by reacting it with oxygen, and in the process releasing its chemical energy used generate the cell’s energy storage molecule Adenosine Triphosphate (ATP) as see in equation (1).

$C_{6}H_{1}2O_{6}+6O_{2}\rightarrow 6CO_{2}+6H_{2}O+ATP(1)$

In this lab, respiration will be monitored by measuring the amount of CO_2 produced from yeast and table sugar in warm water.

Batch Processes

In lab and industrial settings, cellular respiration often takes place in a reactor known as a batch reactor, where the yeast is placed in a sealed vessel containing a reaction medium and some substrate. Environmental conditions can impact the rate of the reaction and the total amount of product produced. In this experiment, a beaker will serve as the batch reactor, water will be the medium, and the substrate will be sugar. Six batch conditions will be investigated (Table 1). In the first batch, a control experiment will provide a baseline measurement of the yeast behavior in warm water. In the second batch, table sugar will be introduced. In the third, fourth, and fifth batches, the medium will be altered by adding vinegar, soap, or salt to the solution. Last, an alternative substrate, Splenda, will be investigated.

Table 1: Batch Conditions

Condition	Substrate	Medium
1	None	Water
2	Table Sugar	Water
3	Table Sugar	Water + Vinegar
4	Table Sugar	Water + Salt
5	Table Sugar	Water + Soap
6	Splenda	Water