BioFuel Production through Yeast Fermentation Objectives The objectives of this lab exercise are for you to learn about the use of ethanol as an alternative energy source learn about the process of fermentation by yeast cells develop your ability to properly design an experiment and interpret the results improve your writing skills and use of literature sources Exercise Synopsis Week 1 have read assigned materials perform initial experiment Week 2 have read assigned materials we will discuss experimental design groups will plan out experiment and we will also have an Excel graphing session Week 3 have read assigned materials groups perform their experiment Lab report Introduction and Literature Cited due Week 4 Group work interpreting results drawing conclusions peer review of graphs completed graphs must be brought to lab Completed lab reports due two weeks later I Reading for Week 1 Before coming to lab for the first week of this lab exercise you should read the following introduction to biofuel production and review the basic experimental methodology Figure 1 The molecular structure of ethanol Biofuel refers most commonly to ethanol which is produced through the fermentation of carbohydrates by yeast cells Fermentation is an energy yielding process that cells carry out in the absence of oxygen Although fermentation does not provide much usable energy for the cell it is sufficient for yeast cells Yeast cells produce ethanol and CO2 as byproducts and the ethanol produced has become a valuable energy source There is much interest in ethanol as an energy alternative to fossil fuels which are nonrenewable and contribute significantly to Figure 2 World ethanol atmospheric pollution production Demirbas 2009 92 Ethanol which is blended with gasoline at about 510 to yield gasohol has several advantages over petroleum as an energy source The presence of an oxygen atom in ethanol Figure 1 allows gasohol to burn cleaner than regular gasoline with reduced emissions of carbon monoxide nitrogen oxides and hydrocarbons Ethanol also helps to address concerns about greenhouse gas emissions mainly in the form of CO2 Unlike petroleum ethanol is carbon neutral which means that the CO2 released when it is burned is balanced by the uptake of CO2 from the atmosphere by plants growing to produce more grain In light of its advantages world production of ethanol has increased dramatically in recent years Figure 2 Biofuel Production Page bp1 Nevertheless there are also reasons to be concerned about the increased reliance on ethanol From an energy balance perspective more energy may be invested in the production of ethanol harvesting of the crops transportation etc than it yields as a fuel for differing views compare Shapouri et al 1995 and Pimentel 2003 The need to divert food crops to fuel production also concerns many people A bushel of corn approx 56 lbs can yield approximately 2 5 gallons of ethanol and at a corn yield of 125 bushels per acre Shapouri et al 1995 an acre of farmland would yield enough corn for 310 gallons of ethanol Thus production of 8 billion gallons of ethanol requires about 2 5 million acres of land The World Watch Institute Gardner 2000 44 has reported that the amount of harvested farmed land in the world has declined over the last quarter century while over the same time period world population has increased 50 Thus committing agricultural land to energy production will have consequences on available food in a world where the majority of people live in poverty However it can also be argued that utilization of land to grow corn to feed to cattle is an inefficient use of the land if land grew crops for direct human consumption then roughly ten times as many people could be fed The ten percent rule is discussed in Biol 101 There are other ways of producing biofuel One is by using various plant materials unsuitable for human consumption For example the biofuel industry in Brazil uses sugar cane materials left over after sugar extraction This process does not take food out of the food chain Another approach being actively researched is the large scale culturing of algae to yield biomass as well as oils for biofuel production Variables that affect the rate of fermentation in yeast cells A scientist wishing to increase biofuel ethanol production might evaluate the effects of many different factors or variables on the rate of yeast fermentation There are many variables that could potentially affect the rate of yeast fermentation Indeed an infinite number of factors e g the alignment of the planets might potentially affect the outcome of an experiment however a scientist seeking to optimize biofuel fermentation must use judgment to decide which variables are most likely to significantly affect the process Some of the variables known to affect fermentation in yeast cells are described below Type of carbohydrate What are the rates of CO2 production when fermentation is allowed to proceed in the presence of glucose fructose lactose or sucrose Concentration of carbohydrate What is the effect of different concentrations of glucose on the rate of yeast fermentation Concentration of salt How does varying the salt NaCl concentration affect the rate of yeast fermentation Osmolarity Osmolarity refers to the total concentration of sugars or salts in the fermentation solution which affects water flow into or out of the cells What is the affect of adding sorbitol which cannot be utilized by yeast for fermentation along with glucose on the rate of fermentation Ethanol concentration What are the effects of varying the initial ethanol concentration in the fermentation mixture on yeast fermentation pH What is the effect of varying pH on yeast fermentation Biofuel Production Page bp2 Temperature What are the effects of different temperatures on yeast fermentation On the Biofuel Web Resource Page at http marietta edu biol introlab index105 html you will find further information about fermentation and these factors as well as a list of pertinent literature resources on reserve in the library How can we measure yeast fermentation Figure 3 Respirometer As grain will continue to be used for biofuel production it is appropriate that we should seek to maximize the yield of ethanol One way to do this is to study the effects of various factors on the rate of fermentation Ethanol and CO2 are produced by yeasts during fermentation the CO2 is what leavens bread and gives beer its fizz Although measuring ethanol