Bio Lab Report Guide

DESIGN:

Research Question

What effect does varying the alcohol concentration of yeast have on its fermentation?

Introduction

Fermentation is the stage during which most CO2 is produced. When no oxygen is available, yeast will switch to an alternate metabolic pathway utilizing sugars for energy and producing, primarily, CO2 and ethanol. Yeast divides rapidly in this phase, reaching its carrying capacity (about 50 million cells/ml) in the wort, or must, and remains suspended in solution in order to expose maximum surface area to nutrients. Assuming no oxygen is added back to the fermenting wort, yeast will continue fermentation until one of two things happen - either alcohol concentration will exceed tolerance, or yeast runs out of food. 1

Figure 1 Process of Glycolysis and Anaerobic cell respiration in Yeast

Hypothesis

It is predicted that the fermentation of yeast will decrease with the increase in the concentration of alcohol because the alcohol concentration goes above the yeast cell’s tolerance and hence, the yeast cells die. Also, alcohol denatures the enzymes responsible for the break down of simple sugars i.e the food supply of yeast, as a result of which the yeast cells die.

Variables

INDEPENDENT DEPENDENT CONTROLLED Concentration/volume

of alcohol (in ml) Rate of fermentation

(in number of CO2

bubbles released) Temperature of alcohol

and water in the beaker

(in 0C) Volume of yeast +

glucose solution in the

bottle (in ml) Time duration of the

experiment (in minutes)

Manipulation of variables

Independent – Concentration/ volume of alcohol (in ml)

The concentration of alcohol is changed to observe its effect on the rate of fermentation of yeast. In this case, the concentration is measured in ml. The different concentrations of alcohol taken into consideration are – 0ml,

Bibliography: 1. Allott, Andrew. "The Chemistry of Life." IB Study Guides - Biology for the IB Diploma. 2nd ed. Oxford UP, 2007. 20. Print. In an experiment, the independent variable is the variable that is varied or manipulated by the researcher, and the dependent variable is the response that is measured. An independent variable is the presumed cause, whereas the dependent variable is the presumed effect. The IV is the antecedent, whereas the DV is the consequent. In experiments, the IV is the variable that is controlled and manipulated by the experimenter; whereas the DV is not manipulated, instead the DV is observed or measured for variation as a presumed result of the variation in the IV. "In nonexperimental research, where there is no experimental manipulation, the IV is the variable that 'logically ' has some effect on a DV. For example, in the research on cigarette-smoking and lung cancer, cigarette-smoking, which has already been done by many subjects, is the independent variable." (Kerlinger, 1986, p.32) When reseaerchers are not able to actually control and manipulate an IV, it is technically referred to as a status variable (e.g., gender, ethnicity, etc.). Even though researchers do not actually control or manipulate status variables, researchers can, and often do, treat them as IVs (Heppner, Kivlighan & Wampold, 1999). "The DV refers to the status of the 'effect '(or outcome) in which the researcher is interested; the independent variable refers to the status of the presumed 'cause, ' changes in which lead to changes in the status of the dependent variable…any event or condition can be conceptualized as either an independent or a dependent variable. For example, it has been observed that rumor-mongering can sometimes cause a riot to erupt, but it has also been observed that riots can cause rumors to surface. Rumors are variables that can be conceived of as causes (IVs) and as effects (DVs)." (Rosenthal & Rosnow, 1991, p. 71)