Effects of Sucrose Concentration On Cell Respiration In Yeast

Topics: Cellular respiration, Carbon dioxide, Glucose Pages: 10 (2192 words) Published: July 26, 2015
Effects of Sucrose Concentration On Cell Respiration In Yeast


This lab investigates the effects of Sucrose concentration on cell respiration in yeast. Yeast produces ethyl alcohol and CO2 as a byproduct of anaerobic cellular respiration, so we measured the rate of cellular respiration by the amount of CO2  produced per minute. The results show a trend wherein increased concentrations of sucrose increase the rate of cellular respiration. Introduction

All living cells require energy in order to proceed with cellular processes such as active transportation, and the synthesis of molecules. ATP (Adenine Tri-Phosphate) is a molecule, which provides energy in a form that cells can use for such cellular processes. Cellular respiration is the process in which cells produce this energy to survive. It occurs in the mitochondria of the cell and is is vital for the survival of most organisms because cells cannot use the energy in glucose until it is stored in ATP. In the presence of oxygen, organisms can respire aerobically. The balanced chemical equation for aerobic respiration is:

C6H12O6 + 6O2 -> 6 CO2 + 6 H2O + ~ 36-38 ATP

In the process of aerobic respiration, C6H12O6 is first broken down into 2 3-Carbon molecules called pyruvate or pyruvic acid through the process of Glycolysis, which literally means, “Sugar decomposition.” A net of 2 ATP is produced during Glycolysis. When oxygen is available, these 2 pyruvates move on to the Krebs cycle and electron transport chain to produce the remaining 34-36 ATP. Fig 1.1: An overview of Aerobic Cell Respiration (http://www.phschool.com/science/biology_place/biocoach/images/cellresp/glucover.gif)

 In the process of anaerobic respiration, C6H12O6 is also broken down into 2 pyruvates through the process of Glycolysis. However because oxygen is unavailable, instead of the Krebs cycle and the electron transport system occurring, fermentation occurs —Lacate fermentation in animals, or Alcoholic Fermentation in yeast. Like in aerobic respiration, the co-enzyme NAD+ will need to keep re-generating to continue making ATP in anaerobic respiration. Unlike aerobic respiration however, NAD+ is regenerated by alcoholic fermentation in anaerobic respiration in yeast, producing ethyl alcohol— which is also known as ethanol or C2H5OH, the same form of alcohol used in alcoholic beverages such as beer—and CO2

. The formula for anaerobic respiration in yeast is:

C6H12O6->> 2 CH3CH2OH+2CO2 + 2 ATP

Yeast is a facultative anaerobe, meaning that its cells are able to make ATP through aerobic and anaerobic respiration (Shimomura-Shimizu, 2009). This experiment explores the effect of varying sucrose concentrations on the rate of anaerobic cell respiration in yeast. Hypothesis

Yeast is a facultative anaerobe— meaning that it is capable of making ATP by aerobic respiration when Oxygen is available, but can also switch to aerobic respiration when it is not— so it will first respire aerobically until the test-tube is sealed with the rubber stopper. The rubber stopper with the measuring mechanism (an airline tube with one end attached to the hole of the rubber stopper and the other end joined to a syringe, or simply a gas syringe) will stop the in-flow of air, forcing the yeast to respire anaerobically after all the oxygen in the airtight test-tube has been used up. The amount of carbon dioxide gas produced reflects the rate of cell respiration  because CO2 is a byproduct of anaerobic cell respiration in yeast (as well as ethyl alcohol). So an increase in carbon dioxide production means an increase in the rate of cellular respiration. If the amount of substrate, sucrose, is increased then the rate of cellular respiration and carbon dioxide production will also increase. This is because an increase in the availability of the substrate...
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