BL1410 Respiration Lab Protocol and questions .pdf - BL1410...

BL1410 Principles of Biology, Michigan Technological University
Laboratory Protocol
1
Name: ______________________________
Section (table): _______________________
Respiration and Fermentation
Background
As we learned in lecture and in a previous lab, photosynthesis is the process by which light
energy is used to fix carbon dioxide (CO
2
) into sugar. Organisms that use inorganic sources of
carbon are autotrophs Autotrophs that perform photosynthesis get their energy from light, and
in the process make organic materials such as carbohydrates, are called photoautotrophs .
Heterotrophs are other organisms that are unable to fix inorganic carbon such as CO
2
and thus
get their carbon and their energy (formation of ATP) from breaking the bonds in the organic
matter made by the autotrophs. This process is part of cellular respiration . The overall chemical
equation for complete aerobic respiration is:
6 𝑂𝑂
2
+ 𝐶𝐶
6
𝐻𝐻
12
𝑂𝑂
6
→ 6 𝐶𝐶𝑂𝑂
2
+ 6 𝐻𝐻
2
𝑂𝑂 + ATP
However, if oxygen is not available, some organisms can still make use of the substrates such as
sugars by anaerobic respiration . For example, many organisms can aerobically metabolize
sugars (simple carbohydrates) but if they are in an anaerobic environment they can undergo
fermentation of the sugars (actually the Pyruvates produced by glycolysis). Yeast
( Saccharomyces cerevisiae ) can undergo alcohol fermentation in which they convert pyruvates
into acetaldehyde) and then to ethanol, CO
2
and some energy. The simple equation for this is
shown below:
If the sugar is glucose then
𝐶𝐶
6
𝐻𝐻
12
𝑂𝑂
6
→ 2 𝐶𝐶
2
𝐻𝐻
5
𝑂𝑂𝐻𝐻 + 2 𝐶𝐶𝑂𝑂
2
+ ATP
However, not all sugars are the same with regard to the ability of yeast to metabolize them (break
them down) and use them as an energy source. In addition, the breakdown product (ethanol)
slows the fermentation process as the concentration increases because yeast growth is inhibited
by ethanol concentrations (Stanley et al. 2010)
Objectives
In this lab you will do two exercises to measure aspects of yeast metabolism. In part A you will
examine the pattern of production of CO
2
and assess the consumption of O
2
by yeast when
exposed to different substrates (sugars). For these measurements you will use CO
2
and O
2
sensors to measure the amount of each gas in the headspace of your solutions. In part B you will
measure gas displacement as an indicator of the amount of CO
2
produced when yeast are exposed
to different levels of ethanol and incubated in fermentation tubes.

BL1410 Principles of Biology, Michigan Technological University
Laboratory Protocol
2
Chemicals Used
● Ethanol
● Sucrose
● Fructose
● Glucose (Dextrose)
● Lactose
Safety Precautions for the Laboratory
1. Safety goggles must be worn while pouring and working with chemicals.
2. Ethanol is highly volatile, flammable, and should be kept sealed whenever possible.