Lynsey Knapp
Mr. Carrico
Biology/ Blue three
12 November, 2009
Respiration and Fermentation
Respiration and Fermentation are two major processes that cells go through. These are
important for the cell to keep it alive and functioning properly. Basically, without these two
things, no living things would exist because cells are the basic units of life. Respiration is the
process that lets go of food energy when oxygen is present (Levine 251). When a cell does
respiration, it requires oxygen and glucose and it gives off carbon dioxide, water and energy.
Basically this process oxidizes food pieces (glucose) into carbon dioxide and water. The energy
released is turned into ATP which is used for activities in the cell.
Cellular respiration catches energy from food in three main stages: glycolysis, the Krebs
cycle, and The electron transport chain. In the first stage, the food particles (glucose in this case)
enter glycolysis, which is a chemical pathway. This stage only captures a small amount of energy
used for making ATP (Levine 252). During glycolysis glucose is turned into pyruvic acid, and
energy is released as the bonds change (Levine 254). Glycolysis can be done both with and
without oxygen, but without oxygen, it is the first stage of fermentation (Bailey par. 1). This
process is so fast, that it can make thousands of ATP molecules in a matter of milliseconds
(Levine 255).
In the second stage, pyruvic acid goes into cellular respirations second stage, which is
known as the Krebs cycle, or the citric acid cycle. The Krebs cycle breaks down pyruvic acid
into carbon dioxide after going through many energy-extracting reactions. It is also called the
citric acid cycle because the first compound formed in the reactions is citric acid (Levine 256).
This stage generates a little more energy than glycolysis.
The final stage of respiration is the electron transport chain. Electron carriers in the
mitochondria of Eukaryotic cells are passed to oxygen, creating ATP (Bailey par. 3). This needs
reactants from the other stages in respiration. The electron transport chain uses electrons from
the previous stages to change ADP into ATP (Levine 258). Most of the energy in the respiration
process comes from this stage (Levine 252).This does directly require oxygen, unlike the other
two stages (Bailey par. 4). The oxygen is essential for disposing the disposing of low energy
electrons and hydrogen ions, which are the waste products of respiration (Levine 258). In all,
cellular respiration produces and releases 36 molecules of ATP for every molecule of glucose
(Levine 260).
Without respiration photosynthesis couldn’t happen. In fact, they are the exact opposite.
When plants have energy, water, and carbon dioxide they let out oxygen and glucose, which is
photosynthesis. Then they take that oxygen and glucose, and produce carbon dioxide, water, and
energy in the respiration process. This creates a cycle which keeps plants alive. Photosynthesis
put energy into a plant, and respiration takes it back out, like breathing. Photosynthesis is
removing carbon dioxide from the atmosphere, while respiration puts it back, and photosynthesis
releases oxygen, and respiration takes it in. Respiration takes place in almost all life, but
photosynthesis occurs only in plants, algae, and a few bacteria (Levine 253).
If no oxygen is present some cells are still able to produce ATP through glycolysis
(fermentation par. 1). This is referred to as fermentation, sometimes it is put together with
glycolysis and called anaerobic respiration. Fermentation is the process in which electron and
hydrogen ions from the NADH made by glycolysis are given to another organic molecule
(Levine 262). During this process NADH is made into NAD+ by turning high energy electrons
back into pyruvic acid, allowing glycolysis to make a supply of ATP. NAD+ is needed for
glycolysis and it requires much less energy for the cell to take NADH and convert it into NAD+,
than it does to just send the NADH to the mitochondria as normal. There are two different forms
of fermentation: alcoholic, and lactic acid fermentation (Levine 262).
Alcoholic fermentation is used to produce alcoholic drinks. Yeast cells produce ethyl
alcohol and carbon dioxide, making alcohol that people drink, and causes bread to rise
(fermentation par. 3). This requires pyruvic acid and NADH, and produces alcohol, carbon
dioxide, and NAD+. When bread rises, the yeast cells are running out of oxygen, and the dough
starts fermenting, giving off bubbles of carbon dioxide, which you see when bread is sliced, the
alcohol produced in this process burns off while baking (Levine 263).
Lactic Acid fermentation happens to most organisms. This converts pyruvic acid into
lactic acid. Lactic acid fermentation doesn’t give off carbon dioxide like alcoholic fermentation
does, but it does restore NAD+ so that glycolysis can keep going like alcoholic fermentation.
This process requires pyruvic acid and NADH then lets out lactic acid and NAD+. Prokaryotes
are used to produce many types of food (including cheese, yogurt, and sour cream). Lactic acid
fermentation is also used to produce pickles and sauerkraut. (Levine 263)
Humans do lactic acid fermenting. Some muscles are not capable of holding oxygen for
very long, so when people exercise, this causes the muscle to use lactic acid fermentation, so that
it can produce more ATP and keep functioning (fermentation par. 4). This supplies a large
amount of ATP when there are quick energy bursts (Levine 263). During quick spurts of activity,
the body can use ATP already stored in the muscles and Lactic acid fermentation. When doing
longer activities, cellular respiration has to be used. In the beginning of working out, the body
uses all three of its ATP sources (Levine 265). Then, it has to resort to using fermentation for a
quick boost. Muscles hurt after a heavy work out because the lactic acid builds up in them,
causing discomfort. Without fermentation, exercising would be impossible, and cells would die
quicker because they would not have any back-up options. Respiration and fermentation are two
of the most important processes a cell goes through, so if they are not given enough of the
resources they need to function, dieing is very possible.
Works cited
Bailey, Regina. "Cellular Respiration." About.com:Biology. 16 Nov 2009.
<http://biology.about.com/od/cellularprocesses/a/cellrespiration.htm>. Web.
"Fermentation and Anaerobic Respiration." VBS. 20 feb 2000. Web. 16 Nov 2009.
<http://staff.jccc.net/pdecell/cellresp/fermentation.html>.
Levine, Joseph, and Kenneth Miller. Biology. Boston, Massachusetts: Pearson, 2010. 251 252
253 258 260 262 263 265. Print.