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Types of Cellular Respiration
An Introduction Reading
Cellular Respiration- Cells get energy for active transport, building materials,
and other processes through cellular respiration. Cellular respiration is the process by
which glucose is broken down to make energy available for cellular activity.
Two types of cellular respiration- There are two main types of cellular
respiration, aerobic and anaerobic (also known as fermentation). During aerobic cellular
respiration, oxygen combines with glucose. In a series of steps which begin in the
cytoplasm and end in the mitochondria, glucose is broken down. Water and carbon
dioxide are released as waste products. Energy is released as the bonds of glucose are
broken. This energy is used to form 36 molecules of ATP for the cell.
C6H12O6 + 6CO2
6CO2+6H20 +36ATP
Sometimes oxygen is not available to a cell or an organism does not contain the enzymes
necessary for aerobic cellular respiration. In such cases, since the cell still requires
energy, the organism must carry out anaerobic cellular respiration (fermentation).
Fermentation is the process in which glucose is broken down without oxygen. There are
two types of fermentation, which both occur in the cytoplasm.
In one type of fermentation, muscle cells, lacking in oxygen due to strenuous
exercise, break glucose down into a compound called lactic acid. Only 2 molecules of
ATP are formed from the energy released from glucose in this reaction, called lactic acid
fermentation. Lactic acid causes muscles to burn and does not meet the cell’s demand for
energy. The human body works hard to obtain more oxygen (by heavier breathing) so
cells can quickly return to aerobic respiration.
Some bacteria also carry out lactic acid fermentation. The food industry makes
use of lactic acid fermentation in bacteria for the production of yogurt, sour cream, and
buttermilk. These foods get their sour taste from the lactic acid formed by bacteria using
the sugars in milk for anaerobic respiration.
C6H12O6
Lactic Acid + 2 ATP
If you have ever observed bread rise, you have observed a second type of anaerobic
respiration called alcoholic fermentation. Yeast cells in dough break down sugars
forming carbon dioxide bubbles causing the dough to expand. A second end product of
alcoholic fermentation is ethyl alcohol. The beverage industry takes advantage of the
process of alcoholic fermentation to make beer and wine. Yeast cells use sugars in grapes
or grains and form carbon dioxide and ethyl alcohol used for making wine or beer, as
well as 2 ATP molecules (for their own use).
C6H12O6
Ethyl Alcohol + CO2 + 2ATP
Types of Cellular Respiration- Review Questions
Aerobic
Cellular
Respiration
Does it
require
oxygen?
Reactants
Products
Where in the
cell does it
occur?
Amount of
ATP made in
the cell
Lactic Acid
Fermentation
Alcoholic
Fermentation