CELLULAR RESPIRATION:

AEROBIC VERSUS ANAEROBIC RESPIRATION

MARIA LILIBETH S. FUERTES

MT - I
Have you ever wondered what do organisms such as fishes,
humans, birds, plants, bacteria and fungi have in common?

All of these organisms, whether they are made up of

trillions of cells like humans or made up of a single cell
such as yeast, need to produce energy in order to
survive.
 All forms of animals must consume food to live. This food
is used by the cells to create the energy required to fuel the
body and perform life functions. The process of converting
the food you eat into a source of energy that can be used by
your body is called cell respiration. It is a series of
metabolic pathways which extract the energy from the
bonds in glucose and convert it into a form that all living
things can use—both producers (such as plant and algae)
and consumers (such as heterotrophic bacteria, animals, and
fungi).
 In order for these chemical reactions to happen,
specific types of energy molecules are required. These
molecules were formed by the energy released during
cell respiration in the mitochondrion which is
considered as the “powerhouse of the cell”. The energy
released during cell respiration was packaged by the
cells into a form of chemical energy which is used to fuel
chemical reactions inside your body. This type of energy
molecule which is known as the “energy currency” of the
cell is called adenosine triphosphate (ATP).
 Cellular respiration is an
energy releasing process that
happens in two biochemical
pathways; aerobic and
anaerobic.
Whether it is aerobic or
anaerobic respiration, the first
stage of cellular respiration is a
chemical pathway known as
glycolysis.
Aerobic Respiration begins in the cytoplasm and ends in the mitochondria.
(Image retrieved from: Cyber Ed® Multimedia Courseware - Cellular
Respiration Program Supplement)
AEROBIC RESPIRATION
Aerobic respiration is a set of metabolic reactions
that take place in the presence of oxygen, occurring in
a cell to convert chemical energy into ATPs. During
aerobic respiration, oxygen combines with glucose
and glucose is broken down to create energy. This
complex process begins in the cytoplasm and ends in
the mitochondria. Water and carbon dioxide are
released as waste products. The energy is used to
form 36 molecules of ATP for the cell.
• Aerobic respiration takes place in all plants, animals, birds,
and humans, except for some primitive prokaryotes.
• In aerobic respiration, oxygen acts as an electron
acceptor which helps produce ATPs more effectively and
more quickly.
• The double bond in the oxygen has higher energy than
other bonds which aids to produce more ATPs.
• It is the preferred method of degradation of pyruvate after
glycolysis where the pyruvate then enters the
mitochondria to be fully oxidized during the Krebs cycle.
• The process of aerobic respiration is utilized for the
oxidation of carbohydrates, but products from fats and
proteins are also used as reactants.
• Carbon dioxide gas and water are the two products of
aerobic respiration along with the energy that is used to add a
third phosphate group to ADP and form ATP.
• Other energy-rich molecules like NADH and FADH2 are
converted into ATP via electron transport chain with oxygen
and protons.
• In aerobic respiration, most ATPs are produced during
oxidative phosphorylation where the energy of oxygen
molecule is used to pump protons out of the membrane.
• The passage of protons creates a potential that is then used to
initiate ATP synthase and produce ATP from ADP and a
phosphate group.
• Ideally, a total of 38 ATPs is produced at the end of the aerobic
respiration. However, some energy is lost due to leaking of the
membrane or the cost of moving pyruvate through the cell, as a
result of which about 29-30 ATPs are only produced.
• Aerobic respiration results in complete oxidation of
carbohydrate molecules which take place in the mitochondria
of eukaryotic cells as the enzymes for the process are present
there.
ANAEROBIC RESPIRATION
Anaerobic respiration is a process
of cellular respiration where the high
energy electron acceptor is neither
oxygen nor pyruvate derivatives.
Two important types of anaerobic
respiration are alcoholic fermentation
and lactate fermentation. Both of
these types of respiration employ
glycolysis (that is, glucose is broken
down in both), but both end up with The two types of Anaerobic Respiration. (Image retrieved from: Cyber
Ed® Multimedia Courseware - Cellular Respiration Program
different products. Supplement)
• In anaerobic respiration, the electron acceptor can be sulfate
ion (SO4–) or nitrate ion (NO3–) or a variety of other molecules.
• Some archaea, called methanogens, are known to use
carbon dioxide as the electron acceptor, producing methane as
a by-product.
• Similarly, another group of purple sulfur bacteria use sulfate
as an electron acceptor, thus producing hydrogen sulfide as a
by-product.
• These organisms reside in low-oxygen environments and
thus opt for anaerobic pathways to break down the chemical
fuels.
• Anaerobic respiration is similar to aerobic respiration in that
the molecules enter the electron transport chain to pass the
electrons to the final electron acceptor.
• The final electron acceptors involved in anaerobic respiration
have a smaller reduction potential than oxygen molecules
which results in less energy production.
• Anaerobic respiration, however, is essential for bio-
geochemical cycles of carbon, nitrogen, and sulfur.
• The nitrate that acts as an electron acceptor in anaerobic
respiration produces nitrogen gas as a by-product, and this
process is the only route for fixed nitrogen to reach the
atmosphere.
• Fermentation is another pathway for anaerobic respiration,
where the only energy extraction pathway is glycolysis, and
the pyruvate is not further oxidized via the citric acid cycle.
• The energy-rich molecule, NADH, is also not utilized during
fermentation.
• Anaerobic respiration takes place in many environments like
freshwater, soil, deep-sea surfaces. Some microbes in
oxygenated environments also utilize anaerobic respiration
because oxygen cannot readily diffuse through their
surface.
• Anaerobic respiration and fermentation, both take place in the
cytoplasm of the prokaryotic cell.
Anaerobic respiration and fermentation processes take
place in the muscle cells during immediate contraction
and relaxation.
• Fermentation results in a total gain of only two ATPs per
glucose molecule.
Summary of Aerobic and Anaerobic Respiration. (Image retrieved from: Cyber Ed® Multimedia Courseware - Cellular
Respiration Program Supplement)
KEY DIFFERENCES BETWEEN AEROBIC AND ANAEROBIC RESPIRATION
Basis for comparison Aerobic respiration Anaerobic respiration
Definition Aerobic respiration is a set of metabolic reactions
Anaerobic respiration is a process of cellular
that take place in the presence of oxygen,
respiration where the high energy electron acceptor
occurring in a cell to convert chemical energy into
is neither oxygen nor pyruvate derivatives.
ATPs.
Overall equation The overall equation of aerobic respiration is: The overall equation of anaerobic respiration is:
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy C6H12O6 → C2H5OH + CO2 + energy
Presence of Aerobic respiration takes place in the presence of Anaerobic respiration takes place in a condition
oxygen oxygen. where there is a low oxygen environment

Exchange of There is an exchange of gases during aerobic

The exchange of gases doesn’t take place during
gases respiration where oxygen is absorbed, and carbon
anaerobic respiration. However, some gases like
sulfur and nitrogen gases are released by some
dioxide is released.
organisms
Location Aerobic respiration, after glycolysis, occurs in the
Anaerobic respiration occurs only in the cytoplasm
mitochondria of
of a cell.
eukaryotes and cytoplasm of prokaryotes.
End Products The end products of aerobic respiration are carbon The end products of anaerobic respiration are acids,
dioxide, water, and energy. alcohols, gases, and energy
Energy A total of 38 ATPs are produced during aerobic
Only 2 ATPs are formed during anaerobic
Produced respiration, some of which are lost during the
respiration.
process.
KEY DIFFERENCES BETWEEN AEROBIC AND ANAEROBIC RESPIRATION

Basis for comparison Aerobic respiration Anaerobic respiration

Reactants Some other electron acceptors like
Carbohydrates and oxygen are the
sulfur and nitrogen are required
prerequisites of aerobic respiration.
along with the carbohydrates.
Oxidation Incomplete oxidation of carbohydrates
Complete oxidation of carbohydrates
takes place during anaerobic
takes place during aerobic respiration.
respiration.
Nature of the Aerobic respiration is comparatively Anaerobic respiration is shorter than
process longer than anaerobic respiration. aerobic respiration.
Occurs in Anaerobic respiration occurs in
Aerobic respiration occurs in most of primitive prokaryotes. Anaerobic
the higher organisms like plants and respiration also takes place in the
animals. muscle cells in humans during
extreme movements
ACTIVITY
Directions: Identify the term being described by filling in the
blanks.
1. The process of converting the food you eat into a source of energy
that can be used by your body is called __ __ __ __ __ __ __ __ __ .
2. The molecule used by cells to store and transfer energy is __ __ __.
3. Aerobic respiration begins in the __ __ __ __ __ __ __ __ __ and
ends in the mitochondria.
4. __ __ __ __ __ __ __ happens when oxygen is present and includes
glycolysis, Krebs cycle, and Electron transport.
5. In aerobic respiration, oxygen acts as an electron __ __ __ __ __ __
which helps produce ATPs more effectively and more quickly.
6. Carbon dioxide gas and __ __ __ __ __ are the two products
of aerobic respiration.
7. __ __ __ __ __ __ are known to use carbon dioxide as the
electron acceptor, producing methane as a by-product.
8. Anaerobic respiration and fermentation, both take place in
the cytoplasm of the __ __ __ __ __ __ cell.
9. Cell organelle which acts as the cell’s power plant to burn
glucose and store energy as ATP is the __ __ __ __ __ __ __
10.Anaerobic respiration and fermentation processes take
place in the __ __ __ __ __ __ cells during immediate
contraction and relaxation.
Links/ References:

Interactive Biology Multimedia Courseware, Copyright 1998 CyberEd, Inc.

https://byjus.com/biology/aerobic-anaerobic-respiration/#aerobic
https://microbenotes.com/aerobic-vs-anaerobic-respiration/