There are two types of cellular respiration: Aerobic and Anaerobic. Cellular respiration is a fundamental process for the production of ATP.
Different types of cellular respiration exist because living organisms have evolved various mechanisms to meet their energy needs and adapt to different environmental conditions.
Moreover, the diversity in respiration types reflects the flexibility and efficiency of biological systems. Usually, the existence of different types of respiration is a testament to the adaptability and diversity of life on Earth.
Besides, organisms have developed various strategies to cope with different environmental conditions and energy requirements, allowing them to thrive in a wide range of ecosystems.
What is Respiration?
Respiration refers to the biological process by which living organisms, particularly animals and plants, obtain energy from their surroundings and use it to sustain life.
In simpler terms, it is the process of breathing and utilizing oxygen to convert food (usually glucose) into energy, releasing carbon dioxide as a byproduct.
Types of Respiration
Generally, there are three types of Respiration:
- External Respiration
- Internal Respiration
- Cellular Respiration
However, the terms “external respiration,” “internal respiration,” and “cellular respiration” typically refer to different aspects of the respiratory and metabolic processes in organisms.
In this article, we will give complete details of types of cellular respiration.
What is Cellular Respiration?
Usually, Cellular respiration is a set of metabolic processes that occur within cells to convert biochemical energy derived from nutrients into adenosine triphosphate (ATP), the energy currency of cells.
This process occurs in three main stages:
- the Krebs cycle (or citric acid cycle), and
- the electron transport chain.
Cellular respiration is a crucial part of the energy-producing mechanisms in living organisms, allowing them to harness energy stored in food and use it for various cellular activities.
Types Of Cellular Respiration
Usually, there are two main types of cellular respiration:
- Aerobic Respiration
- Anaerobic Respiration
1. Aerobic Respiration (With Oxygen)
Aerobic respiration is a biological process that takes place in the presence of oxygen. Usually, it is the most efficient way for many organisms, including humans, to generate energy from the food they consume.
Equation Of Aerobic Respiration
The overall equation for aerobic respiration, which summarizes the chemical processes involved, can be expressed as follows:
C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + Energy (as ATP)
(glucose) + (oxygen) ⇒ (carbon dioxide) + (water) + Energy
In this equation:
- C6H12O6 represents glucose, a sugar molecule that is the primary energy source.
- 6 O2 represents oxygen, which is required for the process to be aerobic.
- 6 CO2 represents carbon dioxide, a waste product expelled from the body during exhalation.
- 6 H2O represents water, another waste product.
- “Energy” refers to the production of adenosine triphosphate (ATP), the cells’ primary energy currency.
The process begins in the cell’s cytoplasm with a series of chemical reactions known as glycolysis.
During glycolysis, a molecule of glucose (a type of sugar) is broken down into two molecules of pyruvate, releasing a small amount of ATP (adenosine triphosphate) and NADH (nicotinamide adenine dinucleotide).
Citric Acid Cycle (Krebs Cycle):
The pyruvate molecules produced in glycolysis enter the mitochondria, the cell’s energy-producing organelles.
In the mitochondria, the pyruvate is further broken down in a series of reactions called the citric acid cycle or Krebs cycle. This cycle generates more ATP and high-energy electron carriers (NADH and FADH2).
Electron Transport Chain:
The high-energy electron carriers (NADH and FADH2) generated in the previous steps donate their electrons to an electron transport chain in the inner mitochondrial membrane.
As electrons move along the chain, they release energy, which is used to pump protons (hydrogen ions) across the inner mitochondrial membrane.
The accumulation of protons on one side of the inner mitochondrial membrane creates a proton gradient. This gradient creates a flow of protons back through an ATP synthase enzyme, which uses the energy from this flow to generate a large amount of ATP.
Generally, the end products of aerobic respiration are carbon dioxide (CO2) and water (H2O), both of which are released as waste products.
The net result is the production of a substantial amount of ATP, which serves as the primary energy currency for the cell and is used to power various cellular processes and activities.
Aerobic respiration is highly efficient because it can yield a large amount of ATP compared to anaerobic respiration.
This makes it the preferred energy production pathway for many complex organisms, as it allows them to sustain their metabolic functions and overall survival.
2. Anaerobic Respiration (Without Oxygen)
Anaerobic respiration is a biological process that occurs in the absence of oxygen. It is a less efficient way for cells to generate energy than aerobic respiration but can be useful when oxygen is limited or unavailable.
Equation Of Anaerobic Respiration
The chemical equation for anaerobic respiration, specifically lactic acid fermentation, is as follows:
C6H12O6 -> 2 C3H6O3 + Energy (in the form of ATP)
(glucose) ⇒ (lactic acid) + (Energy)
In this equation:
- C6H12O6 represents glucose, the initial sugar substrate.
- C3H6O3 represents two molecules of lactic acid.
- Besides, “Energy” signifies adenosine triphosphate (ATP) production, the cell’s primary energy currency.
- This equation represents lactic acid fermentation, an anaerobic respiration in certain cells when oxygen is limited.
- Instead of fully breaking down glucose into carbon dioxide and water, as in aerobic respiration, lactic acid fermentation converts glucose into lactic acid, providing a limited amount of energy in the form of ATP. This pathway is less efficient than aerobic respiration but allows cells to continue functioning without oxygen.
Working Of Anaerobic Respiration
- Glycolysis: Anaerobic respiration, like aerobic respiration, begins with glycolysis, a series of chemical reactions that break down a molecule of glucose into two molecules of pyruvate. Further glycolysis occurs in the cell’s cytoplasm, yielding a small amount of ATP and NADH.
- Fermentation: In the absence of oxygen, the pyruvate molecules produced in glycolysis cannot enter the citric acid (Krebs) cycle as they do in aerobic respiration. Instead, they undergo a process called fermentation. Further, fermentation can take different forms depending on the organism and its metabolic pathways:
Types Of Anaerobic Respiration
Usually, anaerobic respiration encompasses several types, the most common forms of lactic acid fermentation and alcoholic fermentation. These types of anaerobic respiration differ in their end products and the organisms that perform them:
- Alcoholic fermentation
- Lactic acid fermentation
- Other Variation
Lactic acid fermentation
Lactic acid fermentation is a metabolic process in certain microorganisms, including bacteria and muscle cells when oxygen is scarce or unavailable.
This anaerobic fermentation pathway allows cells to produce energy and regenerate NAD+ to sustain glycolysis. Here’s how lactic acid fermentation works:
Usually, the process begins with glycolysis, which occurs in the cell’s cytoplasm. During glycolysis, one glucose molecule is broken down into two pyruvate molecules, producing a small amount of ATP and NADH.
Without oxygen or when oxygen levels are low, the cell cannot proceed with aerobic respiration. To keep glycolysis going, the cell needs a way to regenerate NAD+ to continue to accept electrons during glycolysis.
Chemical Equation of Lactic Acid Production:
In lactic acid fermentation, the surplus NADH from glycolysis donates its electrons to pyruvate, which converts it into lactic acid. This process regenerates NAD+ and allows glycolysis to continue, albeit at a reduced rate.
The overall chemical equation for lactic acid fermentation is as follows:
Glucose + 2ADP +2NAD+ → Pyruvic acid + 2 ATP +2NADH; Pyruvic acid + 2NADH → Lactic acids + 2 NAD+.
Lactic acid, a weak organic acid, can accumulate in cells and cause muscle fatigue, soreness, and cramping in humans when produced in muscle cells during intense physical activity.
In microorganisms, such as certain bacteria, lactic acid fermentation is used to preserve food products like yoghurt, sauerkraut, and pickles. It also plays a role in the production of some types of cheese.
Lactic acid fermentation is just one of several fermentation processes used by living organisms. This process generates energy in the absence of oxygen.
Other common types of fermentation include alcoholic fermentation, where ethanol is produced, and acetic acid fermentation, which produces acetic acid.
Usually, alcoholic fermentation is also known as alcoholic respiration. It is an anaerobic metabolic process in which certain microorganisms, such as yeast and some types of bacteria, convert sugars into ethanol (alcohol) and carbon dioxide.
This fermentation process has a variety of practical applications, most notably in producing alcoholic beverages like beer and wine.
Working of Alcoholic Fermentation:
The process begins with glycolysis, which occurs in the cell’s cytoplasm. During glycolysis, one glucose molecule is broken down into two pyruvate molecules. These generate a small amount of ATP and NADH.
Alcoholic fermentation is initiated when oxygen is scarce or absent, preventing the cell from proceeding with aerobic respiration. Without oxygen, cells need an alternative way to regenerate NAD+ to keep glycolysis going.
During alcoholic fermentation, the surplus NADH produced in glycolysis donates its electrons to pyruvate, converting it into ethanol (alcohol) and carbon dioxide.
This process regenerates NAD+ and allows glycolysis to continue at a reduced rate. The overall chemical equation for alcoholic fermentation is as follows:
Pyruvate + NADH → Ethanol + NAD+ + Carbon Dioxide
Alcoholic fermentation is widely used to produce alcoholic beverages, as yeast cells convert the sugars in grape juice, malted barley, or other sources into ethanol and carbon dioxide, producing the desired alcoholic content.
Additionally, it has industrial applications in producing biofuels, such as ethanol, for fuel in some parts of the world. This process is also essential in the leavening of bread. Here, yeast produces carbon dioxide gas, causing the dough to rise.
Alcoholic fermentation is one of several types of cellular respiration processes used by living organisms to generate energy in the absence of oxygen.
Other common types of fermentation include lactic acid fermentation, which produces lactic acid, and acetic acid fermentation, which produces acetic acid.
In addition to lactic acid and alcoholic fermentation, some microorganisms may perform other forms of anaerobic respiration, such as mixed acid fermentation and propionic acid fermentation.
These variations can yield different end products and play roles in various biological and industrial processes. The type of anaerobic respiration a cell or organism uses depends on its metabolic pathways and the specific conditions it encounters.
Each type of anaerobic respiration allows cells to continue producing some energy without oxygen. Still, they result in different waste products, affecting the cell and its environment.
Difference Between Types Of Cellular Respiration
|Requires oxygen for the process
|Occurs in the absence of oxygen
|Highly efficient, yielding more ATP
|Less efficient, yielding less ATP
|Produces carbon dioxide (CO2) and water (H2O) as waste products
|Produces lactic acid (in animals) or alcohol (in some microorganisms) as waste products
|Generates a significant amount of ATP
|Yields a smaller amount of ATP
|Common in complex organisms like humans
|Found in some microorganisms and in specific conditions in complex organisms
|It involves glycolysis, the citric acid cycle (Krebs cycle), and the electron transport chain
|It begins with glycolysis and proceeds to fermentation
|Humans and most animals typically perform aerobic respiration
|Yeast and some bacteria undergo alcoholic fermentation, while animals may perform lactic acid fermentation during intense exercise
|Energy Output per Glucose Molecule
|Produces 36-38 ATP (net gain) per glucose molecule
|Produces only 2 ATP (net gain) per glucose molecule in lactic acid fermentation; 2 ATP in alcoholic fermentation
Remember that the specific type of anaerobic respiration may vary depending on the organism and conditions. Lactic acid and alcoholic fermentation are two common forms of anaerobic respiration. However, there can be other variations in some microorganisms.
Cellular respiration is a fundamental process for producing ATP, which is used to power various cellular activities, including muscle contraction, active transport, and the synthesis of macromolecules.
It is a key aspect of life, allowing organisms to extract energy from their environment and maintain the energy balance necessary for survival and growth.
Usually, Aerobic respiration types of cellular respiration allow cells to generate ATP without oxygen, but it is less efficient than aerobic respiration.
The by-products of anaerobic respiration, such as lactic acid or ethanol, can accumulate and may have physiological or industrial significance.
Aerobic respiration is the most efficient type of cellular respiration, and it requires the presence of oxygen. It takes place in the mitochondria of eukaryotic cells.