Respiration

Respiration is the process in which organisms exchange gases between their body cells and the environment. From plants and animals to prokaryotic bacteria, archaeans, eukaryotic protists, fungi, and animals, all living organisms undergo respiration. During normal human respiration, glucose reacts with oxygen to produce the energy needed for growth, repair and movement. Water and carbon dioxide are bi-products of respiration that need to be excreted.

Respiration could be defined as a metabolic biochemical process that takes place in all living cells of an organism where they produce energy by intake of oxygen and liberation of carbon dioxide from the oxidation of various organic substances. The energy produced is in the form of Adenosine-triphosphate or ATP which is also known as the energy molecule.

The different types of respiration:

Two types of respiration processes have been observed

1. Aerobic respiration 

2. Anaerobic respiration

Aerobic respiration 

It is a type of cellular respiration that takes place in the presence of oxygen and produces energy. It is observed in both plants and animals and the end product of this type of respiration is water and Carbon dioxide (CO2).

Have a look at the reaction which takes place during aerobic respiration.

Glucose (C6H12O6)  + Oxygen 6(O2) → Carbon-dioxide 6(CO2)  +  Water 6(H2O) + Energy (ATP)

As observed, in this type of respiration, Glucose molecules are split in the presence of oxygen and the end or by-products which are released are (CO2), water and energy in the form of ATP. The total energy released in this reaction is 2900 KJ which is used to produce ATP molecules. It is observed in all types of multicellular organisms. 

Aerobic Respiration in Plants:

In plants, aerobic respiration starts when oxygen or O2 enters plant cells through the stomata found in the epidermis of leaves. Then the process of photosynthesis is carried out which produces food for the plant body and releases energy. The chemical reaction that takes place is below:

Carbon dioxide 6(CO2)  + Water 6(H2O) → Glucose  (C6H12O6)   +  Oxygen 6(O2)  

Anaerobic Respiration

is another type of cellular respiration that takes place in the absence of oxygen and produces energy. In this process,  glucose breaks down without the help of oxygen and the by-products produced are alcohol, (CO2) and energy or ATP. The process takes place in the cytoplasm of a cell. The chemical reaction of this process is as follows:

Glucose (C6H12O6) → Alcohol 2(C2H5OH) + Carbon dioxide 2(CO2) + Energy (ATP )

Aerobic Respiration could be divided into 

1. Lactic Acid Fermentation

2. Alcoholic Fermentation

Lactic Acid Fermentation: It is the type of anaerobic fermentation where glucose is split in the absence of oxygen to produce two molecules of lactic acid and two molecules of ATP.

Respiration may refer to y of the three elements of the process. First, respiration may refer to external respiration or the process of gas exchange between the air and an organism's cells. Secondly, respiration may refer to internal respiration, which involves a gas exchange between the blood and body cells. Aerobic respiration is cellular respiration that requires oxygen while anaerobic respiration does not.

External Respiration

External respiration or breathing is one of the methods for obtaining oxygen from the environment. In animal organisms, the process of external respiration is performed in several different ways. Animals that lack specialized organs for respiration rely on diffusion across external tissue surfaces to obtain oxygen whereas others either have organs specialized for gas exchange or have a complete respiratory system. In organisms such as nematodes (roundworms), gases and nutrients are exchanged with the external environment by diffusion across the surface of the animal's body. Insects and spiders have respiratory organs called tracheae, while fish have gills as sites for gas exchange.

Internal Respiration

Internal respiratory processes explain how oxygen gets to body cells. Internal respiration involves the transportation of gases between the blood and body tissues. Oxygen within the lungs diffuses across the thin epithelium of lung alveoli (air sacs) into surrounding capillaries containing oxygen-depleted blood. At the same time, carbon dioxide diffuses in the opposite direction (from the blood to lung alveoli) and is expelled. Oxygen-rich blood is transported by the circulatory system from lung capillaries to body cells and tissues.

Cellular Respiration

The oxygen obtained from internal respiration is used by cells in cellular respiration. To access the energy stored in the foods we eat, biological molecules composing foods (carbohydrates, proteins, etc,) must be broken down into forms that the body can utilize. This is accomplished through the digestive process where food is broken down and nutrients are absorbed into the blood. As blood is circulated throughout the body, nutrients are transported to body cells. 

The Chemical Reaction is :

(GLUCOSE) C6H12O6 + 2 ADP + 2 PHOSPHATE → 2 LACTIC ACID + 2 ATP

During exercise, body muscles use O2 to produce ATP faster than they can be supplied.  When this happens, muscle cells carry out glycolysis faster than they can provide oxygen to the electron transport chain. This is why lactic acid fermentation takes place in our cells after a long session of exercise which makes our muscles sore.

Alcoholic fermentation: In this type of anaerobic respiration, glucose is split in the absence of oxygen two molecules of ethyl alcohol or ethanol, two molecules of Carbon dioxide and two molecules of ATP. The chemical reaction is:

Glucose C6H12O6 → Alcohol 2(C2H5OH) + Carbon dioxide 2(CO2) + Energy (ATP )

Anaerobic respiration could be observed in human muscle cells, bacteria, methanogens and other prokaryotes.

Respiration refers to a person’s breathing and the movement of air into and out of the lungs. Respiration is assessed for quality, rhythm, and rate.

• The quality of a person’s breathing is normally relaxed and silent. Healthcare providers assess the use of accessory muscles in the neck and chest and indrawing of intercostal spaces (also referred to as intercostal tugging), which can indicate respiratory distress. 

• Respiration normally has a regular rhythm. A regular rhythm means that the frequency of the respiration follows an even tempo with equal intervals between each respiration. If you compare this to music, it involves a constant beat that does not speed up or slow down but stays at the same tempo.

• Respiratory rates vary based on age. The normal resting respiratory rate for adults is 10 – 20 breaths per minute (OER #1). Children younger than one year normally have a respiratory rate of 30 – 60 breaths per minute, but by the age of ten, the normal rate is usually 18 – 30.

The Different Stages of Respiration:

Cellular respiration takes place through a range of metabolic pathways. Glucose is broken down into the water, carbon dioxide and some amount of ATP. More ATP is produced later in a process known as oxidative phosphorylation which is powered by the movement of electrons through the electron transport chain. Below is a summary of the different phases of cellular respiration:

• Glycolysis: In this process, a six-carbon sugar, glucose undergoes various chemical transformations. The end product is pyruvate and a three-carbon organic molecule. Two molecules of ATP and NADH are also generated.

• Pyruvate Oxidation: Each pyruvate enters the mitochondrial matrix, and is converted to a two-carbon molecule that is bound with Coenzyme- A. The whole compound is known as acetyl CoA.  The by-products in this reaction are carbon dioxide and NADH.

• Citric Acid Cycle: The Acetyl CoA combines with a four-carbon molecule which undergoes a series of chemical reactions also known as the Citric Acid cycle or the Krebs cycle.  In the end, the initial four-carbon molecule is regenerated with the addition of FADH2, NADH, carbon dioxide and two molecules of ATP. The Krebs cycle is known as the tricarboxylic acid cycle as well.

• Oxidative Phosphorylation: The FADH2 and NADH generated in the Krebs cycle donate their electrons to oxygen through various electron carriers via the electron transport chain in a process known as oxidative phosphorylation. The reaction takes place in the mitochondrial matrix. As electrons move down the chain, there's a release of energy that is used to pump protons out of the matrix and it forms a gradient. The protons then again flow back in the matrix with the help of the enzyme ATP synthase which produces ATP. At the end of the chain, oxygen accepts the electrons and protons to form water.

In the end, 38 molecules of ATP are generated from one molecule of glucose. It should be mentioned that glycolysis can also take place in the absence of oxygen and the process is known as fermentation.

Anaerobic Respiration in Muscles

We all normally obtain energy by aerobic respiration. But when we need extra energy, anaerobic respiration can take place in our muscles for a short time. When we do heavy physical exercise, our muscles need more oxygen. But the supply of oxygen through blood is limited and hence insufficient.

During heavy exercise, some of our muscles respire anaerobically. The anaerobic respiration by muscles brings about the partial breakdown of glucose to form lactic acid. This lactic acid accumulates in the muscles. The accumulation of lactic acid in the muscles causes muscle cramps.

The Significance of Respiration:

Respiration is the energy supplying and releasing process in all living organisms by converting food energy into metabolically usable forms of chemical energy. The process releases energy in a controlled step-by-step manner so it could be properly used for all cellular activities such as metabolism and cell division. Various intermediate products of glycolysis and the citric acid cycle are used in the synthesis of many organic compounds which are used in cellular metabolism. In a plant, the carbon dioxide required for photosynthesis is replenished by the carbon dioxide released in respiration and the oxygen needed for respiration is replenished with the oxygen released in photosynthesis. Therefore respiration and photosynthesis are complementary to each other and maintain the balance of carbon dioxide and oxygen in nature. Respiration also conserves energy. One glucose molecule releases 673Kcal of the energy of which 456 Kcal is conserved in 38 molecules of ATP.