Life Process- 2 Respiration


Every living organism needs energy to perform various life activities, and the process of respiration fulfills this energy requirement. During respiration, this food is broken down in the presence of oxygen, and energy is released during respiration.

Breathing- exchange of gases between the animal body and its external environment, also called ventilation or breathing.

Cellular respiration

Under cellular transport of gases O2 and CO2 between the respiratory surface and the cells. The biochemical process that occurs within cells and oxidizes food to obtain energy, is known as cellular respiration.

In the process of cellular respiration energy released is immediately used to synthesize a molecule called ATP which is used to fuel all other activities in the cell. In these processes, ATP breaks down to produce a fixed amount of energy which drives the endothermic reactions taking place in the cell.

release of energy in cellular respiration

ATP-ATP is termed as the energy currency for most cellular processes. Endothermic processes in the cell use ATP to drive the reactions. When the terminal phosphate linkage in ATP is broken using water, the energy equivalent to 30.5 kJ/mol is released.

Aerobic respiration

In the aerobic type of respiration, oxygen is required. In this form of respiration oxygen is required that releases a much larger quantity of energy in the form of ATP. It occurs in the mitochondria of the eukaryotes and in the folded plasma membrane (mesosome) of the prokaryotes. The release of energy in the process of aerobic respiration is greater than in the anaerobic process.

break down of glucose by various pathways - aerobic respiration

Anaerobic respiration

In Anaerobic respiration, oxygen is not required. In this type of respiration, organic molecules are incompletely broken in the cytosol of the cell and only a small fraction of energy is captured as ATP for use by the cell. Takes place in the cytoplasm.

Incomplete oxidation of organic substrate takes place in lower organisms such as bacteria, and fungi, and in higher animals under limiting conditions of oxygen.

Sometimes, in the lack of oxygen in our muscle cells, another pathway starts for the breakdown of pyruvate to produce energy. In this pathway, the pyruvate gets converted into lactic acid which is also a three-carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes muscle cramps.

lactic acid formation in Muscles

Another process takes place in yeast called fermentation in this process breakdown of glucose into a three-carbon molecule called Pyruvate. It converts into ethanol and carbon dioxide in yeast during fermentation this process takes place in the absence of air (oxygen).

fermentation in yeast - Aerobic respiration

In aquatic animals, respiration takes place by the special organ named Gill, as we know the amount of oxygen dissolved in water is less than in the surrounding. So aquatic animals breathe faster for their need of oxygen. Some lower organisms breathe by means of skin also.

For example- An earthworm does not contain respiratory organs so the entire skin on the body of the earthworm functions as the respiratory surface, frogs show cutaneous respiration during hibernation otherwise frogs are mainly lung-breathing animals

Respiration in Plants

As we know that in plants process of photosynthesis takes place, and in the process of photosynthesis they produce food. In the process of photosynthesis light energy is converted into chemical energy by plants’ photosynthesis and this energy is then stored in the bonds of complex molecules such as glucose, and starch.  The process of respiration is different in plants than in animals.

  • plants exchange gases through stomata, and the large intercellular spaces ensure that all cells are in contact with air Plants. The requirement of O2 is less in plants than in animals and plants have a large surface area (leaves) to absorb the required amount of O2 through diffusion (The direction of diffusion depends on the environmental conditions and the requirements of the plant as in diffusion the movement of particle takes place from higher concentration to lower concentration.)
Respiration through stomata

Respiration through stomata

  • In roots plants also breathe through root nodules.
  • During the daytime the CO2 generated during respiration is used up for photosynthesis, hence there is no CO2 release but they release CO2 during night time.
  • complete combustion of glucose takes place and CO2 and H2O are formed as end products.
  • The utilization of stored food for energy done by the process of respiration. For respiration plants also require O2 and they also give out CO2.
  • The breakdown of complex compounds like fat and protein in simple carbon molecules releases a considerable amount of energy is called respiration. This energy is thus made available to the living cells in the form of ATP (Adenosine Tri-Phosphate).

reaction during respiration

    Respiration in human

    Humans consist a well-developed respiratory system suitable for the higher requirement of oxygen in their bodies. The respiratory system consists of:

    • Nostrils Opening of Nose- Takes part in the Filtration of unwanted particles.
    • Nasal cavity– It is covered with mucous membrane and cilia- It Traps dust, and bacteria; warms and moistens the air in the pharynx.
    • pharynx (Throat) –It is a muscular Tube- the common passage for both respiratory gases and food moving into the digestive passage, separated by the epiglottis
    •  Epiglottis is a flap-like structure that closes the tracheal opening (opening of the windpipe) called glottis when food is swallowed.
    • Larynx (Voice Box) A small cartilaginous organ with vocal cords- Connects the pharynx to the trachea it helps in sound production.
    • Trachea (Windpipe)- Supported by C-shaped cartilaginous rings to prevent it from collapsing. The trachea divides into two bronchi and enters the two lungs
    • alveoli (singular–alveolus) balloon-like structures inside the lungs.
    • Bronchus (Plural: Bronchi) Elastic, ciliated and covered with mucous epithelium Enters the lungs and divides to form secondary bronchi, tertiary bronchioles, and ultimately terminal bronchioles. Together they form the bronchial tree.
    Process of Breathing in Human
    • Inspiration or taking air in A muscular dome-shaped diaphragm is present at the base of the lungs. During inspiration, The lower surface of the lungs is pulled downwards and the volume of the lungs increases during the time while oxygen-containing air is taken in.
    • Expiration or forcing air out In this step relaxation of external intercostal muscles and contraction of internal intercostal muscles The abdominal organs press up against the diaphragm. This change decreases the volume of the chest cavity, thus, increasing the air pressure within the lungs and the air, which is laden with CO2 and is forced out.
    • The process of Inspiration and Expiration is collectively called   pulmonary ventilation
    Respiratory organ in human
    respiratory system in human
    • Air is taken in through the nostrils and filtered inside by the passage having fine hairs. The air passes into the lungs through the throat by the nostrils. The trachea is a ring-like structure that prevents the wind to collapse.
    • The lungs are the main respiratory organs. Lungs are the chief centers of respiration in humans.  Each lung consists of a tree-like system of branched bronchial tubes.
    • The exchange of gases takes place on the surface of the alveoli.
    • when we breathe in, we lift our ribs and flatten our diaphragm, and the chest cavity becomes larger as a result. Because of this, the air is sucked into the lungs and fills the expanded alveoli.
    • During inspiration, the rib cage moves outwards and upwards and increases the volume of the chest cavity, lowering the air pressure within the lungs.
    • O2 from alveoli passes into capillaries and CO2 from other capillaries diffuses into alveoli for being removed.
    Exchange of gases between lungs and bloodstream

    There is more oxygen in the alveolar air and more carbon dioxide in the capillaries. Oxygenation of blood takes place in the lungs. Four molecules of oxygen form a reversible bond with hemoglobin forming the compound oxyhemoglobin. Due to the pressure difference of oxygen and carbon dioxide between the alveoli and blood capillaries, the oxygen diffuses from alveolar air into the blood capillaries.

    When the oxygenated blood reaches the tissue surface there is a high concentration of CO2 in the tissues, oxygen used up, and here the low concentration of O2, As a result, the bonds holding oxygen and hemoglobin in Hb (4O2) becomes unstable and blood releases oxygen and takes up CO2. Oxygenated blood is taken from the lungs to the heart by the pulmonary vein.

    During the breathing cycle, when air is taken in and let out, the lungs always contain a residual volume of air so that there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released as Expiration

    The respiratory pigment is hemoglobin in humans which has a very high affinity for oxygen, this is present in RBC. Carbon dioxide is transported in the dissolved form in our blood as it is more soluble in water than oxygen. The carbon dioxide which is dissolved in blood i.e. deoxygenated blood now comes back into the lung and is released as expiration. The oxygenated i.e oxygen-containing blood goes to the heart by the pulmonary vein and circulates all over.

    The regulation of respiration is under nervous control- by the medulla oblongata and pons the brain.

    Some Important terms related to respiration:

    Tidal volumeIn this Volume of air inhaled and exhaled without any effort (normal breathing). – 500mL

    Vital capacity (VC)Volume of air that can be maximally breathed out after a maximum inspiration. – 3400-4800mL

    Residual volume (RV) Volume of air that cannot be forced out even on forced expiration. This is the air that remains in the lungs.

    Vital capacity may be highly reduced in smokers and people suffering from tuberculosis. Athletes and singers on the other hand have a higher vital capacity.

    Some diseases

    • Harmful air-contaminated particles like smoke, and dust particles if inhaled they cause lung cancer as they destroy hair-like structures called cilia present in the lung.
    • Asthma
    • Tuberculosis
    • Bronchitis

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