Phases in respiration - class-X

External respiration is the process of gaseous exchange between the external environment and the blood stream. Antonie Lavoiser, a French Nobleman is considered as father of modern chemistry who along with chemistry also contributed in the fields of biology, finance and economics. He explained combustion and respiration in terms of chemical reactions involving oxygen. He showed that respiration was a slow combustion of organic material using inhaled oxygen. 

Cellular respiration is a continuous process of oxidation of food to produce energy. The energy produced is utilized by human beings to carry out all the life processes such as digestion, excretion, circulation etc. Since these are continuous processes and do not stop, so they require continuous energy. If the energy is produced intermittently it will slow down these processes and affect the individual. 

The rate at which oxygen moves from the alveoli of our lungs into our blood depends on the difference in oxygen concentration between the alveoli and the blood. More is the oxygen absorbed by our lungs, more is it utilized by body muscles.

Alveoli are tiny sacs from the bronchiolar extensions within our lungs that allow oxygen and carbon dioxide to move between the lungs and bloodstream. 

So, the correct answer is 'Breathing', 'Cellular respiration' and 'Pulmonary ventilation'.

In humans respiratory system consists of respiratory tract (conducting zone) and lungs (exchange zone). The respiratory tract is the passage from external nostrils to lungs or a passage by which air enters into lungs. The respiratory passage starting from external nostrils is nasal chamber --> internal nares --> nasopharynx -->pharynx --> glottis --> larynx --> trachea --> bronchial tree (bronchi and bronchioles) --> alveoli.

Normal body temperature is around $37^0$C. Fever happens when the body's temperature is higher than normal because of an infection. Fever causes an increase in the heart rate, breathing rate and blood circulation to the skin. This is how the body tries to reduce the heat caused by fever. 

In breathing or cellular respiration, a set of metabolic reactions and processes take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy. Respiration is one of the key ways a cell gains useful energy to fuel cellular activity. Cellular respiration is considered an exothermic redox reaction which releases heat. The overall reaction occurs in a series of biochemical steps, most of which are redox reactions themselves.

During the third trimester, as the uterus continues to grow, it puts pressure on the internal organs and the diaphragm, which in turns restricts the amount of room available for lungs and leads to shortness of breath. So breathing by ribs is more pronounced during pregnancy, as it slightly raises the rib cage and temporarily gives more breathing space to lungs making breathing little easier.

Cutaneous respiration or cutaneous gas exchange, is a form of respiration in which gas exchange occurs across the skin or outer integument of an organism rather than gills or lungs. Cutaneous respiration may be the sole method of gas exchange, or may accompany other forms, such as ventilation. Cutaneous respiration occurs in a wide variety of organisms, including insects, amphibians, fish, sea snakes, turtles, and to a lesser extent in mammals, including humans. 

Gas exchange and respiration are essential if cells are to stay active, grow and divide. All the structures for gas exchange have common as follows:

• They have a large surface area relative to the volume of the organism. 
  
• They are thin and so have a short diffusion pathway. 
  
• They have a moist surface where gases can dissolve first before they diffuse in or out. 
  
• They are able to maintain the diffusion gradient down which the gases can diffuse.
  

Respiration can be cellular and physiological. Cellular respiration takes place in individual cells while physiological respiration is a bulk process. Cellular respiration takes place through a set of metabolic reactions and in the cells which converts biochemical energy from the nutrients into ATP and releases wastes. These reactions are catabolic reactions that releases energy and heat in the process.

The end product of glycolysis is pyruvic acid. The next step is the formation of acetyl coenzyme A (acetyl CoA). Acetyl CoA is the initiator of the citric acid cycle. In carbohydrate metabolism, acetyl CoA is the link between glycolysis and the citric acid cycle. The initiating step of the citric acid cycle occurs when a four-carbon compound (oxaloacetic acid) condenses with acetyl CoA (2 carbons) to form a citric acid (6 carbons).

• Relaxation of the diaphragm and the inter-costal muscles returns the diaphragm and sternum and ribs move into their normal positions and reduce the thoracic volume and thereby the pulmonary volume. 
  
• This leads to an increase in intra-pulmonary pressure to slightly above the atmospheric pressure causing the expulsion of air from the lungs, i.e., expiration. Hence, ribs move out in during exhalation.

Pinnaglobin is a brown-colored respiratory pigment found in the blood of certain mollusks (specifically Pinna).

The respiratory membrane (alveolar-capillary membrane) consists of the alveolar epithelial wall, the capillary endothelial wall, and the fused basement membrane (interstitial space) between them.

Breathing is an act of ventilating a respiratory surface with air. Breathing is usually accomplished through muscular movements that can be divided into inspiration (intake of air ) and expiration (outflow of air). The composition of inhaled air is 20.94 % oxygen, 0.04 % carbon dioxide, 79.02 % nitrogen and trace gases. The composition of exhaled air is 16.49 % oxygen, 4.49 % carbon dioxide, 79.02 % nitrogen and other trace gases. The nitrogen is an inert gas, during breathing, there is no change in nitrogen percentage in inhaled as compared to exhaled air.

During inhalation, diaphragm contraction occurs which induces the lower ribs to move upward and forward, which also increases thoracic volume. The ribs move outward because the central tendon of the diaphragm (at the crown of the dome) pushes down onto the liver and stomach, which act like a fulcrum. Oxygen enters into the alveoli. Alveoli, is the site for gaseous exchange and they increase the surface area for facilitating the process. 
Carbon monoxide has 210 times greater affinity for haemoglobin than oxygen. Thus, the correct answer is option D.

Breathing is the process of moving air into and out of the lungs to facilitate gas exchange with the internal environment, by bringing in oxygen & expelling out carbon dioxide.

Inspiratory reserve volume (IRV) + tidal volume (TV) + expiratory reserve volume (ERV) represents vital capacity (VC). Now, inspiratory capacity is the total volume of air that can be inhaled after a normal expiration. It includes tidal volume and inspiratory reserve volume i.e., IC = TV + IRV. Thus, option (a) is correct which says that vital capacity/.e., IRV + TV + ERV = IC + ERV.

Diaphragmatic or abdominal breathing is the normal pattern of breathing at rest: the abdomen protrudes as the diaphragm is lowered. It is done by contracting the diaphragm, a muscle located horizontally between the chest cavity and stomach cavity. Air enters the lungs and the belly expands during this type of breathing.This deep breathing is marked by expansion of the abdomen rather than the chest when breathing.

The normal respiration rate in an adult rabbit is 30 - 60/minute, but some breathe faster than this if they are hot or stressed.

In fermentation, the carbohydrate gets broken down, but instead of making pyruvate, the final product is a different molecule depending on the type of fermentation. Fermentation is most often triggered by a lack of sufficient amounts of oxygen to continue running the aerobic respiration chain. Humans undergo lactic acid fermentation. Instead of pyruvate, lactic acid is created instead. Other organisms can undergo alcoholic fermentation where the end product is neither pyruvate nor lactic acid. The organism makes ethyl alcohol as an end product. 

The respiratory surface needs moisture for maximum efficiency. Oxygen from the air dissolves in the water on the surface momentarily and this allows the oxygen more time to cross the alveolar membrane. If the surface dries out, gas exchange will happen at a very reduced rate since fast-moving gaseous oxygen molecules do not efficiently cross the alveolar membrane. The reduced gas exchange is mostly likely not enough to support blood oxygenation for vital functions. 

Diffusion is insufficient to meet the oxygen requirement of multicellular organisms like human because all the cells are not direct contact in environment and diffusion is a slow process. Diffusion is too slow to cover the distance between the gas exchange surface and the sites where the oxygen is required. That is why we need a gas transport system - the bloodstream. It would be difficult to allow passive diffusion to transfer oxygen because there would need to be gradients across each and every cell. In the end, it would be too slow and impractical for any multicellular organism to use.

• Trachea consists of C-shaped cartilaginous rings that support the walls of the trachea and prevent its collapse during inspiration. 
• Respiratory centre is located in the medulla oblongata. 
• Yeast undergoes anaerobic respiration to produce ethanol and $CO _{2}$. 
• The type of respiration in insects and fish is tracheal respiration and branchial respiration respectively. 
• ATP is a biologically useful energy produced during respiration. 
• The partial pressure of $O _{2}$ in alveolar air is approximately 104 mm Hg. 
• Vocal cords are present inside the larynx.
  

NAD+ and FAD are co-enzymes required for the completion of many biochemical pathways. However, there is no need for an enormous amount of synthesis of either of these co-enzymes as there as a mechanism of recycling the co-enzymes after completion of one step in the metabolic pathway. These co-enzymes are predominantly required for the synthesis of ATP (energy currency of the cell) and will be used in the electron transport chain for the production of the same. So, they are not required to be synthesized in huge quantities but they play a crucial role in cell energetics.