Mechanism Of Respiration In Lower Organism

Oxygen intake and expulsion of carbon(iv)oxide in unicellular organism is by diffusion through the entire body surface.

Oxygen needed for respiration is dissolved in water. Based on the principle that molecular gasses will diffuse from a region of higher concentration to region of lower concentration, dissolved oxygen which is of higher concentration in water than in the cell will diffuse into the cell. After gaseous exchanges, carbon(iv)oxide which is now higher in concentration in the cell than in water will diffuse out of the cell into the water.

Exchange of gases takes place in the ectoplasm of unicellular organism e.g. Amoeba, paramecium and euglena.

OrganismsRespiratory surfaceFunctioning Environment
Amoeba & paramecium (unicellular)Cell membraneAquatic
Molluscs, fishes, tadpoles and crustaceanGillsAquatic
Frogs, toads and earthwormTracheaeTerrestrial
InsectsReptiles, birds and mammalsLungsTerritorial
Frog and toadLeavesStemMouthStomataLenticelsTerrestrialTerrestrialTerrestrial

Mechanism of Respiration in insects

The respiratory organ in insect is the trachea system which is used for gaseous exchange. The insect has a tiny openings in their abdomen called spiracles through which oxygen diffuse into the body and CO2 diffuses out. The spiracle lead to a certain tube called tracheae which further divide into a smaller tube called tracheae and these tiny tubes are in contact with body tissues and body fluid.

Oxygen for respiration enter the abdomen and thoracic segment from surrounding atmosphere. The expansion of the abdomen cause the volume of the abdomen is increase thereby drawing air by diffusion into the body through the spiracles, tracheae, air sacs and trachioles. When the atmosphere oxygen reaches the fluid of the trachioles, it dissolves. The dissolved oxygen then diffuses into the tissues where cellular or tissue respiration. When the thoracic segments and abdomen contract, carbon(iv)oxide and water vapour diffuse from spiracles into the atmosphere.

Mechanism of respiration in fishes

The organ of respiration is the gills which are used for gaseous exchange. The gills are located of both sides of the head region. The gills which arranged in the gill chamber gills chamber. Each gill chamber is closed externally by operculum.

Gaseous exchange or breathing occurs across the gills surface. All the gills possess a very high surface area to volume ratio.

The fish opens its mouth and water rushes over the gills surface inside the opercula which are closed. As water flows over the gills, the dissolved oxygen in the water diffuses into the thin walled blood capillaries of the gills. At the same time, carbon(iv)oxide in the blood diffuses into the water. The alternate opening and closing of the mouth and opercula allow a constant flow of water over the gills. Oxygen is transported by the blood into every living cell where it is used for aerobic respiration. Hence, the gills are used for gaseous exchange or breathing and not for respiration.

Mechanism of respiration in Toad or Frog

  1. Adult amphibians (toad and frog) breathe in three ways: through their skin (cutaneous breathing), through their mouth (buccal breathing) and through their lungs (pulmonary breathing).

Cutaneous respiration –The adult toad is capable of carrying out respiration using the skin both on land and in water. The toad skin is moist because it contains numerous glands which secrets a watery shine onto the surface so that gases can diffuse through it. The skin is also thin-walled and well-supplied with blood vessels to quicken the rate of diffusion of gases in and out of it.

Buccal respiration: The toad is capable of respiration by mouth when on land to serve as an efficient respiratory organ. To breathe with the mouth, the mouth is closed, the nostrils are opened and the buccal cavity floor is lowered by muscular action. The buccal cavity volume increases, its air pressure decreases and air is drawn through the nostrils. Oxygen in the air diffuses into the lining of the buccal cavity which is well-supplied with blood capillaries when the nostrils are used. In exchange, CO2 from the blood capillaries is given off by diffusion. The buccal cavity floor is raised, its air pressure increase and so air containing a lot of carbon(iv)oxide and water vapour is expelled through the nostrils.

Lungs or pulmonary respiration: The toad and frog uses their lungs for breathing only on land when it is very active and demand for oxygen is high. Air is drawn into the buccal cavity and the nostrils are closed. The buccal cavity floor is raised and air is expelled through the larynx into alveoli of the two lungs in which gas exchange occurs. The alternate raising and lowering of the buccal cavity ensures that air is forced into and out of the lungs. Air is expelled through the nostrils when they open, while the contraction of the lungs also aids the sending out air.

Respiratory system of man

The respiratory system in man includes the nasal passage or nostrils, pharynx, larynx or voice box, trachea or windpipe, bronchus, bronchioles and alveoli. The nostrils lead into the posterior position of the mouth cavity called pharynx and this leads into voice box or larynx. The larynx leads into the windpipe or trachea. A flat piece of tissue called epiglottis cover the entrance to the larynx and trachea when swallowing food. The trachea branches into two bronchi. Each bronchus leads to the lungs where it branches into small tubes called bronchioles. The bronchioles lead to numerous air sac called alveoli.

The alveoli are richly supplied with blood capillaries and are sites or surface where gaseous exchange takes place.

Mechanism of respiration in man

The mechanism of breathing in mammals involves two phases. These are external and internal respiration.

External respiration or breathing is defined as the exchange of gases between the environment and the respiratory organ of the living organism. External respiration involves two processes inspiration or expiration.

INSPIRATION OR INHALATION: This is the breathing in of oxygen into the lungs. The followings take place during inspiration.

  1. The thoracic cavity first increases in volume
  2. The diaphragm contracts and becomes flattened
  • The intercostal muscles contract
  1. The sternum move forward
  2. The ribs are moved upwards and outward
  3. The thoracic cavity increases in volume but the pressure decreases, air from outside is drawn into the lungs or alveoli through the nose, trachea, bronchi and bronchioles leading to an increase in the size of the lungs.

EXPIRATION OR EXHALATION: This is the breathing out of CO2 and water vapour into the atmosphere or environment. The following processes takes place during expiration.

  1. The thoracic cavity first decreases in volume
  2. The diaphragm relaxes and assume its dorm shape.
  • The intercostal muscles relax
  1. The sternum moves inward
  2. The ribs are moved downward and inward.
  3. The thoracic cavity decreases in volume and the pressure increases, this cause air containing waste products like CO2 and water vapour from inside alveoli of the lung to be forced our through bronchioles, bronchus, trachea and finally to the outside through the nose.

Internal / Tissue / Cellular respiration is defined as a chemical activities of the cells in which glucose is broken down using oxygen by a series of reactions controlled by enzymes to release energy. The energy released is stored in adenosine triphosphate (ATP).

ATP is the form in which energy is carried, stored and used by all living cells for various metabolic activities.

The lungs occupy the thoracic cavity from the shoulder to the diaphragm. It overlaps the heart. It is spongy and surrounded by an elastic membrane called pleural membrane which allows stretching.

Mechanism of gaseous exchange in leave

The green plants respire along with photosynthesis during the day light. During respiration, plant take in air form their surroundings, use the oxygen of the air to breakdown stored food for the purpose of energy production and release carbon(iv)oxide and water.

In simple aquatic plant such as spirogyra, dissolved air/oxygen in water diffuses into the cells through the general body surface but in vascular or higher plant atmospheric air enters through stomata of the leaves and lenticels of the stem through the process of diffusion. Due to differences in concentration gradient, oxygen is taken in through the stomata and lenticel especially during the night and CO2 and water are given out.

But during the day, when photosynthesis is going on, oxygen and vapour from photosynthesis diffuse out to the exterior through the stomata and lenticels. The opening and closing of the stomata is controlled by the guard cells. Turgidity of guard cells quicken the opening stomata while the flaccidity of the guard cell cause the closing of the guard cells.

Oxygen debts is defined as the quick breathing to take oxygen to the muscle cells lacking oxygen in other to oxidize the lactic acid build up in the muscle.

 (Causes of oxygen debt OD)

  1. Vigorous exercise leading to shortage of oxygen in muscle cells
  2. Lungs unable to meet the demand of oxygen in the cell of muscles
  3. The cells of the muscles have to respire aerobically producing lactic acid little energy.
  4. Lactic acid accumulation in the muscle cells
  5. After vigorous exercise, the lactic acid remains in the muscle cell resulting in muscle fatigue and aches
  6. More oxygen is then required to repay the debt of oxygen in the muscle cells.

When sufficient oxygen is breathed in to oxidize the lactic acids, the debt has been paid.

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