Railway Science (Biology – Respiratory System)

Lower invertebrates (sponges, coelenterates, flatworms) exchange O₂ with CO₂ by simple diffusion over their entire body surface. Earthworms use their moist cuticle .
Insects have a network of tubes (tracheal tubes) to transport atmospheric air within the body.
The skin of the earthworm and the frog feels moist and slimy on touching. It is because in earthworms and frogs, exchange of gases takes place by diffusion through the moist body surface.

Aquatic organisms like fishes obtain oxygen from water present in dissolved state through their gills. Whales and dolphins like fishes live in water. But they do not have gills. They breathe through blowholes. Aquatic animals show several adaptations such as streamlined bodies, fins, webbed feet, and air bladder.

Respiration - A metabolic process wherein, the living cells of an organism obtains energy by taking in oxygen and liberating carbon dioxide from the oxidation of complex organic substances.

Types of respiration in humans - Internal respiration (exchange of gasses between blood and cells), external respiration (breathing process) and cellular respiration (metabolic reactions taking place in the cells to produce energy). Aerobic respiration - Glucose is converted into energy in the presence of oxygen. Example: Human respiration. Process involved - Glycolysis → Pyruvate Oxidation → Krebs Cycle→ Electron Transport Chain.

ATP (Adenosine Triphosphate) is an organic compound that provides energy to drive and support many processes in living cells, such as muscle contraction, nerve impulse propagation, condensate dissolution, and chemical synthesis. Pyruvate is a 2 - oxo monocarboxylic acid anion that is the conjugate base of pyruvic acid. Glucose is a ubiquitous source of energy and is essential to fuel both aerobic (Oxygen is used) and anaerobic (Oxygen is not used) cellular respiration.

Composition of Inhaled Air - Nitrogen (78%), Oxygen (21%), Argon (>1%), Carbon dioxide (0.04%). Composition of Exhaled Air - Nitrogen (78%), Oxygen (16%), Argon (>1%), Carbon dioxide (4.4%).

Cilia - The bronchus in the lungs are lined with hair like projections that move microbes and debris up and out of the airways.
Respiratory tract - It has two parts, the upper respiratory tract, consisting of the nose, nasal cavity and the pharynx; and the lower respiratory tract, consisting of the larynx, trachea, bronchi and the lungs.

Respiration is the chemical process by which organic compounds release energy. Respiration occurs in these steps - glycolysis, Krebs cycle (Citric Acid Cycle) and oxidative phosphorylation occurs in the electron transport chain. Glycolysis occurs in both aerobic and anaerobic conditions.
In eukaryotes, the Krebs cycle reactions take place in the mitochondrial matrix and in the final step two molecules of pyruvic acid and two molecules of adenosine triphosphate (ATP) are produced.

Spiracles are small openings present on the sides of the body of insects, like cockroaches. They help in entry and exit of gases for respiration. Trachea are small tubes which form the tracheal system and present in an earthworm.
Gills are branching organs located on the side of fish heads that have many small blood vessels called capillaries. Octopus, Shark and Fish are breathing through gills.

Insects respire through a system of openings on the skin called spiracles. The air enters the body of an insect through spiracles and then is circulated through the network of the tracheae where gaseous exchange takes place directly with the insect tissues.