BIOLOGY SAC: PRACTICAL REPORT
THE RESPIRATORY SYSTEM OF A FISH
PREPARED BY SARANG PALERI
INTRODUCTION:
The respiratory system is an intricate structure existing in most forms of life, which allows for these organisms to take air into their bodies for cellular respiration to take place inside cells, as the name suggests. Cellular respiration is the oxidation of organic compounds that occurs within cells, producing energy for cellular processes. In humans, glucose is the ‘fuel’ molecule, which is oxidised by oxygen, producing carbon dioxide, water and energy. The formula is this:
C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l) + 36ATP
ATP is utilisable energy in the form of a molecule. It is very vital to the human body, as it provides energy to the many functions that our bodies perform in a day. ATP provides energy for muscle contraction on skeletal and heart muscle, and the diaphragm and the muscle in the gut. The muscle is able to move easily because of the body’s large ATP supply. ATP also puts in energy to manufacture chemicals, like blood proteins, hormones and enzymes. It provides energy to the excretory system and the digestive system, and to the nervous tissue, so it can efficiently conduct impulses from other neurons, and send neurotransmitters between neurons. ATP is vital to bodily function; therefore respiration is an incredibly important part of human survival. For respiration to occur, the body needs to receive oxygen from the atmosphere, which is does through the respiratory system.
As humans inhale, they take in air, which consists of predominantly nitrogen and oxygen. Inhalation is initiated by the diaphragm, by intercostal muscles. When this occurs, the body’s ribcage enlarges, with the lungs expanding and pushing the contents of he abdomen downwards. Inhalation occurs around 10 to 18 times a minute, but increases while vigorous activity is being performed. As they inhale, the oxygen and nitrogen comes into the body, through the nose or mouth. When it comes through the nose, it enters a nasal cavity. The nasal cavity neutralises the temperature of the air to approximately body temperature. The air is also filtered, any dust or particles being caught by the hairs in the nasal cavity. The air flows through the pharynx and larynx into the bronchi. The bronchi leads to the secondary bronchus, which leads to the bronchiole, which leads to the terminal bronchiole onto the respiratory bronchiole. As the air gets further into the lungs, the path gets smaller and smaller, especially in the bronchi and bronchioles. Finally, the respiratory bronchiole leads into alveolar duct, which contains alveolar sacs and alveoli. Alveoli are small pouches where gas exchange occurs in the human body. There are around 300 million in the two lungs. They are spherical structures inside alveolar sacs, and are covered in pulmonary arteries and veins, to transport oxygen from the lungs to the heart, and to transport carbon dioxide out of the lungs into the air. Air readily diffuses into the alveoli wall, and due to the concentration gradient, requires no energy to diffuse into the bloodstream through the pulmonary veins. The reason there is a concentration gradient is because there is a high concentration of oxygen in the alveoli and a low concentration in the bloodstream, as oxygen is continuously being consumed by the body. At the same time, carbon dioxide is being diffused out of the blood, into the alveoli and lungs, to be exhaled into the atmosphere. This is how gas exchange occurs in the lungs of the human body.
