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Respiratory System of a fish

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.

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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.

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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.


To compare the structure and functions of the organs of the respiratory system.


* Probe

* Scissors

* Gloves

* Cutting board

* Garfish


1. km



Highly efficient respiratory organs which are the site of gas transfer in a fish. Gas is transferred as the water continuously moves over the gill filaments, Transferring oxygen into the bloodstream inside the filament.


Carries the oxygen from the gills around the fish.

Nasal Cavity

Conditions the air and collects dust in the air with minute hairs.


Mainly involved in vocalisation and prevention of food going into the lungs. Attached to it is the epiglottis, which closes over the trachea to stop food going in.


Mainly involved with vocalisation again, it closes while swallowing so as to not let food into the lungs.


Contains smooth muscle. The path which air travels along to reach the alveoli.


The site of gas exchange in the human body, round spherical ball, 1mm in radius.


The main organ of the respiratory system which allows for oxygen to be diffused in the alveoli so each person can make ATP through cellular respiration


Strong dual muscles which pushes the lungs up to receive oxygen for cellular respiration


Because of the fluidity of the water, the fish is easily able to retrieve oxygen in the water by letting the water run through the mouths and extracting oxygen. The water can easily flow to the lamella and diffuse across the bloodstream, going directly to the blood rather than having to go through all of the pipes and tunnels in human lungs to receive oxygen. The gas exchange is continuous for fish, whereas humans have to constantly breathe to receive oxygen. Also, in the lamellae the blood is flowing in one direction, yet the water runs in the other.

This is called a counter current system. This means gas exchange can occur continuously, rather than having to wait for more deoxygenated blood for the oxygen to diffuse into. Another reason why its structure is suited to gas exchange is that when it opens its mouth, water flows in, and when it closes its mouth, the water filters out of the gills, with all of the oxygen being diffused on the way out of the gills.

The journey of an oxygen molecule from water to the fish is quite quick. The oxygen molecule floats into the path of the fish. As the fish approaches, the oxygen molecule still moves with the current. When the fish opens its mouth, all of the water filters in, including the oxygen molecule. The oxygen flows into the gill arches, passing back and forth the gill bars and filaments. Then the oxygen diffuses into the bloodstream.

Similarities between Fish and Human respiration.

Differences between Fish and Human respiration.

Fish and Human respiration both involve oxygen.

Garfish don’t possess lungs, Humans possess lungs.

Fish and Human respiration both occurs after oxygen passes through their mouths.

Garfish gain their oxygen from the water, Humans gain their oxygen from the air.

Both forms of respiration occur along a concentration gradient.

Humans’ respiratory system is much longer, having to go into a lung, then further until you reach the alveoli. Garfish respiratory cycle is much quicker.

Garfish have counter current oxygen supplying them with oxygen, whereas humans need to inhale to receive oxygen.

Garfish possess gills, Humans don’t possess gills.

Animals very different and unlike each other have very different organ systems, especially respiratory. Salamanders have their gas exchange occur across their skin and through the use of lungs, which is useful as they can keep the lungs as storage while they breathe through their skin. Amphibians also breathe through their skins, but they can also breathe through their lungs and gills, which means they can swim and keep air in the lungs for backup, while they breathe in oxygen from the water. Although, amphibians do not breathe the same way as humans through their lungs, as they don’t have diaphragms, so they need to ‘swallow’ the air.

Gas exchange occurs with insects as well, between their tissue in air filled tubes. The way air gets into their tissue is through spiracles. They are minute holes which insects can open and close themselves to allow air in sometimes. Gas exchange is rather simple, just diffusing into the bloodstream, but in some environments, gas exchange results in a loss of water vapour, capable of killing an insect quickly in a dry environment. This proves there are way o get rid of annoying insects.

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Respiratory System of a fish. (2020, Jun 02). Retrieved from

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