 As-salamu alaikum. In this lecture, we are going to talk about respiration and respiratory systems. First of all, why respiration? What is the need of respiration? As we know that organisms, the living organisms, needs energy for their requirements. They have to always conduct metabolic reactions, catabolism, anabolism. As we know that catabolism is a breakdown of materials to produce energy, anabolism, the reactions for production. All the catabolic reactions and anabolic reactions, the energy producing reactions and the metabolic reactions somewhere needs a gas exchange. There are lot many gases are involved which have to be transported from outside the body to inside or inside to outside and so on. Respiration is a complex process and we divide the respiration into two major forms, two major types, cellular respiration and the organismic respiration. What is respiration? If we precisely define it, this is a process which involves exchange of gases in living organisms. Respiration is one of the most important functions in the living organisms. This is of two types as I previously said, cellular respiration and organismic respiration. Cellular respiration is the respiration at cell level. In the cell, there are energy producing reactions which starts from usually breakdown of a glucose molecule into smaller materials, into smaller molecules resulting in a release of carbon dioxide and production of energy. Some processes which are involved are called glycolysis, electron transport chain, crab cycle and so on. We call this process, all of these processes, cellular respiration. The other one is organismic respiration. Organismic respiration is actually, in other words, breathing or ventilation, the breathing movements. The movements of body which causes the inhalation or influx of air inside the body and then removal of air from the body after some time and during this time, the exchange of gases takes place. So, respiration is of two kinds, cellular respiration and organismic respiration. And cellular respiration also consists of two types which are aerobic respiration and anaerobic respiration. Anaerobic respiration in which oxygen is utilized. Oxygen is required for the metabolic processes involved in aerobic respiration while in anaerobic as the name says anaerobic, oxygen is not required. These processes takes place without the presence of oxygen. There are few organisms that conduct this anaerobic respiration, mostly prokaryotes for example bacteria, they conduct anaerobic respiration and even oxygen if they have to live in an environment where there is oxygen present, they are killed because they do not have certain enzymes to handle with the oxygen, with the presence of oxygen because due to some metabolic reactions, they produce some toxic products in presence of oxygen and they cannot break down those toxic products. This is the reason that these organisms cannot survive in oxygen, we call them obligate anaerobics. Even in some parts of human body, the anaerobic respiration occur in our muscles. Sometimes when our blood is not sufficient, for example we are exercising and our blood supply is not sufficient to provide enough oxygen to our exercising muscles, then these muscles have a capacity to conduct an anaerobic respiration to produce their energy. But usually the result of this energy is because the products of anaerobic respiration are usually acids and alcohols, lactic acid is produced in our muscles and if we continue this activity, this exercise for a longer period for example in sportsmen, this may result in lactic acid accumulation in the muscles which usually causes us pain in our muscles after exercise. So, this is the difference between cellular respiration and organismic respiration. In this lecture, we are concentrating more on the organismic respiration, how the guesses are exchanged from environment to organism and from organism to environment and on different surfaces inside the organism which are made for the gaseous exchange. We know that organisms are aquatic or terrestrial, some organisms lives in water, we call them aquatic, some organisms live on land, we call them terrestrial, for example fish are aquatic organisms, the lions for example are terrestrial organisms. There is a difference between the respiration on water and on land, water is much denser in comparison to air, about 8000 times more denser, air is very light, air is much more saturated with oxygen in comparison to water, it means that air have more oxygen present in it in comparison to an equal volume of water. That is why respiration in air is comparatively easier to access for the organisms and the mechanisms are also comparatively simpler or easier. Now we look at respiration in different organisms, in plants, plants also conduct a process of respiration, in plants gaseous exchange occur by stomata in the mesophyll cell, mostly in the mesophyll cell layer there are openings called stomata, stomata, lural and stoma singular, for example a surface of a leaf have many stomata on its lower layer, in the mesophyll cell, these stomata are openings which are supported or around which present are some cells called guard cells, when these cells swell up, the opening is, the pathway of opening is open and exchange of the gaseous can take place, when these guard cells shrink and again they shrink, then the result is stomata are closed, plants also have to, the plant roots also have to exchange gaseous, as we know that plant roots, these are present inside the soil mostly, though there are certain roots which are sometimes on the branches, but the roots in the soil have to absorb oxygen from soil, as we know that soil particles have certain pores in them, in these pores oxygen is present, roots absorb oxygen from the soil, just like that aquatic plants absorbs oxygen from their surrounding water, have a look on the diagram, which shows that there is a change of water, oxygen and carbon dioxide from the leaves, roots are absorbing, roots includes the tubers, which are the extended parts for example, the potatoes, they also absorb oxygen, water and minerals and other materials, the gaseous like carbon dioxide with the soil, in animals respiration is comparatively a more complex process, animals, the most important thing for the exchange of gaseous in animals is the respiratory surface, on what surface, an epithelium, a linen or any place, lungs or gills, where the exchange of gaseous occur, exchange of gases occur on a respiratory surface, to be a respiratory surface, the animals parts of the body, surfaces should have certain qualities, that surface should be very large, that is should have a very large surface area, for example, the lungs in human beings, this should be moist, this should be kept moist for the exchange of gaseous, for the ease of exchange, these surfaces should have a very thin epithelium, because gaseous has to be exchanged with the tissues and the blood cells, so there should be a very thin layer between the blood cells and the tissues, so thin epithelium is the second property, then capillary network, the respiratory surfaces should have an extensive capillary network, because exchange of gaseous takes place with the help of capillaries, which are so thin, we know that capillaries are so thin that they just consist of endothelium, that is a single layer of cells, the respiratory surface should also have a single layer of cells, so that exchange between the blood cells and between the air, exchange of gases, carbon dioxide, oxygen, whatever should easily occur, so these are some specific properties of the respiratory surfaces. Now, we are going to talk about respiration in some small animals and in some large animals, just briefly, here we can see in the slide, there are three small animals, Hydra, an insect and earthworm, Hydra is a very simple organism, as we know that as simple, as simpler the organization is, as simple the processes are, in Hydra there is just one cavity inside the body called body cavity or a gastro vascular cavity, as you can see in the diagram and there is only one opening mouth, water enters through mouth inside the gastro vascular cavity and the exchange of gases takes place with the inner layer of cell, the cells, the endoderm, the outer surface of the Hydra also can exchange gases with the medium, because they are aquatic and they live in water, so respiration in these organisms is simpler. Look at the next diagram of an insect, this diagram shows that insects have a more complicated, but a very efficient system of respiration, they have a system of tubes canals which is called a tracheal system, these tubes are called trachea, they have openings from the body surface and through openings, there are cuticle lined canals, which are moving in a very regular fashion throughout the body, almost transfers from the body that is from one abdominal side to the other side, from left side to the right side and so on and up to thorax. These canals because they are open directly to exterior, air can directly enter inside, so these canals can have air inside through the openings, these openings called spiracles, then the air can move out by a contraction of the muscles of abdominal cavity. This system is very efficient because these tubes move around and go close to almost all tissues of the body and medium is simply the air inside the tubes, so exchange of gases could easily occur, this is a very efficient system of respiration. In earthworm, however, there are different canals, respiratory vessels which are present near to the surface of the body, so the exchange of gases could easily take place directly through epithelium because the blood vessels are so close to the epithelium and epithelium is thin, they can easily exchange gases through epithelium towards blood and back, so in simpler organisms respiration at organismic level is simpler. Let us talk about some larger organisms, fish, frog and birds. Let us look at another diagram, here you can see a fish, fish as we know lives in water, they have to exchange their gases with water and not with the air, they have also a very efficient system for extracting oxygen and other gases and removal of these gases, the metabolic waste products in their body and this system is called system of gills, the gills are actually surfaces, the respiratory surfaces, water as you can see in the diagram enters through the mouth and passes through the gills, the gill arches and the gill aparcula, the gills actually, the gill filaments, actually the gill consists of five to six filaments present on both sides of the head just behind the eyes and these are richly supplied with blood vessels, when the water moves through mouth and passes through gills because gills are richly supplied with blood vessels, the exchange of gases takes place here, the fish have a single circuit heart, their heart pump their blood towards the gills, the gill filaments and when this blood passes through the gill filaments exchange of gases takes place because that blood was the oxygenated blood which is coming from the body in the heart and from heart to the gills, from gills blood goes directly back to the body and do not come back inside the heart as in the other vertebrates in the case of heart and lungs system. So, we call it single circuit heart that is heart receives blood from the body, contract and send it to the gills, gills are richly supplied with the blood vessels and water passes through these gills in larger quantities, the exchange of gases takes place there on the gill filaments. Here a frog, frogs have two systems of respiration, one is the pulmonary with the help of lungs and other is to skin, cutaneous respiration, frogs as we know are a transition between the water, water living that is aquatic and land animal, frogs have lungs and how you can see in the diagram in a very simple way that air enters through the nostrils, go inside the buccal cavity and when air enters through nostrils the buccal cavities floor is raised that is moves towards, moves upward, move upwards the result is that air goes directly inside the lungs and lungs are inflated, lungs are again richly supplied with blood vessels and exchange of gases takes place. Then frogs also have another type of respiration called cutaneous respiration, their skin is richly supplied with blood vessels and because these blood vessels are directly related to skins, they are directly attached to the skin they can easy, there could be a very easy exchange of gases that takes place, we call it a cutaneous respiration. So, frog have two types of respiration, cutaneous respiration and pulmonary respiration with the help of lungs. Next we talk about birds, birds have very high metabolic rate, birds have to maintain their metabolism at a very high rate because they need lots of ATP molecules for particularly their flight activity, they have more specifics type of respiratory system. Look at a diagram, it shows you that birds have lungs which are very efficient lungs plus these lungs their surfaces, these respiratory surfaces are extended in the form of air sacs in the body, these air sacs even sometimes penetrate their bones, birds have a very high capacity for acquiring oxygen from environment, oxygen enters into lungs and the exchange of gases takes place, oxygen enters into the air sacs, fill the air sacs as you can see in the diagram and this air is also used for the exchange of gases, the birds have a very efficient system of exchange of gases.