how are fish gills adapted for gas exchange

Previously, the evolution of gills was thought to have occurred through two diverging lines: gills formed from the endoderm, as seen in jawless fish species, or those form by the ectoderm, as seen in jawed fish. This cookie is set by GDPR Cookie Consent plugin. The main function of gas exchange is to bring oxygen into the tissues and expel carbon dioxide. Within the gill filaments, capillary blood flows in the opposite direction to the water, causing counter-current exchange. Valves inside the mouth keep the water from escaping. The buccal cavity of the electric eel may breathe air. Born and raised in the city of London, Alexander Johnson studied biology and chemistry in college and went on to earn a PhD in biochemistry. [8] Water is 777 times more dense than air and is 100 times more viscous. Rich blood supply of lamellae. Search. Some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods. 3 (pp. The vertebrate ancestor no doubt had more arches, as some of their chordate relatives have more than 50 pairs of gills. Chronic obstructive pulmonary disease. Gills, like lungs, have a huge surface area for gas exchange. In the gill lamellae the blood flows towards the front of the fish while the water flows towards the back. The arrangement of water flowing past the gills in the opposite direction to the blood (called countercurrent flow) means that they can extract oxygen at 3 times the rate a human can. Loaches, trahiras, and many catfish breathe by passing air through the gut. Explain. Explain how the gills of a fish are adapted for efficient gas exchange? Theory. Though all but the most primitive bony fish lack a spiracle, the pseudobranch associated with it often remains, being located at the base of the operculum. They control water loss and gas exchange by opening and closing. The second mechanism includes the moving of water over the gill. (accept more oxygen), AQA Gaseous Exchange (No Plant) | Maths and P, Exchange surfaces in fish and insects PPQ AQA, Biology - Unit 1 - Chapter 4 - Lungs and Lung, David N. Shier, Jackie L. Butler, Ricki Lewis, John David Jackson, Patricia Meglich, Robert Mathis, Sean Valentine, Microbiology Midterm Questions - Jersey Colle. the large surface area of the blood capillaries in each gill filament. 721 \text { torr } & 141 \mathrm{~mL} & 135 \mathrm{~K} & 801 \text { torr } & 152 \mathrm{~mL} & -\\ Lra has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning. The skin of anguillid eels may absorb oxygen directly. Learn without limits Explainer videos without evulpo advertising. (2), What causes the pressure difference to fall below zero? However, if a fish swims forward with its mouth open, water will flow across the gills without active pumping by the muscles surrounding the buccal and opercular cavities. 1. mouth opens, operculum/opercular valve shuts; There is a one-way flow of water over the gills of a fish whereas there is a two-way flow of air in the lungs of a mammal. Objective, Importance and Limitations of Animal Breeding. The gaseous exchange takes place between alveoli in the lungs and blood capillaries. The fish opens its mouth to let water in, then closes its mouth and forces the water through the gills and out through the operculum (gill cover). Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. The gills (found under the gill covers) allow the fish to breath. Position of gill arches beneath the operculum on the left side of fish. Seawater contains more osmolytes than the fish's internal fluids, so marine fishes naturally lose water through their gills via osmosis. Water must flow through the gills so that the oxygen in the water can diffuse into the blood around gills and circulate through the fish. Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. The cookie is used to store the user consent for the cookies in the category "Analytics". lamellae / m Number of lamellae Alveoli in the lungs, fish gills and the villi in the small intestine are adapted so that they have short diffusion distance, big concentration difference and large surface area. Amphibious fish such as the mudskipper can live and move about on land for up to several days, or live in stagnant or otherwise oxygen depleted water. Thickness of (1). Genetics, Populations, Evolution & Ecosystems (A Level only), 7.1.2 Predicting Inheritance: Monohybrid Crosses, 7.1.3 Predicting Inheritance: Dihybrid Crosses, 7.1.4 Predicting Inheritance: Test Crosses, 7.3.8 Investigating the Effects of Random Sampling on Allele Frequencies, 7.4 Populations in Ecosystems (A Level only), 7.4.4 Estimating the Size of a Population, 8. Breathing air is primarily of use to fish that inhabit shallow, seasonally variable waters where the water's oxygen concentration may seasonally decline. This is, however, often greatly reduced, consisting of a small mass of cells without any remaining gill-like structure.[7]. the short distance required for diffusion the outer layer of the gill filaments and the capillary walls are just one cell thick. The volume of the buccal cavity can be changed by lowering of the jaw and the floor of the mouth. This allows for more efficient gas exchange than if the water had to go in and out the same way. Oxygen and carbon dioxide are exchanged in a process of simple diffusion; (passive movement from high to low concentration) The air in the alveoli contains a high concentration of oxygen. Air-breathing fish have skin, lungs, or air bladders that enable gas exchange with surface air in addition to gills. The volume of the opercular cavity can also be changed by the movements of opercular flaps that swing out to enlarge the cavity and swing in to reduce it. The first, titled Arturo Xuncax, is set in an Indian village in Guatemala. Lra graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. The graph shows the difference in pressure between the mouth cavity and the opercular cavity. Their kind of gill respiration is shared by the "fishes" because it was present in their common ancestor and lost in the other living vertebrates. Gills are highly folded, giving them a large surface area and maximising the efficiency of gas exchange. Fish use gills for gas exchange. Also covered by the video includes how the fish draws water into its mouth and over its gills. In this method, much force is needed to overcome the resistance of water in order to permit the movement. A proton is released from rest at the positive plate at the same instant an electron is released from rest at the negative plate. This means that fresh water, high in oxygen is always [passing the gills and there is a steep diffusion gradient for oxygen between water and the blood, Michelle Provost-Craig, Susan J. After many, many years, you will have some intuition for the physics you studied. Fish from multiple groups can live out of the water for extended time periods. Join MyTutor Squads for free (and fun) help with Maths, Coding & Study Skills. aquarium DO NOT WRITE IN THIS AREA DO NOT WATE IN THIS AREA arator One-to-one online tuition can be a great way to brush up on your Biology knowledge. a Fantasy Oxygen is a product of photosynthesis it is needed as a reactant during aerobic respiration within a plant. Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. Fish and many other aquatic organisms have evolved gills (outgrowths of the body used for gas exchange) to take up the dissolved oxygen from water. More complex or more active aquatic organisms are possessed by more elaborate gill structure as they require more oxygen. Oxygenated blood is continuously removed from the gills by the circulation to the rest of the body. #gcsebiology #gcsefishgills #biologydissection #AlevelbiologyTimestamps: 0:00 - introduction 0:20 - Ram Ventilation0:55 - Drawing Water Through The Gills1:55 - Gill Structure2:39 - Counter Current Mechanism3:41 - Gills UnderwaterExam Questions:A-level Biology - Gas Exchange Questions - shorturl.at/bLYZ4 Mark Scheme - shorturl.at/otyLW 3.1.5 Adaptations of Gas Exchange Surfaces. This continues until the water and the blood have reached equal saturation. Exercises. The complexity of the gills depends on the animals requirement for oxygen. Just a click away. Always. A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water and excretes carbon dioxide. How do gills promote rapid gas exchange by having a good oxygen supply? 1. Toadfish live on the seabed in deep water. But based on this shared trait, we cannot infer that bony fish are more closely related to sharks and rays than they are to terrestrial vertebrates. Fish extract dissolved oxygen molecules from the surrounding water. To see how the gas exchange happens, we need to zoom right in on a single lamella. This happens in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli. It ensures the maximum exchange possible occurs. EVOLUTIONCONNECTION\text{\blue{EVOLUTION CONNECTION}}EVOLUTIONCONNECTION Living members of a vertebrate lineage can be very different from early members of the lineage, and evolutionary reversals (character losses) are common. [7] The spiracle is thought to be homologous to the ear opening in higher vertebrates. The ventilation mechanism in fish constantly pushes water over the surface of the gills and ensures they are constantly supplied with water rich in oxygen (maintaining the concentration gradient) When the fish open their mouth they lower the floor of the buccal cavity. 1.1.10 Biochemical Tests: Sugars & Starch, 1.1.11 Finding the Concentration of Glucose, 1.3.7 The Molecular Structure of Haemoglobin, 1.3.8 The Molecular Structure of Collagen, 1.4.4 Required Practical: Measuring Enzyme Activity, 1.4.5 Maths Skill: Drawing a Graph for Enzyme Rate Experiments, 1.4.6 Maths Skill: Using a Tangent to Find Initial Rate of Reaction, 1.4.7 Limiting Factors Affecting Enzymes: Temperature, 1.4.8 Limiting Factors Affecting Enzymes: pH, 1.4.10 Limiting Factors Affecting Enzymes: Enzyme Concentration, 1.4.11 Limiting Factors Affecting Enzymes: Substrate Concentration, 1.4.12 Limiting Factors Affecting Enzymes: Inhibitors, 1.4.13 Models & Functions of Enzyme Action, 1.4.14 Practical Skill: Controlling Variables & Calculating Uncertainty, 1.5 Nucleic Acids: Structure & DNA Replication, 1.5.2 Nucleotide Structure & the Phosphodiester Bond, 1.5.6 The Origins of Research on the Genetic Code, 1.5.8 The Process of Semi-Conservative Replication, 1.5.9 Calculating the Frequency of Nucleotide Bases, 2.2.2 Microscopy & Drawing Scientific Diagrams, 2.2.6 Cell Fractionation & Ultracentrifugation, 2.2.7 Scientific Research into Cell Organelles, 2.3 Cell Division in Eukaryotic & Prokaryotic Cells, 2.3.7 Uncontrolled Cell Division & Cancer, 2.4.2 Components of Cell Surface Membranes, 2.4.8 Comparing Osmosis in Animal & Plant Cells, 2.4.13 Factors Affecting Membrane Fluidity, 2.5.5 The Role of Antigen-Presenting Cells, 2.6 Vaccines, Disease & Monoclonal Antibodies, 2.6.6 Ethical Issues with Vaccines & Monoclonal Antibodies, 3.2.3 Looking at the Gas Exchange under the Microscope, 3.2.11 Correlations & Causal Relationships - The Lungs, 3.4.7 Animal Adaptations For Their Environment, 3.5.8 Interpreting Data on the Cardiovascular System, 3.5.9 Correlations & Causal Relationships - The Heart, 3.5.10 Required Practical: Dissecting Mass Transport Systems, 4.2.6 Nucleic Acid & Amino Acid Sequence Comparison, 4.3 Genetic Diversity: Mutations & Meiosis, 4.3.5 Meiosis: Sources of Genetic Variation, 4.3.7 The Outcomes & Processes of Mitosis & Meiosis, 4.4.2 Maths Skill: Using Logarithms When Investigating Bacteria, 4.4.4 Directional & Stabilising Selection, 4.6.7 Quantitative Investigations of Variation, 4.6.9 Genetic Relationships Between Organisms, 5. This counter current system increases the concentration gradient and increases the efficiency of gas exchange. They continuously pump their jaws and opercula to draw water in through the mouth and then force it over the gills and out through the opercular valve behind the gills. A few other fish have structures resembling labyrinth organs in form and function, most notably snakeheads, pikeheads, and the Clariidae catfish family. Explain the functional adaptations of gas exchange surfaces in animals using Fick's Law (surface area, distance, concentration gradients and perfusion) . Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. [12] These are reduced in adulthood, their function taken over by the gills proper in fishes and by lungs in most amphibians. 5.51 \mathrm{~atm}& 0.879 \mathrm{~L}& 22.1^{\circ} \mathrm{C} & -& 1.05\mathrm{~L} & 38.3 { }^{\circ} \mathrm{C}\\ (1) REFER TO DIAGRAM, Explain the relationship between gill surface area and swimming speed. The individual lamellae of the gills lie on either side of the septum. Adaptations of Gas Exchange Surfaces Effective exchange surfaces in organisms have: A large surface area Short diffusion distance Concentration gradient (maintained) Across the Body Surface of a Single-celled Organism Chlamydomonas is a single-celled organism that is found in fresh-water ponds. You also have the option to opt-out of these cookies. Abstract. (2008). the efficient ventilation of the gills with water - there is a counter current flow of water and blood The moving blood and ventilated gill surfaces mean that gases exchanged are continually. There are blood vessels running through a structure called the gill arch which deliver and remove blood. Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills.The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Fish also have an efficient transport system within the lamellae which maintains the concentration gradient across the lamellae. [7], The gill arches of bony fish typically have no septum, so that the gills alone project from the arch, supported by individual gill rays. A fish uses its gills to absorb oxygen from water. Part of two adjoining gill arches with their filaments. The structure of the gills (filaments, lamellae) as well as the counter current mechanism in fish for maintaining a large concentration gradient. A. The gill cover is open when the mouth is closed. [7], The shared trait of breathing via gills in bony fish and cartilaginous fish is a famous example of symplesiomorphy. Leeches, Lice and Lampreys. [7] Fish gill slits may be the evolutionary ancestors of the tonsils, thymus gland, and Eustachian tubes, as well as many other structures derived from the embryonic branchial pouches. \end{array} Squamous epithelium of alveolar wall, endothelium of blood capillaries in alveoli and basement substance are the three layers forming diffusion surface or membrane. 8 study hacks, 3 revision templates, 6 revision techniques, 10 exam and self-care tips. Wittenberg is a nationally ranked liberal arts institution with a particular strength in the sciences. Water taken in continuously through the mouth . Alveolar number was closely related to total lung volume, with larger lungs having considerably more alveoli. They create a mass flow of air into the tracheal system by: Using muscles to create a pumping movement for ventilation, Also, during flight the water found at the narrow ends of the tracheoles is drawn into the respiring muscle so gas diffuses across quicker, A given volume of air contains 30 times more oxygen than the same volume of water, Fish are adapted to directly extract oxygen from water, On the surface of each filament, there are rows of, The lamellae surface consists of a single layer of flattened cells that cover a vast network of, The capillary system within the lamellae ensures that the blood flow is in the opposite direction to the flow of water - it is a, The counter-current system ensures the concentration gradient is maintained along the whole length of the capillary, The water with the lowest oxygen concentration is found adjacent to the most deoxygenated blood, In order to carry out photosynthesis, plants must have an adequate supply of carbon dioxide, Leaves have evolved adaptations to aid the uptake of carbon dioxide, Upper epidermis - layer of tightly packed cells, Palisade mesophyll layer - layer of elongated cells containing chloroplasts, Spongy mesophyll layer - layer of cells that contains an, Stomata - pores (usually) on the underside of the leaf which, Guard cells - pairs of cells that control the opening and closing of the stomata, Lower epidermis - layer of tightly packed cells, When the guard cells are turgid (full of water) the stoma remains open allowing air to enter the leaf, The air spaces within the spongy mesophyll layer allows carbon dioxide to rapidly diffuse into cells, The carbon dioxide is quickly used up in photosynthesis by cells containing chloroplasts - maintaining the concentration gradient, No active ventilation is required as the thinness of the plant tissues and the presence of stomata helps to create a short diffusion pathway. Repeat part (a) for a sodium ion (Na+)\left(\mathrm{Na}^{+}\right)(Na+) and a chloride ion (Cl).\left(\mathrm{Cl}^{-}\right).(Cl). How do gills promote rapid gas exchange by having a thin barrier between water and blood? One-to-one online tuition can be a great way to brush up on your Biology knowledge. [8] The use of sac-like lungs to remove oxygen from water would not be efficient enough to sustain life. A number of fish have evolved so-called accessory breathing organs that extract oxygen from the air. By using the pumping action of mouth and opercular cover, the aquatic animals move water over the gills. [15], Lampreys and hagfish do not have gill slits as such. About 80% of the dissolved oxygen is extracted from the water. Facultative air breathers, such as the catfish Hypostomus plecostomus, only breathe air if they need to and can otherwise rely on their gills for oxygen. The structures that aquatic animals use for gaseous exchange, absorbing oxygen (for respiration) from the water, excreting carbon dioxide (from respiration) into the water Gaseous exchange structures need to: have a large surface area maintain a steep concentration gradient have a copious blood supply Organisms Respond to Changes in their Environments (A Level only), 6.1.9 Investigating Touch and Temperature Receptors, 6.1.12 Investigating Variables that Affect Heart Rate, 6.2.6 Maths Skill: Calculating Maximum Impulse Frequency, 6.2.8 Transmission Across a Cholinergic Synapse, 6.3.3 Examining Skeletal Muscle Under a Microscope, 6.4.6 Control of Blood Glucose Concentration, 6.4.8 Calculating the Concentration of Glucose in Urine, 7. What is rotational grazing, and how does it mimic natural processes? (b) What If? ), Keys to the Trematoda, Vol. A natural history of skin and gill parasites of fishes. Dordrecht: Springer. Predicting the Premier League Top 4: Who are the Favorites? [9][10], In bony fish, the gills lie in a branchial chamber covered by a bony operculum (branchia is an Ancient Greek word for gills). To regain the water, marine fishes drink large amounts of sea water while simultaneously expend energy to excrete salt through the Na+/K+-ATPase ionocytes (formerly known as mitochondrion-rich cells and chloride cells). The water flow through the fish's mouth as well as the blood in gill capillaries follow the countercurrent principle. From 0 - 0.3 secs; 2 Mouth closes and floor raised/ mouth cavity contracts; We also use third-party cookies that help us analyze and understand how you use this website. Which part is directly involved in gas exchange in plant? Examples of air-breathing fish include the mudskipper, lungfish, bowfin, and gar. Why are elastic Fibres important in gas exchange? By far the commonest cause of impaired gas exchange in patients with lung disease is ventilation-perfusion inequality. Construction Project Management 2023 Tips tools best practices to know, Understanding Art of Bluffing. [21] Various protists and Myxosporea are also parasitic on gills, where they form cysts. Image showing the structure of a leaf from a dicotyledonous plant. Heart decompensation. The gills push the oxygen-poor water out through openings in the sides of the pharynx. short diffusion pathway/distance/large SA:V ratio; Mackerel are fast swimming fish whereas toadfish only swim slowly. How do gills promote rapid gas exchange by having a large surface area? When the mouth closes, the gill cover opens and this forces the water into the gill chamber. The breathing cycle is important for maintaining the pressure differential across the gills. The small round alveoli allow for an amazingly large surface area for this gas exchange to take place. Many fishes like shark breathe by pumping at low speed and change to ram ventilation at high speed. (2). Describe the relationships between gill surface area, mass and swimming speed shown in the diagram. London: CAB International and The Natural History Museum. But instead of lungs, they use gills. In your lungs, the main airways (bronchi) branch off into smaller and smaller passageways the smallest, called bronchioles, lead to tiny air sacs (alveoli). What happens when alveoli lose their elasticity? The fish opens its mouth to let water in, then closes its mouth and forces the water through the gills and out through the operculum (gill cover). After this the blood can pick up no more oxygen from the water because there is no more concentration gradient. (3), large numbers of lamellae so large SA; It does not store any personal data. Gills in fish Exchange of gases in fish is very efficient because of: the large surface area of the gills. The high surface area is crucial to the gas exchange of aquatic organisms as water contains only a small fraction of the dissolved oxygen that air does. The large muscles of the body actually do most of the work, but the fins help with balance and turning. The water moves through the mouth over the branched gills. For the continuous flow of water, the pressure in the opercular cavity is always slightly lower than the pressure in the buccal cavity. However, the fish needs to be swimming, which is energetically costly, and its body position with the mouth open may increase drag on the fish and increase the cost of locomotion. The fish opens its mouth to let water in, then closes its mouth and forces the water through the gills and out through the operculum (gill cover). Have a Free Meeting with one of our hand picked tutors from the UK's top universities. The two common mechanical devices used in order to increase the flow of water over the gills surface are explained below: Through the movement of gills as observed in small organisms such that aquatic insect larvae. Summary. Each gill is supported by a cartilaginous or bony gill arch. This is important because there isn't much oxygen in the water, and fish need to absorb enough oxygen to survive. The concentration of oxygen in water is lower than air and it diffuses more slowly. Teleost fish use a buccal-opercular pump to ventilate the gills. Fish gills are organs that allow fish to breathe underwater. [5] The gills of vertebrates typically develop in the walls of the pharynx, along a series of gill slits opening to the exterior. the large surface area of the blood capillaries in each gill filament. The blood vessels are in very close proximity to the lamellae, allowing a short diffusion pathway. Effective exchange surfaces in organisms have: The maximum distance that oxygen molecules would have to diffuse to reach the centre of a, Diffusion is an efficient exchange mechanism for, Insects have evolved a breathing system that delivers oxygen directly to all the organs and tissues of their bodies, The tracheae walls have reinforcement that keeps them open as the air pressure inside them fluctuates, A large number of tracheoles run between cells and into the, For smaller insects, this system provides sufficient oxygen via diffusion. Explain how a fish is adapted for gas exchange? Fish maintains water flow over the gills by holding their mouth open relying on continual movement to ventilate. lamellae thin so short (diffusion) pathway to blood/capillaries; Fish do not have lungs like terrestrial animals do. In some species cutaneous respiration accounts for 5 to 40 percent of the total respiration, depending on temperature. One of the ways in which gas exchange is carried out efficiently is by the countercurrent flow principle. Fish breathing Adaptations for Gas Exchange Mouth & Opercula Alternate opening of the mouth and two flaps of skin that cover the gills called the opercula (singular: operculum) helps to force water across the gill surface = ventilate the gas exchange surface. During gas exchange oxygen moves from the lungs to the bloodstream. Fish have gills that extract or take oxygen out of the water. Patients who have increased physiological dead space (eg, emphysema) will have decreased effective ventilation. Labyrinth fish (such as gouramis and bettas) have a labyrinth organ above the gills that performs this function. The concentration of dissolved oxygen in water is higher than than the blood of the fish. Also co. However, recent studies on gill formation of the little skate (Leucoraja erinacea) has shown potential evidence supporting the claim that gills from all current fish species have in fact evolved from a common ancestor. The gas exchange organs of fish are called gills. The gills' large surface area tends to create a problem for fish that seek to regulate the osmolarity of their internal fluids. Warms air to match your body temperature and moisturizes it to the humidity level your body needs. "[8], Higher vertebrates do not develop gills, the gill arches form during fetal development, and lay the basis of essential structures such as jaws, the thyroid gland, the larynx, the columella (corresponding to the stapes in mammals) and in mammals the malleus and incus. Gas exchange is really important so that we take oxygen for aerobic respiration and get rid of the carbon dioxide so that it doesnt accumulate inside of us. Toadfish 35 8 What causes this pressure difference? Pozdnyakov, S. E. & Gibson, D. I. In this video, Head of Biology Mr May carries out a fish head dissection and explains how the gills of a fish are adapted for efficient gas exchange. The gill filaments have many protrusions calledgill lamellae. The difference in pressure across membranes. Kearn, G. C. (2004). You have two lungs, but they arent the same size the way your eyes or nostrils are. The cookies is used to store the user consent for the cookies in the category "Necessary". (2). He also shares personal stories and insights from his own journey as a scientist and researcher. They also contain elastic fibres which expand to allow air in and recoil to help force out air. the short distance required for diffusion - the outer layer of the gill filaments and the capillary walls are just one cell thick. The gill filaments have many protrusions called gill lamellae. These cookies help provide information on metrics the number of visitors, bounce rate, traffic source, etc. This is easily exemplified (and an acceptable form of explanation in an exam) by a number table. Therefore, even when the blood is highly saturated, having flowed past most of the length of the lamellae, there is still a concentration gradient and it can continue to absorb oxygen from the water. A room has dimensions 3.00m3.00 \mathrm{~m}3.00m (height) 3.70m4.30m\times 3.70 \mathrm{~m} \times 4.30 \mathrm{~m}3.70m4.30m. A fly starting at one corner flies around, ending up at the diagonally opposite corner. 3 Tips for Beginner Players. P111.21atm721torr5.51atmV11.58L141mL0.879LT112.2C135K22.1CP21.54atm801torrV2152mL1.05LT232.3C38.3C, Circle the BEST answer. As the blood flows in the opposite direction to the water, it always flows next to water that has given up less of its oxygen. Their alveolar sacs have a high residual volume, which in turn causes difficulty in exhaling the excess air out of the lung, and patients develop shortness of breath. This is important for fish becaus of the low oxygen concentration in water. Performance cookies are used to understand and analyze the key performance indexes of the website which helps in delivering a better user experience for the visitors.

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