Biology
2.5 Gas Exchange
Introduction
In this assignment I will discuss adaptations relating to gas exchange in Llamas, Swordfish and Hummingbirds and will use Fick's law to relate gas exchange adaptations to the rate of gas exchange.
Ficks Law and Gas Exchange Factors
The Fick's Law equation states the rate at which gases diffuse. To maximise the efficiency of gas exchange, Q is maximised through various adaptations and in each section I will will discuss how Q is increased. D is the diffusion coefficient, A is the surface area of the membrane, P1 and P2 are the partial pressures of the gases and L is the length of diffusion distance.
Llama
Lama glama
Llamas are long necked mammals that live in the highlands of South America, Argentina and Chile. They migrated from North America during an ice age. Llamas live in high regions with little free standing water and eat vegetation. Diseases and parasites are the greatest threats to Llamas as well as poisonous plants and predators. Llamas often have to run very fast to escape predators.
Gas Exchange in mammals in achieved through the use of lungs. Air is pushed into the lungs through the use of the diaphragm creating negative pressure within the lungs drawing air in. The lungs only have one entry/exit point and air flows from an area of high concentration to an area of low concentration as the diaphragm contracts as as air flows from an area of high pressure to an area of low pressure due to increasing the volume of the chest. Air is then supplied to the many alveoli compartments in the lungs that create larger surface area for diffusion to take place. In the alveoli, carbon dioxide diffuses into the air and oxygen diffuses into the bloodstream before blood is circulated around the body of the Llama.
Llamas have an adaptation of erythrocytes with a high concentration of haemoglobin resulting in them having the highest concentration of hemoglobin in their blood for a mammal which enables them to survive in their high altitude habitat in the mountains. Haemoglobin is a protein responsible for carrying oxygen in the blood and when oxygen binds with hemoglobin it becomes oxyhemoglobin which is then distributed to cells. This increased hemoglobin help enable maximum oxygen absorption which is important at high altitudes because while the air has the same amount of oxygen, the atmospheric pressure is much lower resulting in lower partial pressure. This “thin” air makes it harder to breathe as there is less pressure on the oxygen molecules and there is more empty space between the molecules of breathable air. Lower air pressure at high altitude also means that less air is drawn into the lungs by the diaphragm than at low altitude as the difference between the outside pressure (which is now lower as less pressure) and inside pressure (which is low but stays the same) is lower. High altitude also results in lower pressure for diffusion and the oxygen diffuses more slowly but as blood moves at the same rate the blood becomes more oxygen deprived. Furthermore, at the high altitudes that Llamas inhabit the haemoglobin in the blood has a lower affinity for the oxygen resulting in less oxygen absorption. Because Llamas have high levels of haemoglobin due to the erythrocytes adaptation they can still absorb a lot of oxygen from the blood and can function normally where other mammals would not have enough hemoglobin to carry enough gas exchange. Increased hemoglobin concentration in blood maximised the partial pressure difference which in turn increases the rate of gas exchange in Fick’s law.
Also, llamas are able to travel long distances without water due to an adaptation in their stomach. They have 3 stomach compartments and they chew their cud. Cud is a mouthful of swallowed food that is regurgitated from the first stomach. This enables llamas to carry out gas exchange by ensuring there is always moisture on the gas exchange surfaces so diffusion can take place. The Llama lives in high altitude environments with often little freestanding water and gets a lot of this moisture from eating vegetation. It is essential that the Llama be able to retain this moisture as otherwise the gas exchange surfaces would not be moist and carbon dioxide and oxygen could not diffuse into the blood as easily as over water. Llamas would not be able to complete gas exchange as there is little water in their habitat and they would not survive.
Increased lung capacity in Llama is another adaptation which enables them to survive in their habitat as they need to outrun their predators. Increased lung capacity increases the surface area as there are more avioli in this volume than if it were smaller. This increases gas exchange surface area is important because it helps satisfy the surface area component of Fick’s Law. By increasing surface area more oxygen can be diffused into the blood at a more rapid rate and this is then converted to energy which enables Llama to outrun their predators and survive in their habitat. Q is maximised by increasing the surface area.
Hummingbirds
Trochilidae
Hummingbird preparing to “hover” while it feeds.
Hummingbirds are small birds that make an audible sound due to the fast oscillating of their wings of about 80 times per second. Hummingbirds eat nectar, tree sap and polin. They are found in north America and their primary threat is loss of habitat.
Gas Exchange in birds is achieved through the use of air sacs that receive air from the primary bronchi and deliver gases to gas exchange surfaces in lungs. The relative size of lungs in birds is smaller than that of mammals but the air sacs are connected through a series of tubes which create more volume resulting in volume twice the volume than that of mammals at the same size. Birds have higher energy requirements when resting than all other vertebrates. The oxygen depleted blood now diffuses with the high O2 oxygen and the high carbon dioxide concentration blood diffuses into the air and out the bird though the same passage way. Unlike in mammals, birds don’t expand their lungs but only expand the air sacs inside of them. The air is also exhaled through the contraction of these air sacs and this results in birds having a rigid lung structure constant expanding and contracting.
Hummingbirds have an heart adaptation that enable a faster heart rate which helps them to survive in their habitat as they need a fast rate of gas exchange due to the flapping of wings 80 times per second. The high heart rate helps circulate the blood faster and deliver oxygen faster to organs than in other birds. The blood carries the same amount of oxygen and carbon dioxide, it just goes around the body faster so more can be delivered. This heart rate adaptation is very important for hummingbirds as they need it to carry out gas exchange efficiently. Hummingbirds fly at up to 100km/h and they don’t sit as they get their food, they flap their wings and hover. These increased energy requirements of hummingbirds result in a heart rate that increases from 250 beats per minute when resting to 1250 beats per minute when active. This adaptation is enabled by hummingbird having the largest relative lung size in the animal kingdom. This larger heart size enables faster and more effective pumping of blood for gas exchange.
This adaptation relate to Fick's law as by increasing the partial pressure of the blood more oxygen and carbon dioxide is diffused in and out. This helps maximise the rate of diffusion Q.
Hummingbirds also have an adaptation called torpor which enables them to conserve energy in period of low temperature and limited food. Humming birds naturally have one of the fastest metabolisms but during periods of cold weather and at night when they are not feeding they can go into a hibernation like state called hypothermic torpor which slows their heatbeat. Hummingbird body temperature drops from 40 degrees celsius to 20 degrees celsius during torpor. In addition to this, wingbeat frequency also changes to a more slow movement to conserve energy. This behavioural and physiological adaptation is important because the fast heart rate is important for gas exchange during the day in which increased the partial pressure in the blood increases the rate of gas exchange but a night when not searching for food or in nonoptimal conditions, the humming bird would waste significant energy on gas exchange and would not be able to survive at its normal heart beat when resting for long periods. Even though this adaptation slows gas exchange by lowering the heartbeat, it makes sure the hummingbird conserves enough energy to survive the night and then carry out gas exchange in its normal fashion the next day.
Hummingbird in torpor state
Swordfish
Xiphias gladius
Swordfish are fast swimming fish that are commonly found in the Pacific, Atlantic, and Indian oceans and can reach speeds of up 65km/h weighing up to 650 kg. The swordfish’s predators are orca whales, marlins and sailfishes.
In fish water enters through the mouth goes over the gills where gas exchange takes place. The water flows over lamellae which aids gas exchange by providing a bigger surface area. Carbon Dioxide in the blood diffuses out into the water and fresh oxygen in the water diffuses into the bloodstream. This blood is then pumped around the body where oxygen is delivered to the cells and is exchanged with carbon dioxide as a product of respiration. This carbon dioxide diffuses out into the water and the process is repeated again.
For swordfish to carry out gas exchange there needs to be large surface area, moisture, short diffusion distance and a high concentration gradient. Swordfish have a structural adaptation called gills which enable a large surface area for gases to diffuse across. Increased surface area is enabled by the splitting up of gills into, gill arches, gill filaments and gill secondary lamellae. This has more surface area because instead of a flat surface, the gill is broken up into a 3D shape with surface area on more than 2 sides.
Gill arches hold two rows of gill filament, which have secondary gill lamellae on them further increasing surface area. The repeated splitting of gas exchange surfaces in gills enables a large amount of surface area to be created in the same space which creates a large surface area:volume ratio. Larger surface area is important in gas exchange because it means more areas where gas exchange can occur and diffusion of oxygen and carbon dioxide can occur which increases the rate of diffusion.
The moisture component of gas exchange is met because the fish are constantly in water but the medium is also very efficient because unlike in lungs, oxygen does not have to be transferred to another substance to diffuse. The short diffusion distance is maintained by gill secondary lamellae adaptation which makes them very thin. A short diffusion distance is important because it makes gas exchange faster as it takes less time to diffuse.
A high concentration gradient created by an adaptation in the gill secondary lamellae which enables countercurrent flow of blood and water increases the amount of oxygen that can be diffused into the blood in increases the amount of carbon dioxide that leaves the bloodstream.
Countercurrent flow creates a high concentration gradient by making sure there is always a diffusion difference between the substances so diffusion never meets equilibrium. In concurrent flow substances diffuse until there is the same on both sides of the cell. This means that by the end of diffusion on a concurrent flow surface both the blood and the water have 50% oxygen and 50% carbon dioxide. Countercurrent flow of water and blood is more efficient and results in almost all oxygen (near 100%) being diffused into the bloodstream. Initially the blood has a lot of CO2 as a product of respiration and going around the body. This high concentration CO2 blood meets lower concentration CO2 water and starts to diffuse. As the blood flows through the secondary lamellae it meets more fresh water which has just come in and has an even higher carbon dioxide content than the water before it so even more co2 diffuses. talk about oxygen.
High concentration gradient is important because it extracts large amounts of oxygen from the water and diffuses a large amount of co2 without needing more surface area.
Adaptations such as gills and countercurrent flow in gill lamellae enable gas exchange and allow Swordfish to survive. The oxygen content in water is around 1% compared with 21% in air so gas exchange needs to be more efficient to extract the same amount of energy and these adaptations enable this. Furthermore, Swordfish are extremely fast swimming fish and so they need to get maximum oxygen so they have enough energy to swim fast. As they increase speed more water will pass over their gills increasing the rate of diffusion and increasing the amount of oxygen let in.
Discussion
Swordfish and Llamas both have the same demand, extraction of oxygen and removing carbon dioxide. However, their habitats of water and high altitude environments are very different and they complete gas exchange in different ways. Swordfish must have adapted an efficient gas exchange system as the amount of oxygen in water is less than 1% while in air it is 21%. Swordfish achieve this efficiency with adaptations that maximise surface area and enable countercurrent flow of blood and water. Gill lamellae maximise surface area so swordfish can get enough oxygen during fast paced swimming and countercurrent flow maximises the amount of oxygen that can be extracted from the blood. This contrasts to Llamas as even though there is 21% oxygen in air, the partial pressure of air at high altitude means less air is pulled in and so Llamas must have their own adaptation to increase the concentration of hemoglobin in red blood cells. Gas exchange is still more efficient in Swordfish because they have countercurrent flow where they can extract up to 100% of the oxygen from the water while Llamas reacher concentration gradient equilibrium much faster resulting less less efficient gas exchange for relative size. Swordfish also use water as a medium for gas exchange just like Llamas but as they live in water they don’t need to diffuse the gases into a liquid substance before gas exchange takes place into the bloodstream.
Countercurrent flow in gills may be more efficient but a limitation of gills is that they must be in water to work properly. Water gives gills, gill filaments and gill lamellae buoyancy and separates them allowing more rapid gas exchange as there is more surface area. Without water, the gills collapse and do not function properly and the fish die. Llama lungs have the opposite limitation as they cannot breathe underwater as they are not designed to extract oxygen from water like fish gills are.
An advantage swordfish having gills is that as long as the fish is submerged in water they will always have enough water for the moisture factor in gas exchange. This contrasts to Llamas where they need moisture preserving adaptations to survive in their habitat as their habitat has little freestanding water and they gain a lot of moisture from vegetation.
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