Biology Adaptations 2.5Tim Armstrong
Introduction
In this assignment I will be discussing how adaptations enable gas exchange in specific habitats for a mammal, fish and insect. The specific animals I am studying are Desert Kangaroo Rats, Migratory Locusts and Southern Bluefin Tuna. I will also compare the gas exchange systems, adaptations and identify limitations and advantages of each system.
Mammal
Desert Kangaroo Rat
Dipodomys deserti
Desert Kangaroo Rats are found in North America and live in dry areas with low rainfall and humidity. They live on sandy and rocky, open areas where they eat grass seeds, stems and fruit. Kangaroo Rats gain water needed for gas exchange though their food. Predators to the desert kangaroo Rat are coyotes, foxes, badgers and snakes. The arid conditions that Kangaroo Rats face presents an issue as water is needed for gas exchange to provide a moist surface area for the diffusion of oxygen and carbon dioxide and as there is no open water in most of their habitat they live in. Kangaroo Rats have unique adaptations to prevent water loss which enable them to survive.
Moisture
Desert Kangaroo Rats live in deserts with arid conditions for animals. Desert Kangaroo Rats need moisture for respiration and this moisture is retained within Kangaroo Rats through nasal passage physical adaptations which reduce water loss from respiration. Desert Kangaroo Rats have a form of countercurrent exchange of inhalation and exhalation in their nasal passage in which expired, moist air from respiration is cooled and the water vapor condenses before returning to the body via osmosis into the blood. This adaptation allows for very little water loss and energy loss that would usually occur from respiration. This adaptation allowed Desert Kangaroo Rats to maintain moisture and enables them to gas exchange by allowing oxygen and carbon dioxide to diffuse through this water. This adaptation is important because they rate of evaporation in the Californian Desert (where Desert Kangaroo Rats are most common) is 150 inches per year while their is only 2 inches of precipitation a year. This adaptation allows such efficient water conservation and gas exchange that Desert Kangaroo Rats never need to drink water as long as they have food in which they can get water from oxidization. This adaptation that minimises water loss is so efficient that Desert Kangaroo Rats have similar levels of water content to other animals that are in environment with large amounts of water. Without this nasal passage adaptation, Desert Kangaroo Rats would not be able to conserve enough water needed for gas exchange and would die out as a consequence in their natural habitat.
Desert Kangaroo Rats also have other adaptations which minimise water loss. Desert Kangaroo Rat’s kidneys can concentrate urine up to five times more than human urine resulting in less water being wasted. This adaptation is enabled by a lengthen loop of Henle in Desert Kangaroo Rats. Desert Kangaroo Rats also do not have sweat glands and don’t pant like other mammals to cool down. These two physical and behavioural adaptations minimise water loss in the desert furthermore resulting in retaining enough moisture to carry out gas exchange. In the desert, arid conditions make water valuable. Kangaroo Rats survive in their habitat because they don’t use waste much water.
Lungs
The adaptation of the lungs in Desert kangaroo Rats enables them to carry out gas exchange in their habitat. When Kangaroo Rats breathe in air, the air is pumped through bronchus into the lungs where it goes into the alveoli. The capillary network which surrounds the alveoli then diffuses oxygen via water through the thin cell wall into the blood and gas exchange takes place. The blood from the capillary network is then pumped through the heart and around the body to the cells where they are given the oxygen from the blood and carbon dioxide is exchanged after the conversion of oxygen and glucose into energy. This carbon dioxide is then pumped back around the body into the lungs where it diffuses into the air and is pushed out due to pressure and vacuum provided by the diaphragm. Kangaroo Rats need a gas exchange system to survive in the desert. They use lungs because their environment lacks water and therefore cannot use gills yet they are too big for trachea air delivery system as there would be to much dead air inside the Kangaroo Rat and the trachea may not be able to support the weight of large animal (explanation of these ideas in discussion).
Surface Area
Alveoli adaptations create the large surface area needed for gas exchange in Desert Kangaroo Rats. Surface area in the lungs is increased by alveoli which are effectively small balloons with gas exchange surfaces within them. Alveoli increase surface area by splitting the lungs up into many small pockets which inflate when air is inhaled. Alveoli have a large surface area to volume ratio which is more efficient than if the lungs only had one flat gas exchange surface surrounding the lung. Large capillary networks cover the alveoli and helps large volumes of gases to exchange. The blood goes through the capillary network and carbon dioxide and oxygen diffuse over the cell wall. Without this increased surface area adaptation the Kangaroo Rat would not get enough oxygen and energy to power life processes resulting in them dying.
Concentration Gradient
The Desert Kangaroo Rat has a diaphragm and sealed lung adaptation which improves their concentration gradient for diffusion. The lung is sealed which creates a vacuum where there is only one exit and entrance for air. When the diaphragm contracts downwards more volume is created in the lungs and there is a lower pressure resulting in higher pressure air from outside coming into the lungs. The diaphragm adaptation increases the concentration gradient in Kangaroo Rats and this results in faster diffusion as opposed to passive diffusion of air into the body. The diaphragm increases the concentration gradient by sucking fresh air into the lungs that has a high concentration of oxygen (than the expired air) which better diffuses with the low oxygen blood. This adaptation allow Desert Kangaroo Rats to survive in their environment as they can pull in more air to diffuse oxygen from which is more efficient than passive diffusion of air into lungs. If the Desert Kangaroo Rat were to not get enough air, resulting in less oxygen being diffused into the body then the Kangaroo Rat would not have enough energy for life processes and would not survive.
Diffusion Distance
The cell wall between the alveoli and the blood is adapted to be very thin to allow gases to diffuse easily. The cell wall is from (0.5 - 2 microns thick) which enables the shortest possible diffusion distance.
Insect
Migratory Locust
Locusta migratoria
Migratory Locusts live in Asia, Africa, Australia and New Zealand. Migratory Locusts can inhabit many regions as they move such as plains, deserts and seashores. They like to feed on wheat plants and sugar cane as well as other forms of vegetation along routes they migrate. They move in swarms of millions of locusts and can eat as much as their entire body weight in a single day. Birds, snakes and lizards prey on migratory locusts however the impact of these predators is minimal. Fungi and bacteria as well as mites eat locusts eggs which has a big impact as the lifespan of locusts is less than one month. Locusts can only survive for a short period of time in dry conditions.
Basic overview of gas exchange in migratory locusts
Air is pumped through holes in the insect by muscular contractions and expansions of the abdomen. The oxygen in this air is delivered directly to the cells through the trachea network in the insect and at the end of this trachea is a moist area with water where gas exchange diffusion takes place. Oxygen from the air diffuses into the cell and carbon dioxide from respiration is diffused out of the cell into the air in the trachea and eventually leaves the insect.
One physiological adaptation of Migratory Locusts that helps them to carry out gas exchange is the spiracles they have on the surface of their bodies. Chemoreceptors detect the amount of oxygen and carbon dioxide in the body if there is high CO2 and Low O2 they open up allowing oxygen to enter the trachea of the insect. This opening and closing of the spiracles prevents water loss enabling the ability to have a moist environment for gas exchange. This moist environment allows the gases to diffuse through the cell wall using the water. Without this adaptation, Migratory Locusts may dry up in flight and might not have enough water for gas exchange and therefore die.
Another adaptation in Migratory Locusts which helps gas exchange is the muscular expansions and contractions of the abdomen which pumps air into the trachea for gas exchange. This adaptation enables efficient gas exchange by creating a high concentration gradient. These contractions and expansions of the abdomen creates differences in pressure between the inside and the outside and this change in pressure create air movement as the air moves from areas of high pressure to low pressure areas. Such contractions allow the insect to push out expired carbon dioxide, a product of respiration, and pull in fresh oxygen. This aids gas exchange because it allows a higher amount of oxygen to come in contact with the cells as the new oxygen is constantly coming in. The alternative is passive diffusion of air through the trachea which is much slower and would not suit the insects habitat and lifestyle where they are consistently flying and need maximum amount of oxygen.
Network of Trachea in Migratory Locusts
Migratory Locusts use a network of trachea throughout the insect to deliver oxygen directly to cells for gas exchange and also remove carbon dioxide from the body. This is efficient because it does not require a respiratory pigment such as hemoglobin to carry oxygen which slows the gas exchange process. The trachea gas transport system is much more efficient as it allow a high rate of oxygen flow.
The trachea tubes enable a large surface area:volume ratio as the larger branches of tracheae break into smaller branches of tracheoles creating more surface area for diffusion of gases into cells. As well as this, during exercise the insect releases more water near the ends of the tracheoles where diffusion is taking places which increases surface area and moisture and allows oxygen to be diffused and converted into energy faster.
Migratory Locusts have a ring like adaptation on their trachea which maintain the structural stability of the air passage way. These rings provide structural integrity (can be seen in the image to the side) and enable the tubes to always be round and open instead of collapsing under the weight of the insects body. Without this adaptation, air would not be transported to the cells as the trachea would collapse under the weight of the insect.
Fish
Southern Bluefin Tuna
Thunnus maccoyii
Southern bluefin Tuna live in the southern hemisphere and are a fast swimming fish which can become quite large as an adult Tuna. Bluefin Tuna feed on a variety of fish and crustaceans including sardines, mackerel and eels. Their predators include orcas and sharks. Southern Bluefin Tuna are also over fished due to their high value as a food. Bluefin have two different muscles for swimming, one for short distance speed and another for long distance swimming as they migrate.
Brief description of gas exchange in Tuna
Water from the sea enters the mouth and flows over the gills, gill filaments and gill lamellae. Blood flows through the gills in the opposite direction of the water and diffusion takes place as the low oxygen, high carbon dioxide blood diffuses with the high oxygen, low carbon dioxide water. This blood is then circulated around the body and is delivered to cells where respiration occurs. The blood is pumped back to the gills where is diffuses with the water and the process repeats.
Surface Area
Southern Bluefin Tuna have a structural adaptation called gills which helps efficient gas exchange in reduced oxygen environments (when compared to air). Gill arcs in the mouth hold rows of thin gill filaments which are separated from each other. Additionally, gill filaments have rows of gill lamellae (see image) within them. This splitting of gas exchange surfaces creates more surface area than if it were just a flat surface. This increased surface area (more places for diffusion to take place) allows more rapid oxygen and carbon dioxide diffusion resulting in more oxygen being gained. Tuna are fast swimming fish that need to be fast to catch their food. This adaptation increases the potential rate of gas exchange making gas exchange more rapid so they have enough energy to hunt.
Concentration Gradient
In addition to gills, Southern Bluefin Tuna also have an adaptation which enables countercurrent flow between blood and water over the gills improving the efficiency of gas exchange. As the water with high oxygen content flows over the gill lamellae, blood with low oxygen flows in the opposite direction. Countercurrent is efficient because the gas concentrations do not meet equilibrium as as such there is always a difference in the concentration gradient and so gases continue diffusing longer than in concurrent systems.
When the blood has diffused a decent portion of oxygen from the water and it is just about to leave the gills it meets fresh water which has 100% oxygen content and as the water is has 90% oxygen content, there is still a diffusion difference and diffusion continues to take place all the way along. Countercurrent flow is more efficient than concurrent flow because the blood and the water never meet equilibrium (50% oxygen in blood and water) and instead could theoretically reach 100% oxygen diffusion from the water if the gill was long enough.
These physical adaptations which increase surface area and enable countercurrent flow increase the amount of oxygen that can be extracted from the water. This helps Southern Bluefin Tuna to carry out gas exchange more efficiently which is important because the habitat for Tuna is water. In water there is less than 1% oxygen available to animals compared to 21% in air so Tuna need to be more efficient about extracting it from water and countercurrent flow achieves this. Tuna are also very fast swimming fish when hunting and need more oxygen than slower swimming fish.
Short Diffusion Distance
Southern Bluefin Tuna additionally have a very thin gill lamellae which are only 5µm thick resulting in a short diffusion distance which allows easy gas exchange between the cells as the oxygen goes into the cell and carbon dioxide is removed from the cells. This once again increases how rapid gas exchange can take place increasing the amount of oxygen which can be used in energy conversion.
Discussion
Southern Bluefin Tuna and Desert Kangaroo Rats both have the same demand, extraction oxygen and removing carbon dioxide. However, their habitats and environments are very different and they complete gas exchange in different ways. Tuna must have adapted a more efficient gas exchange system than Kangaroo Rats as the amount of oxygen in water is less than 1% while in air it is 21%. Southern Bluefin Tuna achieve this efficiency with adaptations that maximise surface area and enable countercurrent flow of blood and water. Gill lamellae maximise surface area so Tuna can get enough oxygen during fast paced swimming and countercurrent flow maximises the amount of oxygen that can be extracted from the blood. This is more efficient than Kangaroo Rats because Kangaroo Rats have concurrent flow which means they eventually reach equilibrium after only extracting 50% oxygen from blood and only releasing 50% carbon dioxide from blood. This contrasts to Tuna where they can theoretically extract 100% of the oxygen from the water. This efficiency allows Southern Bluefin Tuna to live in habitats with much lower levels of oxygen.
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. Kangaroo Rats 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 Tuna having gills is that as long as the Tuna is submerged in water they will always have enough water for the moisture factor in gas exchange. This contrasts to Kangaroo Rats and Migratory Locusts where they need moisture preserving adaptations to survive in their habitat. Kangaroo Rats use countercurrent condensing of expired air into water vapour to retain water and migratory locust have spiracles which open and close to prevent water loss.
Southern Bluefin Tuna and Desert Kangaroo Rats use blood to transport oxygen around the body whereas Migratory Locusts use networks of trachea to deliver oxygen directly to the cells. There are advantages and limitation to both method of oxygen transport systems. The trachea system has the advantage of directly oxygen delivery to cells without the need for a respiratory pigment which makes it more efficient. The issue with this system is that it does not work on larger animals as the trachea could not support the weight of the body if it were the size of a Kangaroo Rat and the trachea would collapse in on itself denying oxygen to cells. Even though migratory locusts have the rings adaptation which provide structural integrity, it would still not be able to support more weight than an insect.
Another disadvantage of trachea is the dead air inside the insect it creates. Dead air is the expired air inside the insect that is not fully pumped out by muscular contractions as insects cannot pump out all the air inside them. This air is a limitation because as it is already expired it cannot be used for respiration and is instead taking up space for air that could have oxygen. Lungs also have this limitation while gills don’t as they don’t use air and the water can continuously flow.
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