Receptor

Receptor Definition

A receptor is a protein which binds to a specific molecule. The molecule it binds is known as the ligand. A ligand may be any molecule, from inorganic minerals to organism-created proteins, hormones, and neurotransmitters. The ligand binds to the ligand-binding site on the receptor protein. When this binding happens, the receptor undergoes a conformational change. This change is shape slightly alters the protein’s function. From this, a number of things can happen. The conformational change in the receptor can cause the receptor to become an enzyme and actively combine or separate certain molecules.

The change can also cause a series of changes in related proteins, eventually transferring some sort of message to the cell. This message could be a metabolic regulation message, or it could be a sensory signal. The receptor has a certain capacity to hold onto the ligand, known as the binding affinity. Once this attraction wears out, the receptor will release the ligand, undergo a change to the original shape, and the message or signal will end. The speed of this turnover depends on the strength of the affinity between receptor and ligand.

Other molecules can also attach to the ligand-binding site on a receptor. These are called agonist molecules if they mimic the effect of the natural ligand. Many drugs, both prescription and illegal, are synthetic agonists to molecules like endorphins, which create feelings of satisfaction. However, these molecules often have a stronger affinity for the receptor than the natural ligand does. This means the agonist will stay attached to the receptor longer, which is why tolerances develop to certain drugs and painkillers. To get the same number of nerves firing when so many are already blocked by the drug requires a much higher dosage.

Still other molecules can act like antagonists, or molecules which block the ligand binding site on the receptor but do not allow the receptor to undergo a conformation change. This blocks a signal entirely. Some receptor antagonists include drugs which are used to wean people off of heroin and alcohol dependency. These act by making the use of the drug no longer pleasurable. Other antagonists include certain proteins in snake venom which mimic platelet binding proteins. The receptors which would normally connect platelets and prevent bleeding are therefore disabled. This can lead to internal bleeding and death. Pharmaceutical companies are interested in both agonists and antagonists for their potential to create effective medicines.

Types of Receptors

There are literally thousands of different types of receptors in the mammalian body. While there are far too many to start listing out, receptors do fall into some very broad categories of function. Many are used in “cellular signaling”, which is an enormously complex system of signals and responses mediated almost entirely by receptors and the ligands they receive. These include receptor proteins embedded in the cellular membrane which activate other sequences upon receiving a ligand, and the receptors found in the immune system which are structured to find intruding proteins and molecules. Below is the general model for cell signaling, which can take many different forms.

Another type of receptor is the gated ion channel, which opens a special passage upon the attachment of a ligand and allows ions to flow freely across the membrane. Because of this action, the electrical voltage which is maintained across the membrane is lost, and the region becomes depolarized. When large areas of cells like neurons are depolarized, an action potential is generated. This travels down the nerve as an electrical signal. At the end of the neuron, neurotransmitters are released, which act as ligands on the receptors of the next nerve cell. In this way, the signal travels quickly throughout the body and is based on the action and reversibility of receptor proteins.

Still other receptors have a high affinity for their ligand, and are used in functions such as binding the cell to the extracellular membrane and other cells. These receptor proteins still change shape when their ligand is bound, signaling to the cell that it is in contact with other cells. Different organisms use this in different ways. Multi-cellular animals use this to orient their cells and ensure the connections between them. Single-celled organisms may use these receptors to signal a defense mechanism or other action when space becomes too crowded. Many receptor proteins are ubiquitous among animals, as they have been conserved throughout evolution due to their extreme usefulness.

Examples of a Receptor

The Insulin Response

Insulin is an extremely important hormone which helps regulate the amount of glucose in the blood. Glucose is the main fuel for cells, but it needs a special transport molecule, Glut4, to help it enter the cell. Observe the image below.

As blood glucose levels increase, special receptors in the pancreas sense this, and begin producing and releasing insulin into the blood stream. Nearly all cells in the body have insulin receptor proteins. When these receptor proteins contact insulin, it binds to the ligand-binding location on the receptor protein. This causes a conformational change in the protein. This change in the receptor sets off a series of other reactions triggered by associated proteins. These proteins create a messenger molecule which affects the movement of Glut4 to the cell membrane. While insulin is present, this happens quickly. The vesicles holding Glut4 fuse to the membrane, bind glucose, and transport it into the cell. When insulin disappears, this stops insulin production and shuts off uptake of glucose. Not only is the insulin receptor protein involved, but a number of other receptors used in associated reactions and other cells. As can be seen, the role of a receptor can become quite complicated.

Taste Response

A different type of receptor can be seen in the example of a taste nerve. Parts of the nerve project into the mucous membrane of the mouth. As sugar, salt, or other molecules are eaten, they dissolve into the saliva and are distributed throughout the mucous membrane. Each of these ligands has different cells containing receptors specific to it. These receptors are gated ion channels, like in a nerve cell. When a ligand attaches to them, they allow ions to pass through the membrane. This causes an area of the membrane to depolarize. If there is enough ligand molecules, many receptors will be activated at one, causing an action potential.

This wave of depolarization will move down the nerve cell until it reaches the other side. Once there, special capsules containing neurotransmitters are burst by the action potential, releasing the ligands into the space between nerves. The receptors and the next nerve receive the ligand, and the process starts over. This happens several times between the tongue and the brain. The signal finally reaches processing centers in the brain, and the “sweet” taste is comprehended. This all happens in fractions of a second.

Quiz

1. Which of the following is a receptor?
A. A protein which lowers the activation energy of a reaction if a substrate is present
B. A protein which accepts a ligand, causing a sequence of other reactions
C. A structural protein which does not bind to other molecules

Answer to Question #1

B is correct. Answers A and C represent other uses of proteins, as not all proteins act as receptors for specific ligands. Answer A is an enzyme, or protein which speeds a particular reaction. Some enzymes can be receptors, but they often have multiple regions which complete the separate tasks.

2. Which of the following is NOT a task of receptors?
A. Receiving a ligand
B. Transferring a signal
C. Storing energy

Answer to Question #2

B is correct. Receptors must receive a ligand to be a receptor, and this action often transfers a signal, message, or molecule the cell needs. Receptor proteins do not store energy themselves, but are often used to activate the energy or storage molecules like ATP and NAHD. This is how many receptors start cascading reactions.

3. A pharmaceutical company is developing a new drug. The drug is an antagonist for pain receptors, and blocks the feeling of pain. The drug works, but the company is concerned that the drug’s affinity for the receptor is too high. Why is this a concern?
A. It is not a concern
B. A high affinity means people will only need to buy one dose
C. The drug may stay attached to the receptor

Answer to Question #3

C is correct. If the drug stays attached to the receptor for too long, the patient may never be able to feel again. Conversely, the blocked up receptors could cause a stronger pain reaction when the receptors do function, requiring an ever-higher dose and causing dependency on the medicine.

References

• Lodish, H., Berk, A., Kaiser, C. A., Krieger, M., Scott, M. P., Bretscher, A., . . . Matsudaira, P. (2008). Molecular Cell Biology (6th ed.). New York: W.H. Freeman and Company.


• Nelson, D. L., & Cox, M. M. (2008). Principles of Biochemistry. New York: W.H. Freeman and Company.


• Widmaier, E. P., Raff, H., & Strang, K. T. (2008). Vander’s Human Physiology: The Mechanisms of Body Function (11th ed.). Boston: McGraw-Hill Higher Education.

Receptor

Ketone Bodies

Ketone Bodies Definition

Ketone bodies, or simply ketones are substances produced by the liver during gluconeogenesis, a process which creates glucose in times of fasting and starvation. There are three ketone bodies produced by the liver. They are acetoacetate, beta-hydroxybutyrate, and acetone. These compounds are used in healthy individuals to provide energy to the cells of the body when glucose is low or absent in the diet.

Above are the three ketone bodies. Acetone (left), acetoacetate (middle), beta-hydroxybutyrate (right).

Why Are Ketone Bodies Formed?

When glucose levels are high in your body, it is busy storing the excess as fats, building proteins, and in general growing. This is known as the absorptive state. When you fast, or are being starved, the glucose levels in your blood quickly decrease. This triggers the body to enter the postabsorptive state. In this state, the body starts converting fat back to fatty acids, glycogen into glucose, and even starts breaking down amino acids for energy.

While glycogen is just a storage product of glucose and can be quickly converted back, only so much glycogen is stored in the body (mainly in the liver). Once these stores are depleted, the body must resort to the other breakdown products for energy. Luckily, most of the cells in the body can survive off of fatty acids, created from the breakdown of fat. This is not true, however, for the brain and liver. The brain cannot receive fatty acids, which cannot pass through the blood-brain barrier. The liver, in order to keep supplying the brain with glucose, must convert amino acids, glycerol, pyruvate, and lactate into glucose. This process is called gluconeogenesis, and also produces the two ketone bodies acetoacetate and beta-hydroxybutyrate. It releases these ketone bodies, along with glucose, into the blood stream to feed the brain. By this point, the muscles and other organs have mainly switched to fatty acids for energy, conserving the glucose for the brain. This is known as glucose sparing, and is very important for animals which must undergo long periods of fasting or starvation.

The brain prefers glucose as a source of energy, but will begin to switch to ketone bodies after about 4 days of starvation. This greatly increases the amount of time an organism can go without food, however it can also begin to cause negative side-effects. If food is not eaten to replenish the glucose supply, ketone bodies can begin to build up. When this happens, acetone is formed from the spontaneous breakdown of the other ketone bodies in the blood. Acetone is a volatile and reactive substance. When it begins to build up in the blood it can lower the pH of the blood, a condition called acidosis. Acidosis affects nearly all bodily tissues, reducing their function and messing with the enzymes of the body, which rely on a specific pH balance. Ketoacidosis, or acidosis caused by excessive ketone bodies, will lead to coma or death if not reversed.

Ketone Bodies in Diabetes

Diabetes is a condition in which the body cannot or will not produce insulin, an important molecule in the glucose cycle. Insulin signals to the cells of the body to uptake the glucose in the blood and use it for energy. In those with diabetes, this signal is not present and without artificial insulin, the glucose will stay trapped in the blood. Not only can the cells of the body not get energy, but glucose also holds the base molecule for many other cellular activities. Without glucose in the cells, the body begins to uptake fatty acids from the blood, to provide the energy.

The lack of glucose also triggers the liver to begin making glucose. As this happens, ketone bodies are release, just as in a regular person. However, a diabetic person has a compounded problem. Ketone bodies can be used for energy, but only if the proper intermediaries are present. These usually come from the breakdown of glucose. But, in a diabetic, very little glucose has been broken down. This means that even the ketone bodies cannot be used for energy. As such, they begin to build up relatively quickly.

This causes a sudden and severe ketoacidosis. Diabetes is often diagnosed by the smell of acetone or fruit on a person’s breath and highly acidic, acetone laden urine. These signs indicate severe ketoacidosis and could be life-threatening. Luckily, a dose of insulin will allow the blood glucose levels to drop, the intermediates required will be created from the breakdown of glucose, and the ketone bodies will be cleared out of the system in a short time.

Ketone Bodies in Dieting and Starvation

Interestingly, some recent fad diets have come under scrutiny for causing ketoacidosis in people who practice them. These diets focus on low carbohydrates and high protein. Because carbohydrates are complex forms of glucose, removing them from the diet effectively removes glucose from the diet. This works for a little while, because the body is required to get the energy it needs from fat. However, consider the case of the diabetic, and think about why this might be a terrible idea.

Without blood glucose, the cells in the body are again required to survive off fatty acids, derived from stored triglycerides. The brain cannot survive off of these fatty acids, and the liver must undergo gluconeogenesis to produce glucose for the brain. While it does this, it also produces ketone bodies. For short periods of time, the body is able to derive its energy this way. But, as the glucose levels get lower and lower, so do the intermediates required to utilize ketone bodies as energy. Eventually, more ketone bodies will be made than can be used, and they start to build up.

Even when a person is still eating on these diets, the complete lack of carbohydrates makes it incredibly hard for the body to keep up, and acidosis begins to occur. Much like in someone with diabetes, the level of acetone in the urine will increase and the breath may smell sweet or like acetone. The creators of these diets often call this a “common dieting problem”, but ketoacidosis is not common in healthy people and forcing your body into that state is dangerous. Above are some of the listed symptoms acidosis may cause. Further, it has been found that an acidosis of the blood can lead to less calcium uptake from the diet and deposition into the bones. This means that not only are you basically starving yourself, you are also weakening your bones.

Quiz

1. Which of the following is a positive effect of ketone bodies?
A. Lowers blood pH
B. Provides cells with energy
C. Can degrade into acetone

Answer to Question #1

B is correct. Ketone bodies are useful molecules for allowing organisms to go long periods without new glucose. Eventually however, they will cause acidosis because of the acetone they create, causing a slew of problems for the organism.

2. Why are ketone bodies created?
A. On accident, as a by-product of creating glucose
B. To lower the blood pH
C. As an energy source for use anytime

Answer to Question #2

A is correct. While ketone bodies are created as a by-product of gluconeogenesis, evolution has found uses for them. Most cells are equipped with the appropriate enzymes to make energy out of them. However, they are not used for energy all the time and the fact that they lower blood pH makes them less desirable for continual use.

3. You are looking into the Bacon Diet, a new fad some of your friends are doing. In this diet, you eat only bacon for all 3 meals, and drink only water in between. Why is this a bad choice?
A. Bad choice? This sounds awesome!
B. The excess protein and lack of carbohydrates will cause ketoacidosis.
C. Bacon is expensive

Answer to Question #3

B is correct. Don’t get me wrong, I love bacon as much as the next guy. But the fact is, your body needs carbohydrates not only for glucose but to supply many of the intermediaries it uses in the breakdown of all foods into energy. Without these, and with so much extra protein, the body will quickly resort to ketone bodies for energy. This can have serious consequences for blood pH and deleterious health effects over time.

References

• Campbell, T. C., & Campbell, T. M. (2006). The China Study. Dallas: Benbella Books.


• Nelson, D. L., & Cox, M. M. (2008). Principles of Biochemistry. New York: W.H. Freeman and Company.


• Widmaier, E. P., Raff, H., & Strang, K. T. (2008). Vander’s Human Physiology: The Mechanisms of Body Function (11th ed.). Boston: McGraw-Hill Higher Education.

Ketone Bodies

Liposome

Liposome Definition

A liposome is a closed, spherical lipid bilayer, which forms an internal cavity capable of carrying aqueous solutions. A lipid bilayer is composed of two sheets of tightly arranged phospholipids. These molecules have a hydrophobic tail and a hydrophilic head region. When two single membranes come together, the hydrophobic tails attract toward each other, while the heads of both membranes are attracted to the surrounding water. This forms a double layer of phospholipid molecules, which exclude the internal solution from the outside. The solution can then be transported with the liposome where it is needed.

A liposome should not be confused with either a micelle or a lysosome. A micelle is similar to a liposome in that it is a sphere of phospholipids. However a micelle is composed of a single layer and therefore does not have an aqueous interior. A lysosome is a specialized organelle in cells which separates caustic enzymes from the interior of the cell. While it too is similar to a liposome, it has many specialized proteins embedded in its membrane which help it function as an organelle within the cell.

How Does a Liposome Form?

Liposome can be generated naturally when tissues are disturbed. When tissue is damaged, small pieces of the cell membrane may become detached. The exposed pieces of lipid bilayer folds back on itself, encapsulating a small packet of whatever solution it forms in. This happens because of the hydrophobic and hydrophilic interactions between the pieces of lipid bilayer and the surrounding aqueous solution. It forces the ends of the pieces, where the hydrophobic core is exposed, to come together and create a sealed internal pouch. This process can be replicated in the lab.

Using a sonic wave generator, scientists can use sonic waves to break apart lipid bilayer membranes into any size liposome they want. The sonic waves carry energy, which pulls apart the molecules of the bilayer and separates it into pieces. These pieces are then subject to the same forces that naturally occurring liposomes are created by, and fold into the same shape.

What is a Liposome Used For?

Liposomes have been used as models, to study cell membranes and organelles. By embedding various proteins into the lipid bilayer, scientists can test the function of those proteins by testing the internal solution compared to the external solution. Studies like this helped establish modern cell theory. In fact, liposomes were named after lysosomes because of their similarity to the organelle. By studying non-living, easy-to-watch actions in liposomes, scientists were able to predict and identify the methods cells used to move and transport various chemicals. The actions of the endoplasmic reticulum and Golgi apparatus, in packaging and processing cell products, is directly related to how liposomes interact. Cells simply add various proteins to the surface of their organelles, which direct and control the interactions of various organelles. These processes are now being studied, so that the targeted effect it gives organelles can be extended to artificially created liposomes.

On this front, drugs are being developed which have a liposome delivery method. For instance, certain cancer drugs are packaged in liposomes to be delivered specifically to cancer cells. The theory behind this method is simple. The liposomes are embedded with special proteins, which attach to receptor proteins on the target cell. Once this happens, a process is initiated and the liposome bonds with the target cell, depositing its contents into the cell. Research into liposome delivery systems is expanding into different areas including vitamins, minerals, and even gene therapy. By using targeted liposomes, even DNA can be delivered to specific tissues. If the DNA is functional, it can be read and the protein it encodes for can be produces. The cell can then begin to produce the protein and reverse the deficiency. This process may soon be used to alleviate various genetic diseases.

Other industries are developing liposomes for different uses. Because a liposome is essentially a small cell, it is biodegradable over time but can still carry an aqueous solution in a protected manner. Scientist are working on using this feature to develop liposomes which can carry out complicated tasks. Some of these application include delivering nutrients to crops using liposomes as small machines. If the right “machinery”, or DNA and related proteins, are placed in a liposome it essentially becomes a small living cell which can be programmed to preform various actions. While commercial versions of this are not in effect, much research is being done on this front.

Quiz

1. What is the difference between a micelle and a liposome?
A. A liposome is made of a single layer
B. A micelle has an internal compartment which can store water
C. A liposome is composed of a bilayer, rather than a single layer

Answer to Question #1

C is correct. A micelle is formed of a single layer and has no internal compartment. A micelle is formed from chemicals like soap, which are both hydrophobic and hydrophilic. These tend to form small micelles, which can be felt as the slipperiness of soap on your fingers.

2. True or False. A liposome contains specialized enzymes.
A. True
B. False

Answer to Question #2

B is correct. Technically speaking, a liposome contains anything it was formed around. It could contain those enzymes, but does not have to. Remember that lysosomes are specialized organelles which do contain a variety or specialized digestive enzymes. While these organelles resemble liposomes, they are much more complex because they must interact with a variety of other cellular components.

3. How could liposomes be used to clean up environmental hazards?
A. Impossible!
B. Package the liposomes with enzymes to process the hazard
C. Spray liposomes onto the ocean

Answer to Question #3

B is correct. Several research projects are being established around the idea of using specialized liposomes to clean up environmental toxins. For instance, if the DNA encoding for an enzyme which could breakdown oil were introduced into a liposome along with the machinery to produce the enzyme, the small package could survive a long time, continuously breaking down oil. An added benefit would be that the entire package would be biodegradable itself.

References

• Lodish, H., Berk, A., Kaiser, C. A., Krieger, M., Scott, M. P., Bretscher, A., . . . Matsudaira, P. (2008). Molecular Cell Biology (6th ed.). New York: W.H. Freeman and Company.


• Nelson, D. L., & Cox, M. M. (2008). Principles of Biochemistry. New York: W.H. Freeman and Company.

Liposome

Ectotherm

Ectotherm Definition

An ectotherm is an organism which derives the heat it requires from the environment. This is in contrast to an endotherm, which creates the heat it needs from internal chemical reactions. A common misconception is that an ectotherm is “cold-blooded”. An ectotherm can regulate its temperature behaviorally, by moving into warmer areas or positioning themselves to reduce heat loss. Therefore, while many ectotherms allow their body temperatures to drop during periods of inactivity, they usually maintain body temperatures in ranges similar to mammals while they are active. An ectotherm can be a thermoregulator or a thermoconformer, depending on if it actively changes its body temperature. There are also a number of pro and cons to being an ectotherm. These topics will be addressed below.

Thermoregulation in an Ectotherm

The common misconception around ectotherms being cold-blooded comes a misunderstanding of how these animals work. All animals need some sort of heat energy for the chemical reactions in their bodies to take place. Endotherms derive this heat from the breakdown of energy rich tissues like fats and through quick muscular contractions, known as shivering. These processes release heat, which is then distributed through the body via the circulatory system. Likewise, an ectotherm also uses the circulatory system to distribute the heat throughout its body, but the heat comes from a different source.

Instead of relying almost solely on the energy in their food for heat, ectotherms use radiant heat provided by the environment. This heat can be gained in many ways. Solar radiation is the most common way, as many ectotherms use the sun’s rays to warm up. Another way is through conduction. Rocks and the ground soak up solar energy, and over time they radiate that energy out in the form of infrared radiation. An ectotherm can also position itself near or on things that are radiating heat to absorb that heat. Thermoregulating ectotherms take advantage of this, and build their body heat up to substantial levels before periods of activity. Then, usually at nighttime, an ectotherm will let its body temperature drop, as it doesn’t need the extra heat. Evaporation of water and conduction of heat away from the organism cause heat loss. A thermoregulating ectotherm will also behavior adaptations to deal with these losses, such as hiding in a burrow or minimizing evaporation through body posture and breathing.

There are also thermoconforming ectotherms. A thermoconformer is an animal which does little to nothing to change its body temperature. A thermoconforming ectotherm is also known as a poikilotherm. Consider most fish for example. Water has the ability to sap heat out of an organism very quickly. As fish breathe, water passes directly over their gills and cools their blood. As a consequence, most fish are the same temperature as water around them. They do not shiver or bask in sunlight when they are cold, their maximum activity level simply decreases. Some ectothermic animals even live in freezing environments, and use specialized ions and antifreeze molecules to keep their cells from freezing. Others, like many invertebrates, simply freeze and wait to be thawed out. On the other end of the spectrum, there are also large fish like tunas and sharks which keep their body temperatures higher through specialized circulation patterns and high levels of activity. Some have even argued that these fish could be endothermic to a certain degree.

Thus, how an ectotherm can thermoregulate varies widely. There exists an entire spectrum within the category of ectotherm which includes all these methods of regulating temperature. That being said, very few ectotherms actually have “cold” blood. Compared to humans and other endotherms, they simply allow their body temperatures to fluctuate much more. While it may seem like endotherms are somehow “more evolved” or more complex, this is simply not the case. As all organisms alive today have been evolving for the same amount of time, the fact that there are both endotherms and ectotherms means that both systems have their benefits and faults. In fact, by number of species and overall biomass, the ectotherms far outweigh the endotherms. This is because being an ectotherm has a number of pros and only a few cons.

Pros and Cons of Being an Ectotherm

Pros

Ectotherms have a distinct advantage over endotherms when it comes to energy usage. Mammals typically use about 98% of their energy to maintain their body temperature. This means that they can maintain high activity levels nearly all the time, but it also means that they can only use about 2% of the energy in their food for growth and reproduction. An ectotherm does not have this problem. Most ectotherms use over 50% of the energy in their food for growth and reproduction. This means that ectotherms can survive on much less food than similarly sized endotherms. An ectotherm can simply let its body cool off at night, reducing the amount of food needed for survival. The graph below shows the ability of an ectotherm to survive over a wider variety of internal temperatures.

The ability to allow body temperature to fluctuate gives a number of other distinct advantages. A reduced body temperature means cellular processes go slower, decreasing the total metabolism. This is important for fish and other creatures which live in freezing waters over winter. All in all, it has been found that an ectotherm uses approximately one-tenth of the energy that an endotherm uses. These energy savings translate directly into faster growth and more reproduction. Where a bird may lay several eggs, a similarly sized reptile will lay hundreds. However, ectotherms also face distinct limitations.

Cons

Mammals and other endotherms developed for a reason: there was a niche to be filled that ectothermic animals could not compete in. Because ectotherms tend to lower their activity levels periodically, they are vulnerable to predation. Whether you are basking in the sun or falling asleep because your body temperature is dropping, many ectotherm behaviors are risky. Endotherms do not have this drop in energy level every day, and therefore are more ready to react to danger. Note of the graph above that this also means ectotherms have a lower overall activity level. While this is a major flaw, it has not stopped millions of ectotherms.

The second major problem that excludes ectotherms from certain environments is temperature. Many mammals and birds are able to live where ectotherms cannot. These animals use adaptations like hair and feathers to insulate themselves from temperature extremes. Other ectotherms, like those in the desert, have a hard time maintaining their water balance because it is directly tied to their heating and cooling mechanism. As seen in the examples below, many ectotherms have strange behavioral adaptations which allow them to compensate for these problems.

Examples of an Ectotherm

Galapagos Iguanas

The Galapagos iguana (Amblyrhynchus cristatus), also called the Marine iguana, is a perfect example of a thermoregulating ectotherm. In the morning, the iguana emerges from its burrow, and takes a position on a black lava rock. The iguana’s temperature is really low, as the iguana let it fall overnight. As the sun strikes the iguana and the rocks around it, the iguana absorbs the solar and infrared radiation striking its body. It will even turn the largest surface area of its body towards the sun, much like a solar panel, to absorb the maximum amount of heat. Eventually, the iguana is hot, and ready to be active, as seen in the image below. Marine iguanas are special in that they forage underwater for algae.

The iguana runs off the cliffs, and plunges into the cold ocean water. The water quickly starts drawing the heat out of the iguana’s body. It must hurry to feed before it is too cold to move its muscles. While the iguanas can hold their breath for over 30 minutes, they must return to the shore shortly after this to start regaining heat. The iguana returns to the surface after feeding, and swims to shore. It must now climb back up the cliffs and start reabsorbing heat. In this way, the iguana is actively regulating its temperature to provide itself with enough heat to efficiently feed. At night, the iguana will return to its burrow and assume a much lower body temperature, close to that of the air.

Tree Frogs

Tree frogs are an ectotherm which have a different set of problems. The rainforest is a very warm place, even at night. Most tree frogs do not necessarily have to lower their activity levels at night. Their temperature cycle is usually based on a different phenomenon: that of evaporation. During the day, trees absorb water from the ground and transfer it to the air above the canopy. By the afternoon, the air is saturated, and it begins to rain. This constant water cycle also affects the tree frogs. As the air dries out in the hottest part of the day, the water from the frog begins to evaporate away. This not only dries the frog out, but reduces the frog’s body temperature as well.

But tree frogs aren’t without their tricks. Some frogs will jump into bodies of water during this part of the day, as standing water is usually fairly warm and they won’t lose water to evaporation. Other frogs have adapted strange poses, which protect their most sensitive areas from losing water. Then, when the afternoon rains begin to come down, the frogs can begin hunting and feeding on insect. This times perfectly with the coming of nighttime, when many insects emerge.

Freezing Fish

The final example is of a non-regulating ectotherm. Several species of fish exist in waters so cold that normal fish would freeze. For water to become ice, it needs a couple of factors to exist. First, it must be cold enough. Second, there must be some sort of molecule which acts as a “seed” for ice crystals to establish on. Lastly, the water must not contain molecules which prevent ice formation. Fish which exist in these conditions are poikilotherms, or ectotherms which do not regulate. While these animals do not need much heat to maintain their activity levels, they do prevent themselves from freezing.

These animals both actively filter impurities from their blood and create special proteins which prevent ice from forming. This allows the animals to exist in temperatures far below freezing, with freezing themselves. Salt water doesn’t freeze until much lower temperatures because of the dissolved salts, but the water inside animal cells is much less salty, and should freeze before saltwater. A normal fish would freeze from the gills almost instantly in these waters. These fish prevent this from happening and are able to thrive in a niche others cannot reach.

Quiz

1. Which of the following is an ectotherm?
A. Zebra
B. Ostrich
C. Snake

Answer to Question #1

C is correct. Both the zebra and ostrich regulate their body temperature using non-behavioral means such as burning fat and ATP. The snake must rely on energy from the environment. If it is cold, the snake will not be able to hunt or move about, where the zebra and ostrich can operate in much more varied temperature extremes.

2. What is one advantage of being an ectotherm?
A. You are warm all the time
B. You use considerably less energy to regulate your temperature
C. You can gather food at any temperature

Answer to Question #2

B is correct. Without the need to maintain a body temperature, an ectotherm can use considerably less energy. This means that more energy can be devoted to growth and reproduction per unit of food that the animal obtains.

3. You found a new animal. You monitor it throughout the day and see that its temperature fluctuates a lot. You also see that it actively moves itself to different positions when its temperature reaches certain extremes. This animal is a:
A. Poikilotherm
B. Endotherm
C. Ectotherm

Answer to Question #3

C is correct. This animal would be a thermoregulating ectotherm. It likes to warm up during the day, and actively controls its temperature through behavioral modifications.

References

• Brusca, R. C., & Brusca, G. J. (2003). Invertebrates. Sunderland, MA: Sinauer Associates, Inc.


• Helfman, G. S., Collette, B. B., Facey, D. E., & Bowen, B. W. (2009). The Diversity of Fishes: Biology, Evolution, and Ecology. Oxford: Wiley-Blackwell.


• Pough, F. H., Andrews, R. M., Cadle, J. E., Crump, M. L., Savitzky, A. H., & Wells, K. D. (2004). Herpetology. Upper Saddle River, NJ: Pearson Prentice Hall.

Ectotherm

Apoplexy

Apoplexy Definition and Explanation

Apoplexy is a term used to describe internal bleeding and the accompanying symptoms. Historically, the term originated in the medical profession to describe the phenomenon of patients becoming suddenly weak and becoming unconscious. It was not well understood why an apoplexy would occur until the mid to late 1800s. Patients could have been bleeding from an internal organ or from vessels in their brain, and the diagnosis was still apoplexy. The symptoms include everything from dizziness, confusion, weakness, and loss of consciousness. Eventually it was understood that an apoplexy arises from internal bleeding, and can happen in a wide variety of organs and tissues.

Once this was understood the term was eventually phased out, and replaced by more specific terms which describe exactly where the bleeding is occurring. An ovarian apoplexy, for example, is weakness and unconsciousness caused by bleeding in the ovaries. A cerebral apoplexy can now be more accurately described based on advanced imaging of the brain. An brain aneurysm, or a balloon-like enlargement of blood vessels in the brain, may cause apoplexy if it leaks blood, ruptures completely, or even puts pressure on other vessels and parts of the brain. Thus, doctors now prefer to not refer to simply an apoplexy, but describe the actual organ and vessel losing blood and causing the patient to lose consciousness.

It should also be noted that apoplexy has also been used to describe frustration, in a metaphorical manner. Historically, it was assumed that tension on the arteries caused apoplexy. Thus, people associated it with being overly frustrated and stressed out. We now understand that diet and exercise are more responsible for clogged arteries. It is unlikely that a healthy person can simply become frustrated enough to start bleeding internally.

Quiz

1. Why is the term apoplexy slightly ambiguous?
A. It does not describe where the bleeding is occurring
B. It has been used it the past to metaphorically describe frustration
C. Both of the above

Answer to Question #1

C is correct. Apoplexy was originally used because no one understood the cause of the sudden unconsciousness. We now know that it is caused by internal bleeding, and use different and more specific terms to identify which tissues or organs are bleeding. Further, if a non-medical professional says they experienced apoplexy, they could simply be speaking hyperbolically.

References

• Black, J. R. (1875). Apoplexy. Popular Science Monthly(6), 705-709.


• Dictionary.com. (2018, 2 15). Apoplexy. Retrieved from DIctionary.com: http://www.dictionary.com/browse/apoplexy

Apoplexy

Carrion

Carrion Definition and Explanation

Carrion is dead animal matter, which may also be actively decaying. Any animal which dies leaves a carcass, or the remains of their body. This material is eaten by scavengers, and is further reduced to small pieces of organic material known as detritus. Carrion serves as a major source of food for many carnivores and omnivores.

Both vertebrates and invertebrates utilize carrion as a source of food, particularly protein. All carnivores and omnivores eat carrion, but to different extents. Using comparative anatomy, scientists can study the teeth and digestive tract of an organism to understand if it eats a lot of carrion. Felines and animals like ferrets are obligate carnivores, and prefer live prey. Their teeth and digestive tract reflect this. Their canines are long, sharp, and much larger than their other teeth. This is for incapacitating live prey with a bite to the neck or throat. They also have very sharp teeth used for slicing and swallowing whole chunks of meat. Meat is easy to digest, and as such these organisms have shortened digestive tracts.

On the other hand, omnivores like dogs and bears that feed on a lot of carrion have distinct changes to their dentition. These animals have molars in the back of their jaw, which help to grind and separate tough tissues like bone and cartilage. They also have sharp teeth and large canines, but not to the extent that the felines do. If you look at the colon of a carrion eater, you will see it is usually relatively longer than that of an obligate carnivore, as these animals must be able to process every scrap of food they can find. A similar case can be found in birds. Birds which eat carrion have sharp beaks and talons to tear bite-size chucks from a carcass. Many fish and aquatic animals specialize on carrion, such as the lamprey, hagfish, and piranha.

Besides the carnivorous vertebrates, there are a number of invertebrates that specialize on carrion. Crabs, for example, provide an essential service of breaking down carrion and spreading the nutrients around. Many worms, insects and other small invertebrates also help with the breakdown of a large carcass. The reproductive lifecycle of many of these insects includes a larval stage (such as a maggot) which feeds on carrion. At a certain point, when the pieces of carrion are so small that only the smallest organisms like ants, worms, and bacteria can feed on them, they are known as detritus. Detritus is further broken down by these tiny organisms (detritivores) into organic nutrients, which can then be absorbed by plants and used to build new tissue. Thus the cycle of life continues.

References

• Brusca, R. C., & Brusca, G. J. (2003). Invertebrates. Sunderland, MA: Sinauer Associates, Inc.


• Feldhamer, G. A., Drickamer, L. C., Vessey, S. H., Merritt, J. F., & Krajewski, C. (2007). Mammology: Adaptation, Diversity, Ecology (3rd ed.). Baltimore: The Johns Hopkins University Press.

Carrion

Prone Position

Prone Position Definition

The prone position is an anatomical term used to describe an organism with its ventral side against the ground. For a human and similar animals, this means laying on their stomach. It also means that the limbs are not extended, and that the organism is not standing or sitting. This can be seen in the following image. In the image, you can also see the supine position, which is similar to prone, except that the organism is on its back or dorsal side.

Uses of Prone Position

The prone position has many uses across different industries. In the medical field, the position is used to preform many different procedures. Amongst these are surgeries to the back, therapeutic massage, and various biopsies spots for different tissues. This position gives access to many tissues, including the spine, kidneys, lungs, muscles, and many others. Still other professionals will have their patients lie prone for therapies like acupuncture, various allergy tests, and a wide variety of other reasons.

However, it is not only the medical field which employs the prone position. It is also used widely in various exercise programs, as a starting point and resting position. Yoga, for instance, uses it before going to various poses which stretch and strengthen the back. Other types of stretching and muscle building also require the use of the position. The military, police force, and shooting sports enthusiasts use the prone position to create stability and increase their accuracy. The increased number of contact points with the body and the ground increase the stability of a shooter.

Lastly, behavioral scientists can observe animals in the prone position and draw different conclusions about their behavior and health. Not all animals use the prone position in the same way. A cat in the prone position could either mean it is stalking prey, or relaxing. The position of the legs determine which of these is true. A stalking cat in the prone position will still have its legs tucked under it, ready to pounce. Some animals never use the prone position, and indications of their health can be quickly made if seen in this position. A bat, for instance, would never find itself in the prone position unless it has fallen to the ground. This would indicate that the bat underwent trauma, is sick, or is debilitated in some other way.

References

• De luliis, G., & Pulera, D. (2007). The Dissection of Vertebrates. Amsterdam: Academic Press.


• Nakos, G., Batistatou, A., Galiatsou, E., Konstanti, E., Koulouras, V., Kanavarous, P., . . . Bai, M. (2006). Lung and ‘end organ’ injury due to mechanical ventilation in animals: comparison between the prone and supine positions. Critical Care, 10(1), R38.

Prone Position

Supine Position

Supine Position Definition

The supine position is a term used in anatomy and medicine to describe an organism on its back. This position can be used to describe any organism with clear dorsal and ventral sides. In the supine position, the dorsal side, or back, goes towards the ground. The ventral side then points toward the sky. The supine position is opposed to the prone position, where an animal or person is lying on their stomach. This can be seen in the image below.

Uses of Supine Position

The supine position is used in a number of fields to orient a specimen, subject, or person into the correct orientation. For instance, many surgeries are conducted in the supine position to allow access to the majority of the internal organs. Other surgeries, like certain back surgeries, must be conducted with the patient in the prone position to allow access to the dorsal side of the spine. Other doctors may study how a patient sleeps using the supine position. A polysomnograph is a test done on a sleeping person which records how they sleep in various positions, supine included. The supine position is also used in veterinary medicine to position animals on their backs for various procedures.

Other, non-medical professionals also use the position. In comparative anatomy scientists may place two different specimens in the supine position to compare their ventral anatomical features. In rehabilitation, sports training, weight-lifting, and yoga, the supine position is an important starting position. From this position you can begin a wide variety of exercises and stretches. It should be noted that while the supine position is in general any position with the subject on its back, many professions and fields may have specific adjustments or nuances that accompany their field.

References

• De luliis, G., & Pulera, D. (2007). The Dissection of Vertebrates. Amsterdam: Academic Press.


• Nakos, G., Batistatou, A., Galiatsou, E., Konstanti, E., Koulouras, V., Kanavarous, P., . . . Bai, M. (2006). Lung and ‘end organ’ injury due to mechanical ventilation in animals: comparison between the prone and supine positions. Critical Care, 10(1), R38.

Supine Position

Nuclear Fallout

Nuclear Fallout Definition

Nuclear fallout is a destructive, long-term consequence following large-scale releases of radioactivity into the environment. Radioactivity is the transfer of energy through waves or particles, and is common in the world. Light, for instance, can have a radioactive source and is not harmful by itself. However, human created scenarios in which the nuclei of atoms are ripped apart release large amounts of radioactive particles and energy. These events, like nuclear bombs and nuclear reactor meltdowns, pour radioactive substances into the air and water.

Radiation causes a number of chemical reactions, changing elements and creating dangerously reactive charged particles, or ions. Further, X-rays and gamma rays can be released by the splitting particles. These waves carry tremendous energy and can easily disrupt living systems and mutate DNA. As particle and waves are release into the air, they can travel long distances before finally settling back to the Earth. The nuclear fallout, with its devastating effects, happens in the area where the particle reach. Some nuclear fallouts reach a global scale, while others are limited to a localized area.

Nuclear Fallout Radius

The size of the area affected by nuclear fallout is entirely dependent on the type and quantity of radiation exposure. While many nuclear isotopes are handled and produced every day for commercial and medical applications, these industries rarely operate on the scale or with reactive enough isotopes to cause a nuclear fallout. Two human activities have been responsible for large-scale nuclear fallout events throughout history. Nuclear weapons were the first human invention to cause fallout.

A nuclear blast will create nuclear fallout in an area proportionate to the size and quality of the bomb, and adjusted for where the bomb is detonated. Two main types of nuclear weapons exist: fission bombs and fusion bombs. Fission bombs release energy by smashing two pieces of uranium together, causing individual atoms to fuse together. This releases a lot of energy. The first atomic bomb dropped in wartime, a bomb named “Little Boy” dropped by the United States on Japan, was a fission bomb. The bomb produced a blast equivalent to 15 thousand tons of TNT. Below is an image of the initial blast radius, and the fires it produced. The bomb exploded in the air, before reaching the ground. This is known as an “air blast”, and sends radiation into the atmosphere and into the surroundings as nuclear fallout. This small, preliminary bomb had a blast radius of about a mile. Measurements of the fallout were not accurately obtained, but it is assumed that the radioactivity travels tens or hundreds of miles in the surrounding air.

The largest nuclear bomb to be set off was the “Tsar Bomba” or “King of Bombs”, detonated by the Soviet Union in 1961. The bomb was a fusion bomb, which relies on the energy created in a fission reaction to spark a much more powerful fusion reaction between atoms of hydrogen. Bombs in this class are therefore called hydrogen bombs, H-bombs, or thermonuclear weapons. The Tsar Bomba was the largest ever built in this class. The mushroom cloud created by the explosion could be seen for hundreds of miles. The resulting nuclear fallout from the explosion was condemned by the United States and led to escalations in the Cold War. It is believed that nuclear fallout from this, and hundreds of other nuclear weapons tests, can carry nuclear fallout around the globe, as the explosion reaches straight into the upper atmosphere. It can take weeks or months for the radioactive materials to make their way to ground, and they can travel thousands of miles. This nuclear fallout causes an increase in chemically reactive ions, radioactive isotopes, and causes mutation and even death in living organisms.

The true threat of a nuclear war is not in the localized effects of the bomb, or even the leveling of entire cities, but of the possibility of a global nuclear fallout. If multiple weapons of this size and quality were detonated around the same time, radioactive isotopes would descend on all parts of the globe. Global food and water supplies would quickly become tainted and most people would starve to death or die from radiation poisoning within a few years.

The second invention of humanity to cause nuclear fallout was based on the theory of nuclear weapons, but meant to aid humanity. Nuclear power uses the energy from splitting atoms and converts it to electrical energy. Today, nearly 20% of the United States energy is produced using nuclear. Many countries have turned to this method as a high-yield energy source. However, there have also been many disasters caused by the nuclear energy industry. One of the most significant, the leak at the plant in Chernobyl, Russia, caused a nuclear fallout which has lasted decades and caused significant health effects for citizens of surrounding countries. Cancers have been found which can be specifically linked to the radioactive isotopes released by the plant. More recently, the reactor core at the Fukushima Daiichi Nuclear Power Plant in Japan was severely damaged by an earthquake and tsunami.

The initial radiation leakage in these events was not known. In the case of Fukushima, it was assumed that the radioactivity was sealed off, until explorations by radioactively-shielded robots revealed groundwater seeping into the facility. While very few deaths have been directly reported from the incident, it is still unknown how far reaching the nuclear fallout is, and who will be affected. Initial reports warned of the radioactivity leaking into the sea, which could carry it worldwide. As advanced instrumentation is required to detect and classify nuclear radiation, the best bet for avoiding nuclear fallout is to get as far away from the source as possible, as quickly as possible.

How Long Does Nuclear Fallout Last?

As with the size of the area affected by nuclear fallout, the length of time an area will remain affected is determined by the amount of radioactivity release. Radioactive isotopes have a specific rate at which they decay. This is known as the half-life of a radioactive material, as half of the material will decay in that amount of time. Some radioactive chemicals are present in nature, from the forming of the stars and planets. We can use these isotopes, like Carbon-14, to date ancient objects by measuring the amount of Carbon-14 they have compared to their surroundings. Other radioactive isotopes are produced by the human inventions discussed above, and can produce toxic and long-lasting isotopes. Plutonium-239, for instance, has a half-life of 24,600 years. This means that leftover plutonium from nukes and nuclear energy production will give off radiation for hundreds of thousands of years to come.

That being said, the radiation levels in a fallout area after a nuclear blast tend to subside quickly. Weather events like rain can help to wash away the radiation and ions created by the blast. Some blasts have been found with lower levels of radiation after only a few weeks, while other events leave radiation for many years. The Fukushima disaster, for instance, will take 30 to 40 years to clean up entirely. However, the surrounding areas will be free of radiation long before that. Further, while nuclear fallout can last weeks to months, the health effects from it will be seen for many decades after. Many health effects of radioactivity are seen as cancers which develop after the energy from radiation has mutated DNA. The more immediate effects of radiation poisoning and contaminated food and water supplies can be replaced and replenished more quickly.

How to Survive Nuclear Fallout

The best way to survive a nuclear fallout is to leave. The area affected by a nuclear fallout will likely not be safe anywhere. Dust and particles carried in the air will be radioactive, and contaminate anything they touch. Local water supplies will become radioactive and should be avoided, as drinking from them or using them to bathe will result in radiation poisoning. Considering that all historical nuclear fallout events have been mostly localized, traveling only a few hundred miles is usually sufficient to protect yourself from radiation.

However, in the event of a global nuclear fallout, the option to flee is no longer viable. In this case, you must obtain enough food, water, and energy to survive several months or even years before the radiation subsides. During the Cold War, a large business sprang up installing nuclear fallout shelters. The basics of a shelter are simple: put as much dense material between you and the radiation as possible. Several simple designs consist of digging a hole in the ground, and covering it with a thick material. Supplying oneself with enough food and water in this case is difficult, which is why worried homeowners often turned to underground bunkers, complete with years of food and water. The walls were often lined with lead, tungsten, or other dense metals to block radiation.

While this scenario was hyped during the Cold War and many retreats were created, the feasibility of surviving a nuclear fallout is unknown. Critics contend that radiation would still get in through the air ducts or water supply, and that no one can be truly safe. This has led some to say that the best way to survive nuclear fallout is to avoid it altogether, and put bans on nuclear weapons and energy.

References

• Beck, J. E. (2013). Introduction to Environmental Health. Dubuque: Kendall Hunt Publishing Company.


• Hampel, V. E. (1986). United States Patent No. 4,625,468.


• Williams, D. (2002). Cancer after nuclear fallout: lessons from the Chernobyl accident. Nature Reviews Cancer, 543-549.

Nuclear Fallout

Horticulture

Horticulture Definition

Horticulture is the field of study which concentrates on gardening, and the plants and biological systems which make up a garden. Horticulture is a broad science which has many sub-disciplines. Horticulture studies both the science behind the garden and the aesthetics which make it appealing to look at. For instance, floriculture focuses on the production of flowers, while viticulture studies purely grapes. Horticulturalist can find themselves in a variety of positions, from maintaining community gardens to curating plants in a museum. Horticulture also overlaps with several other sciences, discussed below.

Horticulture vs Agriculture vs Botany

Horticulture is derived from Greek, and literally means “garden cultivation”. Agriculture has similar Greek roots, but means “field cultivation”. As can be seen by their roots, the words differ in mostly scale. However, history has shaped them to be even further apart. While horticulture is concerned with many species and how they can occupy a tight space, agriculture focuses on producing large amounts of a single species. Agriculture is also concerned with the production of animals for food and other products, which horticulture is not.

Botany in another science concerned with plants. However, botanists tend to focus on the plants themselves, the unique anatomy which makes them up, and the chemical processes which drive their lives. Horticulture is more concerned with how these plants live and reproduce, and what means can be used to nourish, harvest, and sustain the plants in a garden. It is also concerned with making the plants appear attractive and appealing to a viewer. While the difference may seem arbitrary, these specialties tend to serve very different segments of the economy. Agriculturalists and botanists focus on large-scale production of crops, while the horticulturalist focuses many varieties and how they can be combined both logically and aesthetically. Horticulture provides humanity with new varieties and methods of gardening, which can then be implemented on larger-scales.

Careers in Horticulture

Horticulture is broken into various subfields, which specialize in certain types of plants. A degree in one of these fields can be obtained from the associate’s level through doctorate levels. The lower degrees are required for handling and maintaining plants and gardens, while a doctoral candidate might do research on the plants or try to develop a new variety. Below are several of the many different paths in horticulture.

Arboriculture is the study of trees and how they grow. These professionals may work for tree grooming services, which artistically cut trees in a manner which allows the tree to continue growing. Arboriculturists are also responsible for monitoring and maintaining fruit trees. Grafting, a popular technique used to mix species of plants, can be used by these scientists to produce trees which can produce several kinds of fruit. Other horticulture scientists specialize in flowers, vegetables or fruits. Often, these plants have delicate environments which need to be maintained for maximum plant health and harvest. Horticulturists understand which plants can be planted where in a garden, for maximum beauty and yield.

Another section of horticulture is turf management. Golf courses, hotels, and many luxury establishments have large areas of grass which need extensive management to maintain their beauty. Professionals in this field specialize in grasses and the unique care regiment they need to stay green and lush year-round in some places. Along the same lines, a landscape horticulturalist understands not only the plants which make a great landscape, but also the aesthetics and art which really create beautiful properties. These professionals may own their own business as general contractors and get hired by members of the community to spruce up their property.

Still other areas of horticulture focus in on the cultivation of specific plants. Viticulture is the study of grapes, for the making of wine. Every variety of grapes makes a different kind of wine, and wine-makers always have an experienced viticulturist to guide their efforts. Even simple grapes are actually a complex organism which requires the perfect conditions to produce the sugars needed for making wines. The study of horticulture informs this practice and it has been perfected to an art form. However, the battle between nature and man is never resolved.

In the coming years, horticulturalists will face a slew of new enemies. Changing weather patterns will affect the growth and success of plants. It may also usher in new pests and diseases that must be dealt with. A garden, while created by man, is controlled by nature. Horticulture gives man the tools to combat nature, and guide the garden to be productive and fruitful.

References

• American Society for Horticultural Science. (2018, 2 7). What is Horticulture? Retrieved from ashs.org: http://www.ashs.org/?page=horticulture


• McMahon, M. J., Kofranek, A. M., & Rubatzky, V. E. (2011). Plant Science: Growth, Development, and Utilization of Cultivated Plants (5th ed.). Boston: Prentince Hall.


• University of Minnesota. (2018, 2 7). Why Horticulture? Retrieved from Department of Horticultural Science: https://horticulture.umn.edu/students/why-horticulture

Horticulture

Biomechanics

Biomechanics Definition

Biomechanics is an interdisciplinary field that applies the principles of physics to biological systems to understand how organism move and interact with their surroundings. Biomechanics is concerned with everything from microscopic systems like muscle contraction in cells, all the way to large-scale, whole-body motions like a jumping cat. Biomechanics applies the laws of physics with regards to levers, pulleys and other known functions to define and understand the complicated forces involved in biological systems. A career in biomechanics means studying biological systems and learning from them or creating devices based on a combination of biological and physical principles.

History of Biomechanics

Biomechanics has a long and intricate history, reaching back to the days of Aristotle and the first philosophers. These men sought to understand the driving forces behind life, and as such, they studied how animals moved and what caused those actions. Building on their successes, the thinkers of the Renaissance added to these notions. Leonard DaVinci is still known for his works of anatomy and physiology, which incorporated some of the first math-driven biomechanics on record. Modern biomechanical engineers have followed in their footsteps.

The ideas behind biomechanics gained footing in the 1500s, with the writings of Descartes, and others that saw the world in a mechanic way. Thus was born the science of automatons, or the idea that all creatures were simply biological machines that reacted to stimuli in the same way a machine would. This idea has captivated scientists for hundreds of years, as it would give the ultimate ability to control and manipulate these machines. However, as science progressed, the complexities of the living machines became infinitely intricate. The field branched into many subdivisions.

Modern biomechanics has innumerable advantages over the early pioneers of the science. Modern technology can provide insights and measurements that science has never before been able to obtain. For instance, a greater understanding of nerve impulses came after the invention of the EEG, a test in which a computer monitors the electrical signals passed between cells. Further advances into microbiology and chemistry have revealed the internal microscopic structure of muscles. This allows biomechanical engineers to have a full and clear view of the body and how it works. These advancements have not been left to waste. New advancements in biomechanics and biotechnology are allowing for novel treatments like artificial limb and organ replacement. Not only can science produce new joints for old bodies, but the science has advanced far enough that we can now grow organs using specialized stem cells sprayed onto 3D printed models. The possibilities of biomechanics are expanding rapidly.

Careers in Biomechanics

Pathways to a career in biomechanics can vary, but almost always include engineering and biology courses. General Bachelor’s degrees are offered which provide introduction to biomechanics, but most professionals have a Master’s degree or higher. Further coursework is often needed beyond a Bachelor’s degree to understand the complex math and biology underlying the field. It is not rare for a biomechanical engineer to receive a degree in engineering and a medical doctorate. However, once the field is understood the possibilities are limitless.

Medicinal biomechanics deals with the human body, and is involved in everything from replacing limbs and organs to understanding the complex forces athletes deal with while playing sports. Orthotics and Prosthesis are the fields that deal with replacing lost or missing limbs. These scientist integrate invention with biology as they seek to reverse debilitating conditions. Others, like those who study sports biomechanics, focus on physics involved during complex sports. These professionals provide estimates for the damage being done, and ways to avoid that damage, like wearing a helmet. Still others focus on the strain of repetitive tasks. The field of ergonomics studies the body’s natural position and how stresses are created. Still others, like rehabilitation specialists, practice biomechanics to give bedridden patients zero-strain exercise.

Other scientists use biomechanics for different reasons. Understanding the physics of an animal can often lead to understandings about its role in the environment. Ecologists and other field-scientists use biomechanics to understand the different stresses on an organism. They could measure the strain a tree faces in the wind or measure the amount of friction a dolphin experiences while it is swimming. These observations can lead to understanding about the animal or ecosystem or even lead to novel devices to help humans. Modern biomechanical engineers often employ computers in their modeling. This is known as computational biomechanics and will lead to greater understanding of all biological systems. Experts in this area also have training in computer information systems to exploit the power of modern computers in their studies.

References

• De luliis, G., & Pulera, D. (2007). The Dissection of Vertebrates. Amsterdam: Academic Press.


• Nelson, D. L., & Cox, M. M. (2008). Principles of Biochemistry. New York: W.H. Freeman and Company.


• Rollin, B. E. (2006). Animal Rights and Human Morality (3rd ed.). New York: Prometheus Books.

Biomechanics

Toxicology

Toxicology Definition

Toxicology is the study of how an organism reacts to various concentrations of chemicals. Toxicologist use model organisms to test various chemicals and estimate the concentration of chemical which can cause effects. Chemicals which will be used to produce goods used by people will undergo rigorous testing to ensure their safety. Toxicology also focuses on the structure of poisons, toxins, and venoms. Advanced methods, such as Nuclear Magnetic Resonance Spectroscopy, are used in toxicology to classify new toxins and understand their chemical structure. As we understand more about the world around us and seek to use new chemicals to our advantage, toxicologists are continually presented with a broader field of study.

History of Toxicology

Toxicology is an ancient science. Since the dawn of man, humans have sought to understand and manipulate the substances found in their environment. Ancient Roman and Middle-Eastern and Asian texts have descriptions of toxins along with their treatments. While ancient forms of the field relied on various belief in magic, the influence of stars, and other fantastical origins to explain and cure the effects of toxins, modern toxicology is a much more scientific pursuit.

Many fields have influenced and informed toxicology, and our understanding of chemicals and their interactions in general. A general understanding of chemistry and biology allowed the father of toxicology, Mathieu Orfila, to publish the first work on toxicology in 1813. Orfila went on to establish forensic toxicology by using his techniques to find evidence of arsenic in the body of a murder victim. Since the 1800’s toxicology has greatly expanded and advanced. Today, toxicology contains many branches of study and specialization.

Careers in Toxicology

While some schools have Bachelor’s and Master’s level toxicology programs, the majority of toxicologist go on to receive a PhD and specialize in a certain area of toxicology. Many area of toxicology exist, but in general toxicologists focus on a few themes and specialize from there. Medicinal toxicology is the branch most concerned with humans and what we are exposed to. Many toxicologists in this field work for government organizations or testing labs, and approve the products released to consumers. Others in this field understand toxins and poisoning and assist criminal investigators as forensic toxicologists. Everyone with a human focus on toxicology must understand human biology, and most are medical doctors that specialize in toxins.

Another area of toxicology focuses on the toxins themselves, and the species that produce the toxins. Because the chemicals in venom and animal toxins are so biologically active, they are extremely interesting for academics and pharmacists alike. For instance, a mycotoxicologist studies the toxins produced by fungi and their relatives. Many professionals studying toxicology study how the toxins form, act on their target, and eventually break down. This information is crucial to those on the defending edge of toxicology, like the doctors treating deadly snake-bites or accidental poisonings. Others search for ways to use the effects of the toxin in therapeutic ways. Venom, toxins in plants, and other biologically active substances could possibly be used to target specific unwanted cells or simply shut down nerves temporarily. A key convention in toxicology is that the dose makes the poison. In other words, the way we use chemicals determines their effect on us. Pharmaceutical companies are very interested in using toxins in beneficial ways, and hire toxicologist to research and analyze new chemicals.

The final focus in toxicology is of a broader scope. Ecotoxicologist, a combination of ecology and toxicology, study toxins in a larger context, and how they affect ecosystems and populations. Organizations like the Environmental Protection Agency employ toxicologists to study and monitor the health of the environment and discover potential disruptive toxins. It is this branch of toxicology that is responsible for the discovery of PCBs affecting the ozone and of the pesticide DDT reducing populations of eagles. Using the same tools as their peers, these scientists try to isolate and detect large-scale sources of potentially environmentally hazardous materials. Since the chemical revolution of the 1960’s, this branch of toxicology has expanded rapidly. Books like Silent Spring, by Rachel Carson, helped shed light on environmental destruction being caused by unregulated chemical usage. Since then, many organizations have been created to monitor and try to control the spread of dangerous substances.

Ethics and Technology in Toxicology

Toxicology has always required the use of model organisms in testing. To understand the effects of a new chemical, toxicologists first introduce the chemical to these model organisms. The effects of the chemical in different concentrations and doses are observed. This helps inform scientists of how the chemical reacts with living cells in general, and how it can specifically irritate or mutate cells. The most common of these tests involves exposing a test population to varied concentrations until half of the organisms are dead. Throughout history, different organism have been used as models, with different ethical implications.

Traditionally, some reprehensible methods have been employed in testing toxicology. From experiments on human prisoners to forced toxin inhalation tests in primates, toxicology is one of many branches of science with a dark history of morally questionable experiments. While these more questionable practices have been phased out and abolished, the need for experimentation still exists. The chemical revolution of the 1960’s created millions of new commercial and agricultural chemicals. Poor practices in toxicology led to epidemics like the use of the insecticide DDT, which ended up affecting the thickness of bird eggs and greatly reduced populations of birds of prey. Modern organizations, like the FDA, test chemicals and products for various industries before they are allowed to be sold or used commercially.

While there is still a need for experimentation, the methods of experimenting have changed drastically. New methods include testing chemicals on non-sentient organisms such as bacteria, yeast, and other single-celled organisms. The effects found in observing these smaller organisms can be extrapolated to other organisms. For products that must be tested on higher organisms, limits have been set on the number of subjects needed and animals are not allowed to suffer. These methods have created a more ethics-friendly toxicology. However, even more advanced methods of computational toxicology are emerging and will soon replace animal models completely. Computer simulations and understanding of chemistry and biology has advanced to a point that toxicology simulations can now be carried out by the computer. Advances in this field may lead to the elimination of model organisms all together, and the ethics of testing would be much more agreeable for scientists.

References

• American Chemical Society. (2018, February 5). Toxicology. Retrieved from ACS.org: https://www.acs.org/content/acs/en/careers/college-to-career/chemistry-careers/toxicology.html


• Nelson, D. L., & Cox, M. M. (2008). Principles of Biochemistry. New York: W.H. Freeman and Company.


• Rollin, B. E. (2006). Animal Rights and Human Morality (3rd ed.). New York: Prometheus Books.


• Sarkar, S. (2005). Biodiversity and Environmental Philosophy: an introduction. New York: Cambridge University Press.

Toxicology

Copepod

Copepod Definition

The term copepod is used to describe small crustacean species that are found in the majority of aquatic environments. Copepods can be found in both the upper waters and bottom of oceans and freshwater bodies, as well as swamps, bogs, ponds, and other wet habitats. Copepods constitute an important zooplankton species.

Copepod Lifecycle

The copepod lifecycle is similar to that of other crustaceans. The lifecycle begins with an egg that hatches into a larval form that contains a head and tail without a defined abdominal region, known as the nauplius (shown below). After several rounds of molting, the larva achieves adulthood. Adult reproduction is dictated by seasonal cues and the relative abundance of nutrients. Moreover, the presence of environmental toxins and water quality have also been found to alter copepod reproduction and development.

Copepod Characteristics

The following are several common copepod characteristics:

• Copepod size varies from 2 mm to 1 cm in length.


• The body of copepods is teardrop-shaped, contains a thin, almost transparent exoskeleton, and two pair of antennae (shown below).


• Copepods lack a circulatory system and gills. Instead, oxygen is absorbed directly via the skin.


• Waste products are excreted via specialized maxillary glands.


• The copepod body consists of several segments: 5-7 thoracic segments, upon which the head and limbs attach and an abdomen, which is devoid of limbs but can form a tail-like structure. The shape and size of the body is highly variable depending on the specific species.


• Most copepods contain one centrally-located compound eye; however, some species lack an eye.


• Specialized thoracic appendages called maxillipeds are used for feeding.

What Do Copepods Eat?

Copepods residing near the surface of large water bodies typically consume phytoplankton or other copepod species. Species residing on the ocean floor or other similar habitats have specialized mouth parts that are capable of scraping organic waste products and associated bacteria for consumption. Other copepods are parasitic species and will derive nutrients from a host (shown below). Some copepods feed on insect larvae and are being tested for their ability to control mosquito populations in regions affected by mosquito-transmitted diseases (e.g., dengue).

Quiz

1. A nauplius is:
A. A singular red eye found on copepods.
B. A specialized eating appendage.
C. The larval form of a copepod.
D. A type of parasitic copepod.

Answer to Question #1

C is correct. A nauplius refers to the larval form of copepods.

2. Which of the following statements is NOT true about copepods?
A. Many copepods consume phytoplankton.
B. Copepods are generally small but are highly variable in size.
C. Copepods lack both a defined circulatory and respiratory system.
D. Copepods live in a wide range of habitats from swamps to arid deserts.

Answer to Question #2

D is correct. Copepods inhabit aquatic environments and would not survive in an arid desert climate.

References

• Andreadis et al. (2018). Amblyospora khaliulini (Microsporidia: Amblyosporidae): Investigations on its life cycle and ecology in Aedes communis (Diptera: Culicidae) and Acanthocyclops vernalis (Copepoda: Cyclopidae) with redescription of the species. J Invertebr Pathol.151:113-125.


• Atkinson, A. (1998). Life cycle strategies of epipelagic copepods in the Southern Ocean. Journal of Marine Systems.15; 289-311.


• Groner et al. (2016). Lessons from sea louse and salmon epidemiology. Philos Trans R Soc Lond B Biol Sci. 5;371.


• Harrison, JF. (2015). Handling and Use of Oxygen by Pancrustaceans: Conserved Patterns and the Evolution of Respiratory Structures. Intergr Comp Biol. 55(5):802-15.


• Yen, J. (2000). Life in transition: balancing inertial and viscous forces by planktonic copepods. Biol Bull. 198(2):213-24.

Copepod

Marine Snow

Marine Snow Definition

Marine snow refers to organic particulate matter that constantly falls from the upper waters into the deeper waters of the ocean. Marine snow serves to provide food and energy from the productive upper waters exposed to sunlight to the marine organisms that reside in the deeper regions of the water column. The content and abundance of marine snow varies seasonally and with variations in ocean currents. This is largely due to the seasonal changes in light and resources available to the organisms in the upper water column.

Marine Snow Characteristics

Marine snow is comprised of primarily organic particulate matter derived from the bodies of phytoplankton, feces, and decaying plant materials. These particulates typically join to form larger aggregates that are coated in mucus created by bacterial, zooplankton, and phytoplankton species. As these aggregates sink toward the ocean floor, they often accumulate additional particles, and can grow up to several centimeters in size. Since the abundance of marine snow changes with the seasons and nutrient abundance in the upper waters, the abundance of marine snow often increases during algae blooms (pictured below) as a result of increased phytoplankton growth. It is also hypothesized that marine snow is involved in nutrient recycling within marine environments. In this way, the particulates both provide food for the organisms that reside in the deep waters, but also help to decompose the organic matter residing at the ocean floor (e.g., fecal matter) via the bacterial species that comprise the particulates of marine snow.

Quiz

1. Which of the following is NOT a feature of marine snow?
A. Marine snow is comprised primarily of inorganic matter.
B. Marine snow is more abundant during the winter months.
C. Marine snow is toxic to organisms that reside in the deeper waters of the ocean.
D. None of the above are features of marine snow.

Answer to Question #1

D is correct. None of these responses are features of marine snow. Marine snow is comprised primarily of organic matter derived from organisms that reside at the surface waters, such as phytoplankton. Since these organisms depend on sunlight and nutrient availability, there is typically a greater abundance of marine snow during the summer months. Marine snow is a food source to many organisms that reside within the deeper waters, and thus is an effective means of moving energy through the water column. Thus, marine snow is not toxic to the animals inhabiting the deeper regions of the ocean.

References

• “Marine snow falls heaviest at the Equator.” (2017). Nature. Oct 1e1;550(7675):158. doi: 10.1038/550158b.


• Sun et al. (2017). Light-induced aggregation of microbial exopolymeric substances. Chemoshere. Aug;181:675-681.


• Tansel, B. (2018). Morphology, composition and aggregation mechanisms of soft bioflocs in marine snow and activated sludge: A comparative review. J Environ Mange. 205:231-243.

Marine Snow