Friday, September 28, 2018

Elf


In the woods you happen across a clearing full of strangely beautiful people. At first you think they may be human, but upon closer examination you discover that their features are too fair and perfect to have come from mortal man. You walk into the clearing to get a better look and introduce yourself, but happen to step inside a ring of mushrooms and flattened grass. Their expressions quickly turn from curiosity to wrathful anger.

Suddenly you begin to feel ill. You reach out to apologize and explain your actions, but they are already disappearing into the depths of the forest. It is too late. As punishment for your offense, you have been elf-shot.


What is an Elf?


An elf is a mythical creature that appears to be human in nature, but has magical powers and does not age (or at least ages very slowly). It appears that elves have their origins in Germanic lore, but they are also commonly found in other European folklore.


Elf


The elves are seen as a ‘luminous’ group of people who are known to have fair complexions far more perfect than even the most beautiful human features. They are sometimes known as ‘the white people.’ It is thought that this is either a reference to their pure morality or, perhaps as a reference to their beauty and pale features.


Elves were seen as both a point of fear and curiosity in early societies. They were often known to be sociable and even friendly to humans, but they were still greatly feared because of their temper. If they perceived a human to have harmed or offended them in any way, they were quick to retaliate with a punishment. Common punishments included illness, night terrors, and cruel tricks and attacks directed towards the victim. It is noted, however, that the elves did sometimes help cure sicknesses in some instances.


Elves and Birth


The elves are a curious legend indeed. Although they are thought to never age (or to live for hundreds of years depending on which storyline you follow), the elves were thought to need human assistance to bring their children into the world. This help was often thought to be needed from mid-wives who could safely deliver the children and from wet-nurses. While midwives have a pattern of being married to preachers, the wet-nurses were normally women who had recently given birth. This caused great fear in many early European households.


While both of these groups of women had something to fear from traveling to the Elven world, the wet-nurses were especially terrified of their fate. They were normally taken from their newborns and families to the Elven world to take care of the newborn Elf babies. While this doesn’t seem to be nefarious, it would have been frightening for any woman who was put in this situation. It was rumored that eating any food offered in the Elven world or taking any hospitality from them would keep a person from ever returning to the human world. It is unclear if these rules held to the wet-nurses – who obviously had to spend a prolonged period of time in their world, but the fear of being barred from returning to their families would have been enough to give them great fright.


It was also common for midwives to be called upon to help bring elven babies into the world. It is unknown why a midwife was needed, but it was common knowledge at the time that a human midwife was needed to deliver a elf child. Usually, a midwife who was married to a preacher was called upon to perform the necessary duties. It was important that the midwife who was called did not eat or drink while in the Elf world for the above reasons. Some stories say that the midwives (who usually had time to prepare unlike the kidnapped wet-nurses) would sometimes pack food and water to take with them so that they could keep themselves from becoming hungry. There are several tales of midwives being summoned that were widely accepted in their day.


Peter Rahm’s Wife is Summoned


A clergyman by the name of Peter Rahm was known to have told a tale of his wife being summoned to help a mythical being give birth. She went with the creature and performed her duties. After the child was born, the grateful couple offered the midwife food and drink. She kindly refused. They offered her other forms of hospitality which she refused as well. She was sent on her way and returned home. The next day she found a pile of silver pieces – a gift from the new parents for delivering their child.


A Danish Story of An Elf and his Earthwife


A Danish tale tells of an Earthman (an elf) who sought the help of a midwife on Christmas Eve. He took the midwife underground and had her attend to his Earthwife during labor. When the child was delivered, the elven husband took the child away – seeking to steal the good fortune of a newly wed couple for the child. While he was gone, the elf wife gave the midwife a warning. She warned the woman against eating any food or taking any drink while she was under the surface of the earth. She told the midwife that she too had been a Christian woman before she was invited into the realm of the elves but had made the mistake of eating their food while she visited. Because she had accepted their hospitality, she was unable to return to her own world. When the husband returned, the midwife refused the offers of hospitality. Because of this, she was allowed to return to her home.


Elves and Their Relationships with Humans


While there seemed to be a great many ways that elves could threaten the safety of a human being, there were some elves who lived in peace with humans and even formed relationships with them.


Human and Elf

Human and Elf


While there are some accounts of elves who tried to seduce humans into having sexual relations with them, it appears that there were some humans and elves who had children consensually. These children were known to be especially beautiful and often went on to do great things.


More often than not, half-elf half-human children appeared to be human in their features (though they were often very beautiful) and were capable of great magic feats. They sometimes went on to become magicians, sorcerers, and healers.


There are several ballads and stories concerning elves who mate with humans. They usually involve some sort of riddle that the person must solve in order to become their lover. Some stories also require the character to rescue a human-turned-elf in order to win their lover’s hand in marriage.


The Elfin Knight


The Elfin Knight is a story that can be told in two manners. The first is that the knight threatens to steal a woman away to be his lover unless she can complete an impossible task. The second is that a woman must complete an impossible task in order to win the Knight’s hand in marriage. Over time, the second has become more popular.


The tale starts with the Knight blowing into a magic horn that causes desire to emerge in the heart of the maiden. She makes a wish that she could marry the Knight. Suddenly the Elfin Knight appears and tells her that he will marry her if she can perform several tasks – all impossible.


In return, the maiden responds with several impossible tasks of her own that the Knight must complete and wins the hand of Knight in marriage.


The Tale of Tam Lin


The tale of Tam Lin begins with a warning that Tam Lin is an elf who takes a possession or the virginity of any maiden that travels through the forest of Carterhaugh. One day, a young woman travels through the forest of Carterhaugh and plucks a double rose from the ground. Tam Lin appears and asks her why she has entered his forest and taken his possessions. She replies that Caterhaugh belongs to her – it was a gift from her father. The young maiden goes on her way, only to discover later that she had become pregnant.


Tam Lin

Tam Lin’s Well, Carterhaugh


She returns to the forest and plucks another set of roses from the ground. Tam Lin appears again to challenge her actions. She asks him if he had ever been a human, or if he has always been an elf. He tells the maiden that he had once been a mortal but was captured by the Queen of Fairies and turned into an elf. He also reveals that he is afraid that he will be sacrificed in a tithe to Hell this year if she does not save him.


Together they devise a plan to rescue Tam Lin from the Fairy Queen. They enact the plan and the maiden wins the love of Tam Lin. The Queen of Fairies acknowledges her defeat and releases Tam Lin.


Lady Isabel and the Elf Knight


Unfortunately, not all relationships between elves and humans end well. The tale of Lady Isabel and the Elf Knight starts the same as ‘The Elfin Knight’ with the Knight blowing into a horn that causes desire to arise in the heart of Lady Isabel. She wishes that she could marry the Knight and he appears and tells her that she will be his wife if she will come with him to the greenwood.


Upon arriving at the greenwood, Lady Isabel is shocked when the Knight reveals that he has killed the daughters of seven kings to steal their treasures and possessions and intends to make her the eighth. Fortunately, Lady Isabel is a quick thinker and tells the Knight to put his head on her knee to rest together before she is to die. She then lulls him to sleep with a charm, binds him with his own belt, and kills him.


What Do Elves Look Like?


The majority of elves that are described in folklore are female, though there were certainly male elves as well. The description of an elf’s appearance varies depending on the time period and the location that the story takes place in. It appears that the majority of female elves are known to be fair creatures. They often have blonde hair and blue or grey eyes (these are also the features that they value in humans) and are known to have characteristics that are similar to humans but much more perfect in nature. There are, of course, some variations in their appearance. These characteristics however, are the most commonly used in fairy tales.


Male elves were often described as looking like old men, though this is not the case for all the elves that appeared in literature. There are also extremely handsome elves that appear and seduce women like the elves from Tam Lin and The Elfin Knight.


Most literature will describe elves as being human in shape and size. They are known to have especially fair features and are sometimes described as being even taller than the average human. Writers in Shakespeare’s time however, took a different approach in describing elves. They were transformed into tiny beings who often had wings and were surprisingly similar to fairies. This version of elf was known to enjoy playing tricks on humans.


Modern literature tends to take a blended perspective on elves. While you can still find the occasional reference to elves being small beings, there are also plenty of storylines that present elves as being roughly human-sized.


Where Do Elves Live?


The majority of storylines will claim that elves either inhabit homes that are deep inside the woods, carved into hollowed trees, or underneath the earth (often in a hill). This was fairly standard for the majority of supernatural creatures in early Europe.


Most people have lost their faith in the existence of the elves, but there still remains a large population who maintain their beliefs – or are at least open to the possibility – of the existence of elves in Iceland. The people of Iceland have taken special precautions to ensure that the homes of their beloved huldufolk are protected in modern day.


The Huldufolk Stop Construction Near Alftanes


In the Alfantes peninsula, road work has been proposed in an area that was thought to be frequented by the elves of Iceland. There were many protests against the construction on the grounds that it would ruin the habitat of the elves as well as the natural landscape. The protest caused the entire project to be halted until the Supreme Court of Iceland rules on the case.


This is not an isolated occurrence. Other roads that were proposed to be built in areas where elves were thought to live were stopped by strange equipment malfunctions or tools suddenly being stolen from the worksite. Some think that these incidents were caused by elves themselves.


Interestingly enough, a law was passed in 2012 forbidding construction in any area that was believed to be inhabited by elves or was culturally or historically significant otherwise to Iceland.


Dangers Posed by Elves


Elves and Sickness


Elves were often thought to be the cause of many sicknesses that could not be diagnosed or properly treated by a doctor. It was thought that elves were capable of living parallel to the human world (though invisible to the human eye) and would make a person sick if they felt offended by the individual. This was said to be accomplished in several ways. Sometimes a person became sick if an elf casted a spell over them. Other times, however, an elf could shoot a man with an invisible arrow that carried sickness. Therefore, it was not uncommon for people to be diagnosed as being ‘elf-shot’ when they were ill.


Elves were also thought to bring about other misfortunes that were connected with health – specifically sleeping. The German word Alpdruck means ‘nightmare’, but the literal translation means ‘elf oppression.’ From this, it can be assumed that elves were thought to be the cause of nightmares and night terrors – likely as a punishment for an offense that had been made towards them or as a cruel joke.


Curiously, it seems that elves were often blamed when an individual became afflicted with epilepsy. This is possibly because of the complicated nature of the illness and the lack of medical resources available to treat such an ailment.


Elves and Alchemy


Elves were known to be magical beings, so it is no surprise that they were often credited with several types of magic. There are many different types of magic credited to elves, but one of the most popular by today’s standards was alchemy.


Elf markwoman

Elf markwoman


Alchemy was a scientific and philosophical practice that was aimed at purifying different elements. One of the most popular types of alchemy recognized by humans was the practice of taking an earth element (usually some type of metal) and attempting to transform it into a precious metal like silver or gold.


The elfin tie to alchemy is likely why there are so many stories that reference an elf giving a human something that appeared to be worthless (like charcoal) that had magically transformed into gold by the time they had returned home.


Elves and Seduction


Another common threat that elves were thought to hold over humans was seduction. For some reason, elves had many desires to lure humans into sexual relations with them and were often warned against in tales.


Some elves were recorded to be very forceful with this desire. At some point, the notion arose that male elves would force themselves on women while they were sleeping. This issue was reported in the Scottish witch trials, and the elves in the tales were interpreted as being an alias for the Devil himself.


Elves and Changelings


Curiously enough, it was thought that elves sometimes valued human babies over their own kind. There was much speculation for why this may be, but there were two main theories. The first was that the elves were fond of the human babies that they stole because of their fair hair and blue or grey eyes. The second was that the children were stolen to use in a tithe to Hell so that the elves would not have to sacrifice one of their own. Regardless of what their motivation was, human parents came to dread the thought of losing their child to the elves.


It was thought that when an elf came to steal away a child, it left one of it’s own in place of the stolen infant. This elf child was known as a ‘changeling.’ These infants appeared to be human, but were often afflicted with unexplained illnesses. To discover a changeling in place of a human baby was a serious situation. Often, due to the many issues that came with changelings and their noticeable need to eat more than a human baby, changelings were killed before they had a chance to reach early childhood. It was thought that to let the changeling live was to put the resources of the entire family in jeopardy, making infanticide the best option for the unlucky couple.


Origin of the Elf Myth


Arisen from Cain’s Murder of Able


Some sources seem to think that the elves may have arisen from Cain’s murder of Able. This is the case in Beowulf, which clearly states that elves came to be a race because of this unfortunate event.


Semi-Banished Angels


Other sources seem to think that elves may have been the angels who chose to stay neutral in the fight for Heaven with God facing off against Lucifer. They were banished from Heaven because they did not help God, but because they did not betray him they were not sentenced to Hell. Instead, they were banished to Earth, where they would be come to known as elves.


Lost Children Of Eve


An old Icelandic tale suggests that elves could be the lost children of Eve. The tale states that one day when God was walking through the Garden of Eden, Eve was embarrassed that her children were dirty. She told them to go and hide from God so that she would not have to be embarrassed by God seeing them in their condition.


When God walked up to Eve and asked her where her children were, she lied and said she didn’t know. Angry that she would dare to lie to him, God said, “That which man hides from God, God will hide from man.” From that day forward, Eve never saw her children again.


The tale goes on to suggest that the children became the huldufolk (the hidden people [elves]) of Iceland.


Reborn into Elves


The Germanic tales which are thought to inspire the first stories of the elves suggest that these beings could be created by the rebirth of the dead. The old Norse texts seem to imply that worship of the elves and worship of dead ancestors are one and the same. This suggests that a person can be reborn into a supernatural creature like the elf when they pass on to the afterlife.


Evidence of this belief can be found in tales like ‘The Saga of Olaf the Holy’ in which the king’s ancestor has a burial mound that is marked as ‘Olaf, the Elf of Geirstad.’ This reflects the belief that the king’s ancestor became an elf in the afterlife.


The Explanation of Strange Occurrences


Last but not least, it is certainly possible that elves were simply created as a way to explain the unexplainable at the time. This is evidenced by some of the most common events that were blamed on elves – like elf-locks (when a strand of hair was found to be knotted).


This would have also helped people to reconcile with unfortunate events like the birth of a deformed baby. It certainly would have been easier to dispose of a child that put the new family at risk if it was thought to be an elf changeling instead of their own offspring.



Elf

Tuesday, September 18, 2018

Transferrin

Transferrin Definition


Transferrin is a crucial glycoprotein that shuttles iron in the blood. It would be an understatement to say that iron is vital for most life-sustaining processes. Transferrin has become an important biomarker for good health in the clinical setting, as it can reveal if a patient has functional iron depletion. This bio-marker, of course, will give a physician insight into a patient’s pathology, as well as which treatment plan will be most suitable moving forward.


Transferrin Structure


Transferrin

Transferrin


The image above is a 3-D depiction of human transferrin protein.


Structurally speaking, Transferrin is a polypeptide chain consisting of two carbohydrate chains and almost seven hundred amino acids. Transferrin has two homologous globular lobes, the N- and C- terminals comprised of alpha helices and beta sheets, with an iron binding site in between. The site itself is a six iron coordinate site occupied by a carbonate anion and four residues.


Each lobe is further divided into two clefts, or domains. Importantly, this structure lends transferrin the ability to undergo large conformational changes upon needing iron to be taken up or released. This is made possible by the rotating domains that rotate around a screw axis. Through x-ray crystallography, scientists have uncovered the mechanism for iron-release. This lies in how two of the basic residues from two of the domains will create a special hydrogen bond under neutral pH; however, this bond will break and thus release iron in the acidic pH of the endosome at its delivery site. Each transferrin molecule is able to carry two iron molecules in the bloodstream, and we will discuss in more detail the importance of sheltering iron until it is needed.


Transferrin Function


Iron is found everywhere on earth, and so it is no surprise that it also vital to sustaining life. Humans use iron for many cellular processes but perhaps the most important is iron’s ability to bind oxygen. As we know, oxygen is fundamental to cellular respiration and it is therefore necessary to transport oxygen from our lungs to each individual aerobic cell – without letting radical oxygen roam freely and ravage our cell’s membranes! Safe shuttling through our circulatory system is the answer. While humans contain about 3.7 grams of iron in our bodies, much of which comes from our diets, 2.5 grams will be “locked” inside hemoglobin with iron. Hemoglobin can then assume its role in transporting oxygen through the blood. However, just as importantly, we have evolved a way of recycling and storing this iron for future use. This is where transferrin comes in.


Plasma transferrin is a crucial player in iron metabolism. Transferrin essentially limits the levels of free iron in the blood. Free iron is dangerous in that it carries the risk of triggering free radical reactions, which sets off lipid oxidation and the destruction of thousands of molecules. Free radicals are defined as having at least one unpaired electron and they will thus be driven to steal electrons from every cell tissue including the heart, pancreas, brain, etc. Iron-triggered free radical damage can thus contribute to heart and liver disease, neurological issues, and more. Thankfully, transferrin binds essentially all circulating plasma iron. This chelation makes iron soluble and non-toxic as it is being delivered to tissues, accordingly serving the functions of rendering iron soluble, preventing iron-triggered free radical damage, and transporting iron. Transferrin, in fact, is the most valuable source of iron for red blood cells, with the highest turnover. The transferrin that circulates the blood is made and secreted by the liver. As previously mentioned, Transferrin can bind two iron ions. This is accomplished thanks its built-in iron (Fe3+) binding sites which have an extremely high affinity for iron. Lending to this affinity is an anion cofactor (preferably carbonate anion), that in its absence will make iron and transferrin binding negligible. The remaining four coordination sites are those from the transferrin molecule including an aspartic carboxylate oxygen, two tyrosine phenolate oxygens, and a histidine nitrogen. At any given time, about one third of the transferrin’s binding sites are filled. Upon radioactively labeling transferrin, it was found that about eighty percent of its iron was delivered to the bone marrow and then integrated into newly formed red blood cells. Other sites of delivery included the liver and spleen, which are major storage sites. It is said that of the 3 grams of iron found in adult human males, only about 0.1 percent of it ends up circulating in the plasma.


Clinical Significance of Transferrin


Tests measuring the levels of transferrin saturation are ordered when a healthcare provider suspects a patient has anemia. Symptoms may include pale coloration, fatigue, irritability, and shortness of breath. Anemia is defined as having low numbers of red blood cells, however one type is categorized by iron-deficiency. When iron levels run low in our bodies’ stores, our livers will upregulate transferrin synthesis in the healthy individual. Iron is necessary for hemoglobin synthesis, and thus having low levels of accessible iron will impede this process. Of course, there are multiple causes for anemia, which brings us to the Transferrin Saturation or Total Iron-Binding Capacity (TIBC) blood test. This test will determine if the underlying problem lies at the level of transferrin. This test checks how many of the possible transferrin binding sites end up “saturated,” or filled. In healthy individuals, transferrin levels range between 170 to 370 mg/dl and the percent saturated should lie between twenty and fifty percent. However, in severe iron-deficient cases this percentage may fall to under ten percent. Transferrin-iron saturation percentage will be low in patients with iron deficiency, and treatment options may include iron supplements or even blood transfusions.


Quiz


1. Which of the following best describes a main role of transferrin?
A. Systemic transportation of oxygen
B. Initiating radical pathways
C. Reducing levels of free iron
D. Preventing all anemia types

Answer to Question #1
C is correct. Like its name indicates, Transferrin transports and transfers iron. In doing so, this chelation will reduce levels of free iron which has the essential function of preventing secondary radical oxidative stress. While iron does help red blood cells carry oxygen, hemoglobin is the molecule that transports oxygen.

2. Which of the following was discussed as being necessary for transferrin-iron binding?
A. Oxygen
B. Carbonate
C. Calcium
D. Copper

Answer to Question #2
B is correct. While transferrin and iron can bind without assistance, the presence of a carbonate anion will lend transferrin its impactful fullest high affinity binding and is thus necessary.

References



  • Mizutani, Kimihiko et al. “X-ray structures of transferrins and related proteins, Biochimica et Biophysica Acta (BBA) – General Subjects, Volume 1820, Issue 3, 2012, Pages 203-211, ISSN 0304-4165. https://doi.org/10.1016/j.bbagen.2011.08.003.

  • Goodsell, David (2002). “Ferritin and Transferrin: molecule of the month.” PDB-101. Accessed 1 May 2018 from <http://pdb101.rcsb.org/motm/35>

  • Harvard BWH (2001). “Iron Transport and Cellular Uptake.” Accessed 1 May 2018 from <http://sickle.bwh.harvard.edu/iron_transport.html>

  • Iron Disorders Institute (2009). “How Iron Triggers Free Radical Activity.” Last accessed 2 May 2018 from <http://www.irondisorders.org/iron-tiggers-free-radical-activity>

  • University of Rochester Medical Center (2018). “Transferrin.” URMC Health Encyclopedia. Last accessed 2 May 2018 from <https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=transferrin>



Transferrin

Lipolysis

Lipolysis Definition


Lipolysis is the process by which fats are broken down in our bodies through enzymes and water, or hydrolysis. Lipolysis occurs in our adipose tissue stores, which are the fatty tissues that cushion and line our bodies and organs. In fact, fats can be thought of simply as stored energy. Fats are ready and available for when our glucose stores run low between meals, and it makes sense for lipolysis to occur as it will facilitate the movement of these stored fats through our bloodstream. Breaking down this “potential energy” into free moving fatty acids can then allow them to be repurposed or expended as fuel!


Lipolysis actually has links to various processes within our bodies. Free fatty acids are vital cell-to-cell communicators, are a staple ingredient of gluconeogenesis and cellular respiration, and can upregulate the transcription of proteins like the uncoupling proton channels that line our mitochondrial membrane – which will inhibit ATP synthesis without disrupting the respiratory chain. In sum, lipolysis is a key life-sustaining biological process; although, as of late, it’s taken on new meaning at cosmetic clinics around the world for its promise to zap unwanted fat! While for their namesake, both processes technically “lyse” or break fats, the way in which they accomplish this is obviously different – the latter utilizing cool lasers or heat to reduce fat cells.


Lipolysis Mechanism


Triglycerides are undoubtedly the main energy molecule in eukaryotic cells. Triglyceride is a glycerol derivative that is stored as lipid droplets within our fatty tissues, and herein lipolysis takes place. Let’s begin by describing lipolysis in big picture scope. These lipid droplets are first targeted by lipolytic enzymes that are highly regulated and will access these droplets in the event of phosphorylation.


These lipases will ensue to sequentially hydrolyze our triglycerides into their glycerol and fatty acid components until we are left with sole glycerols, and this takes place with three enzyme reactions. The breakdown of fats is termed beta-oxidation, or “fatty acid” oxidation because the triglycerides are being oxidized into their most basic functional parts. We are thus left with free fatty acids and glycerol that can enter other metabolic pathways or find new purpose. Let’s dive into specifics.


Lipolysis Mechanism

Figure 1


The image depicts the Lipolysis mechanism, breakdown of triglycerides into fatty acids and glycerol.


The first and rate-limiting step of lipolysis involves the enzyme, adipose triglyceride lipase (or ATGL), which is sensitive to hormones. The ATGL will hydrolyze our triacylglycerol into a diacylglycerol, losing a free fatty acid that will be free to mobilize in our bloodstream. The resultant diacylglycerol will then be acted upon by hormone-sensitive lipase (HSL), which will remove another fatty acid to give a monoacylglycerol molecule. Finally, monoacylglycerol lipase (MGL) will break the monacylglycerol further down to a single glycerol molecule.


The figure below illustrates the main “destinies,” if you will, of the resulting fatty acids and glycerol. Fatty acids can undergo beta-oxidation and repurpose to create Acetyl-CoA. Of course, Acetyl-CoA is best known as a vital starting molecule that initiates the Krebs’s cycle in cellular respiration. This repurposing is vital when glucose stores are low in times of starvation, or even between meals, as cellular respiration can continue to run and sustain life. Similarly, the free glycerol can enter glycolysis. Normally glucose is converted to G6P at the first step of glycolysis. In the event that glucose levels are low, glycerol will be converted to dihydroxyacetone phosphate and will enter glycolysis at the second control point to keep glycolysis running. Thus, fats make the best energy store as they will ensure that cellular respiration continues to run and ATP is produced.


Lypolosis

Figure 2


The figure illustrates Lipolysis and the pathways the fatty acids and glycerol components take.


Lipolysis Regulation


Like every vital biological process, lipolysis is regulated to meet our needs. At any given time, it would be extremely harmful to have tons of free fatty acids flowing through our bloodstream. Anyone with high cholesterol or arterial plaques will attest to that. Thus, lipolysis – and its inverse process, lipogenesis – need to be counter-regulated and highly sensitive to the levels of specific hormones and proteins. For example, stimulatory hormones like, epinephrine, norepinephrine, cortisol, glucagon, and growth hormone induce lipolysis. Key hormones glucagon and epinephrine will use the same pathways to induce lipolysis with minor differences.


Both glucagon and epinephrine will serve as ligands that will bind to G-protein coupled receptors on the surface of fat cells. The G proteins will then activate adenylate cyclase and upregulate their conversion of ATP to cAMP. We might recognize cAMP as the famously ubiquitous secondary messenger of so many other biological pathways. Likewise, here the cAMP will activate protein kinase A (PKA), which will expend an ATP molecule in phosphorylating and upregulating the hydrolysis activity of our HSL enzyme – otherwise known as our second enzyme in the lipolysis pathway. As a result, we are left with free fatty acids and glycerol that can then enter metabolic pathways to counter the low sugars in our blood, for instance. Understandably, HSL was thought to be the rate-determining enzyme of lipolysis for some time before TAG lipase (or ATG, our first enzyme) was uncovered to be the key initiative lipolytic step. Let’s quickly take a look at why it makes sense for glucagon and epinephrine to trigger lipolysis.


Glucagon-induced Lipolysis


Glucagon is a peptide hormone that is synthesized by pancreatic cells in the event that glucose and thus insulin levels drop. Glucagon will then trigger our liver to break down its glycogen stores and release much needed glucose into our blood. Conversely, when our glucose and insulin levels are high, insulin in healthy individuals will allow glucose to exit the bloodstream and be taken up by insulin-dependent tissues. Of course, in diabetics, the tissues will no longer respond well to insulin and this sugar will not reach the tissues and instead cause havoc in the bloodstream.


Shifting back our focus to lipolysis, glucagon stores are small and will be expended quickly. Fat stores, on the other hand, are vast and ready to use. Here, glucagon serves its key role. Glucagon will bind to Glucagon G-protein coupled receptors on fat cell membranes, and trigger the HSL-activating pathway described earlier. The glycerol that is released can then travel to the liver or kidney where it will be eventually converted to GA3P and enter glycolysis and our gluconeogenesis pathway to synthesis badly needed glucose (refer to figure 2).


Epinephrine-induced Lipolysis


Metabolism

Figure 3


The diagram specifically illustrates epinephrine-induced Lipolysis through a G-protein mediated pathway.


Epinephrine will also bind G-protein receptors on fat cell membranes, however they will specifically bind beta-adrenergic receptors. This binding will likewise lead to the cAMP/PKA-led phosphorylation of hormone sensitive lipase, that will ultimately drive the release of free fatty acids and glycerol. Epinephrine is known for its connection to our instinctual “fight or flight” response. This hyperarousal occurs when we perceive an attack or threat to our survival. Thus, it makes sense that epinephrine would trigger lipolysis and its resulting up-drive of metabolic processes. If we are ever starving, our body will certainly react to this threat and use our fatty energy stores to respond and sustain life at all costs.


Lipolysis in Popular Culture


As briefly mentioned above, a fun fact is that lipolysis has become a popular term in the cosmetic world. Not to be confused with the adipose lipolysis pathways detailed in this article, laser lipolysis and even injection lipolysis are clinically proven methods of reducing the number of fat cells without liposuction surgery. Noninvasive fat reduction has become a new cosmetic staple, and promises to target fat cells through the use of heat, cooling (via lasers or radiofrequencies), or less commonly deoxycholic acid injections without disrupting surrounding tissues.


Quiz


1. Which of the following enzymes is the rate determining enzyme in lipolysis?
A. HSL
B. ATGL
C. MGL
D. None of the above

Answer to Question #1
B is correct. As mentioned above, researchers uncovered that the first lipolysis step, mediated by ATGL, is coincidentally the rate determining step of lipolysis. It was previously thought to be HSL as it undergoes phosphorylation.

2. Which of the following will induce lipolysis?
A. High insulin/Low epinephrine
B. High insulin/High epinephrine
C. Low insulin/High epinephrine
D. Low insulin/Low epinephrine

Answer to Question #2
C is correct. Low insulin and high epinephrine will trigger lipolysis. This makes sense if our body is constantly responding to feedback. When glucose and insulin levels are low, we will need fats to sustain gluconeogenesis and cellular respiration. High epinephrine will occur in the face of a life threat that will require the orchestration of fat energy expenditure.

References



  • Binienda, Z et al. “Role of Free Fatty Acids in Physiological Conditions and Mitochondrial Dysfunction.” SCIRP: Food and Nutrition Sciences, Vol. 4 No. 9A, 2013. Retrieved <http://www.scirp.org/journal/PaperInformation.aspx?PaperID=36092>

  • American Society of Plastic Surgeons (2018). “Nonsurgical Fat Reduction: Minimally Invasive Procedures.” Plasticsurgery.org. Accessed 2018, May 29 from <https://www.plasticsurgery.org/cosmetic-procedures/nonsurgical-fat-reduction/laser-lipolysis>

  • Ward, Colin (2015). “Lipolysis and Lipogenesis.” Diapedia: 51040851148 rev. no. 17. Accessed 29 May 2018 from <https://www.diapedia.org/metabolism-insulin-and-other-hormones/51040851148/lipolysis-and-lipogenesis>

  • Engelking, Larry R. (2014). “Chapter 70 – Lipolysis.” Textbook of Veterinary Physiological Chemistry (3rd Edition), Pages 444-449. Accessed 30 May 2018 from <https://www.sciencedirect.com/topics/neuroscience/lipolysis>

  • Fruhbeck, G et al. “Regulation of Adipocyte Lipolysis.” Nutr Res Rev. 2014 Jun; 27(1): 63-93. Doi: 10.1017/S095442241400002X



Lipolysis

Spindle Fibers

Spindle Fibers Definition


Spindle fibers are microscopic protein structures which help divide genetic material during cell division. The spindle fibers form out of the centrosome, also known as the microtubule-organizing center, or MTOC. Spindle fibers are formed from microtubules with many accessory proteins which help guide the process of genetic division. The spindle fibers form during cellular division near the poles of the dividing cell. As they extend across the cell, the search for the centromere of each chromosome.


Centrosome Cycle

Centrosome Cycle


Once attached, the spindle fiber is pulled back. With each fiber comes the chromosomes, which separates them along the poles. This process can be seen in the image above. The spindle fibers can be seen extending in all directions from the centrosomes. These spindle fibers are formed from several microtubules. The spindle fibers act like small machines during cell division. They carefully assemble and divide the chromosomes, and have been doing so for billions of year. But how does this complex process take place?


Structure of Spindle Fibers


The centrosome, or MTOC, always has some microtubules preassembled. On the surface of the MTOC are small proteins, responsible for lengthening or shortening the microtubules. These proteins respond to signals from the cell, and when it is time for cell division, the begin lengthening the spindle fibers. To do this, they must add subunits of alpha-tubulin and beta-tubulin. Together, these two small proteins form the structure of a microtubule. Many individual microtubules together are called spindle fibers. A single microtubule can be seen in the graphic below.


Microtubule structure

Microtubule structure


Functions of Spindle Fibers


Shrinkage and Growth


The main feature of microtubules, and therefore of spindle fibers, is that the proteins which control them can extend or contract the microtubule by adding or removing tubulin dimers. At first the MTOCs must add many of these dimers to the microtubule, to extend it across the cell. As the microtubule travels, it eventually reaches a chromosome. Special proteins within the centromere of the chromosome can attach to the microtubule. Here, there are also proteins which can shorten and extend the spindle fibers.


This is one of the main ways that the chromosomes get aligned on the metaphase plate, a hypothetical middle of the cell. It is also the main way they are separated during anaphase. While the addition and subtraction of dimers is one of the main ways that spindle fibers help carry chromosomes about the cell, there are two other primary methods.


Sliding


When spindle fibers from opposite poles of the cell meet, they are bound together by a special protein. Instead of grabbing onto a chromosome, they more or less attach to each other via the protein. This protein is a specialized motor protein, which reacts to signals from the cell. At the appropriate time during cell division, the motor protein will begin crawling along each microtubule it is attached to. This “sliding action” causes pressure to be exerted against the poles, and helps drive the poles apart. This action of the spindle fibers is what forces the cell apart and allows for it to be divided in half during telophase.


Microtubule anchors


The final action carried out by some spindle fibers is that of anchoring to the cell surface. On the inside surface of the cell membrane, specialized proteins are placed to anchor the microtubules. While these anchors cannot assemble dimers into the microtubule, they can bind onto it. Then, when the MTOC starts removing microtubule dimers, the whole spindle fiber shortens. In this way it pulls the cell membrane toward the MTOC, and starts to define the area of the newly forming cell.


Quiz


1. Which of the following is NOT caused by the actions of spindle fibers?
A. The movement of chromosomes
B. The change in shape of the cell
C. The structure of the cell when not dividing

Answer to Question #1
C is correct. Spindle fibers form during cell division and are disassembled afterwards. While there are many different kinds of microtubules, they only act as spindle fibers during cell division. After cell division, the function of structure is carried out by more interspersed microtubules and other small structures. By using a completely different set of proteins, cell division and the organization of spindle fibers which is required can be completely regulated.

2. Microtubules form in a peculiar fashion. While the entire structure is just repeated units of the small tubulin dimer, the structure has polarity to it. That is, each side of the microtubule is different. On one side the beta-tubulin is more exposed, while on the other side the alpha-tubulin is more exposed. How must the proteins in the MTOC and the proteins on chromosomes be different in order to work?
A. They must be the same
B. They must be able to add dimers from opposite sides
C. They are completely different processes, therefore they are completely different proteins

Answer to Question #2
B is correct. The different sides of the microtubule (often referred to as + and –), have slightly different shapes which are just the opposite of each other. On one side, the protein must add or remove dimers with the alpha-tubulin facing in, while the others must do it with the beta-tubulin facing in. These two dimers are almost identical, so the change is small. But, it is still present and affects the way the cell’s machinery works.

3. Often, when products of an organelle are exported, they are contained within vesicles. These small compartments of cell membrane are then attached to a microtubule via a small motor protein. The protein works its way down the microtubule, like in the sliding example above. It carries the vesicle to another organelle or the cell surface. Here it can be expelled or absorbed. Are these microtubules considered spindle fibers?
A. No
B. Yes
C. Maybe

Answer to Question #3
A is correct. These are definitely not spindle fibers. Remember that spindle fibers are formed only during cell division and that their main purpose is dividing the genetic components of the cell. These are microtubules, but there are many uses for microtubules within the cell.

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.

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

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



Spindle Fibers

Commensalism, Mutualism and Parasitism

Symbiosis describes several types of living arrangements between different species of organisms in an ecosystem. These relationships can be beneficial, neutral, or harmful to one or both organisms which are called symbionts. In the complex web of nature, species often have several symbiotic relationship at a time.


Symbiosis can take two forms known as obligatory and facultative. In obligatory symbiosis, one or both organisms are entirely dependent on the relationship and will die without it. Conversely, organisms in facultative relationships can live independently from each other.


Symbiotic relationships are also described by the physical relationship between the symbionts. Conjunctive symbiosis occurs when the symbionts have bodily contact with each other. In contrast, symbionts that do not have physical contact have a disjunctive symbiotic relationship. The term ectosymbiosis is when one organism lives on another, like a flea living in a dog’s fur. Endosymbiosis is a relationship where one symbiont lives in the tissues of another such as bacteria living in the human gut.


Commensalism, mutualism, and parasitism are the three main categories of symbiosis found in nature.


Commensalism


In a commensal relationship, one species benefits and there is a neutral effect on the other—it neither benefits nor is harmed. An example of this relationship is birds building nests in trees. The nests don’t interfere with photosynthesis and are light weight, so they don’t put a strain on the trees. The birds, on the other hand, benefit by having their young protected from predators on the ground and hidden by the leaves and branches of the tree. The tree may also provide an accessible food source for the birds such as berries, grubs, and insects. Other examples of commensalism are spiders spinning webs on plants and hermit crabs that use discarded snail shells to protect themselves.


Commensal relationships are sometimes hard to identify because it can be difficult proving that one symbiont does not benefit in some way from the relationship.


Mutualism


In this type of symbiosis, both organisms benefit from the relationship. A classic example of this is the relationship between termites and the protists that live in their gut. The protists digest the cellulose contained in the wood, releasing nutrients for the benefit of the termite. In turn, the protists receive a steady supply of food and live in a protected environment. The protists themselves also have a symbiotic relationship with the bacteria that live in their gut, without which they could not digest cellulose. This relationship between termites and protists is obligatory—the termites would die of starvation without the protists to digest their food.


Other examples of mutualism are the algae that live in the tissues of coral in reefs, clownfish that live in the tentacles of sea anemones, and the relationship between the Oxpecker bird and zebras and rhinoceroses on the African plains.


Parasitism


Parasitism is a relationship where one symbiont benefits (the parasite) and the other (the host) is harmed in some way and may eventually die. Parasites can damage their hosts or sicken them and make them weak. There is usually a built-in selection process that slows down the rate of damage to the host, giving the parasite time to complete its reproductive cycle and for its offspring to find a new host.


A tapeworm in the digestive tract of a human or other animal is an example of a parasitic relationship. The worm feeds on the food the person eats and grows within the intestines, sometimes reaching 50 feet in length. Other examples are the malaria parasite spread by mosquitoes, fleas and ticks, and aphids that suck the sap from plants.


References



  • Nelson, D. (2018, February 6). Mutualism, Commensalism, Parasitism: Types of Symbiosis with Examples. Retrieved May 23, 2018, from https://sciencetrends.com/comparing-examples-mutualism-commensalism-parasitism-symbiosis/

  • Symbiosis. (2018, May 9). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Symbiosis&oldid=840414702



Commensalism, Mutualism and Parasitism

Sperm Motility

Sperm motility is the ability of sperm to move through water during external fertilization or within the female reproductive tract for internal fertilization to reach the egg. Motility also refers to the quality of the sperm motion, meaning that sperm which does not move properly can’t reach the egg and successfully fertilize it. Motility also encompasses the ability of the sperm to penetrate the egg once it reaches it.


Sperm Structure and Movement


A sperm has four main sections: the head, midpiece, tail, and end piece (Figure 1). The head contains the nucleus and is surrounded by the acrosome (cap) and the plasma membrane. The acrosome contains the enzymes the sperm will need to penetrate the surface of the egg. The centriole (which the sperm will donate to the egg upon fertilization) joins the head to the midpiece which has a filamentous core composed of 11 tubules called the axoneme. The midpiece is surrounded by mitochondria that supply energy for the sperm in the form of adenosine triphosphate (ATP).


The tail or flagellum of the sperm is the longest section and the terminal disc separates it from the midpiece. The tail, powered by ATP made by the mitochondria in the midpiece, propels the sperm using a back and forth lashing motion. The motion is created by the rhythmical sliding of the tubules in the axoneme. The end piece contains the axoneme surrounded by the plasma membrane. It is located at the terminus of the tail and tapers down in diameter.


Changes in ion concentration and pH activate sperm movement and the requirements vary by species. For example, in some mammals, an increase in pH and calcium ions activates sperm. The ultimate effect is membrane hyperpolarization which activates the sperm.


Human spermatozoa diagram

Figure 1


The image above shows the detailed structure of a human sperm cell.


Evaluating Sperm Motility


The percentage of motile sperm is the most widely used measurement of semen quality. Normal or acceptable sperm motility varies among species. For example, human sperm motility greater than 50% is normal but only 30% is required in bulls, and as high as 70% is required in dogs. Sperm motility is described as non-motile, progressively motile, and non-progressively motile. Progressively motile sperm swim in a straight line while non-progressively motile means the sperm swim in an abnormal path such as around in circles. Test results usually report the percentage of progressively motile sperm.


There are three main methods for quantifying sperm motility. Some are more accurate than others and require more skill on the part of the operator and/or use more expensive equipment. In a manual motility estimate, a diluted sample of semen is placed on a pre-warmed slide and viewed under a microscope. The operator counts the number of non-motile, progressively motile, and non-progressively motile sperm in at least ten different fields on the slide. From this, an estimate of the percentage of motile sperm is calculated.


Track motility estimates use the same sample preparation as the manual motility estimate. The sperm are photographed using an exposure time of about 0.2 seconds which records their movement on the slide. Progressively motile sperm will leave tracks in a straight line and the non-progressively motile sperm will leave circles or tracks showing some other abnormal path of movement. Of course, non-motile sperm leaves no tracks.


The latest technology involves computer-aided motility analysis. The method is similar to the track motility test, but software detects and tracks the movement of each sperm in the sample and tabulates the data automatically. This method gathers additional data such as the velocity of the sperm and other details about their movement.


References



  • Sperm. (2018, May 15). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Sperm&oldid=841448719

  • Sperm motility. (2017, August 5). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Sperm_motility&oldid=793978230

  • Sperm Motility. (n.d.). Retrieved May 22, 2018, from http://www.vivo.colostate.edu/hbooks/pathphys/reprod/semeneval/motility.html



Sperm Motility

Monocot Root, Leaf, Flower and Plants

The term monocot is short for monocotyledon. The cotyledon is an embryonic leaf in a seed that is the first to emerge when it germinates. Monocot seeds have one cotyledon while dicotyledons, or dicots, have two. Monocots and dicots are two types of angiosperm plants which reproduce using seeds and fruits.


There are about 60,000 species of monocot plants. The largest family are the orchids which have over 20,000 species followed by grasses with 10,000 species. Scientists believe monocots evolved as early as 140 million years ago. Based on pollen grains in the fossil record, the earliest monocots lived in the early Cretaceous period about 120-110 million years ago.


Monocots are found in a variety of habitats. They grow primarily on land but also in rivers, lakes, and ponds, mostly rooted to the bottom but sometimes free-floating. Some also live in intertidal zones near the seashore and a few are marine plants rooted in shallow areas in the ocean.


Roots


The roots of monocots cannot grow in diameter due to the lack of vascular cambium. Instead, they grow more roots at the shoot (radicle) and send out creeping shoots called runners or rhizomes (Figure 1). The coleorhiza is a tough sheath of tissue at the end of each root that protects it as it works its way through the soil. A structure called the coleoptile has the same function earlier in the growth of the root. This fibrous root system that originates from areas of the plant other than existing roots is called an adventitious root system.


The tissue at the center of monocot roots consists of xylem and phloem (vascular bundle) and it is surrounded by the cortex which is made of parenchyma cells (Figure 2). The outermost layer of the root is called the epidermis followed by the exodermis or sclerenchyma. The endodermis is an inner layer of cells surrounding the vascular bundle. The endodermis and phloem are separated by a layer of cells called the pericycle where root branching occurs.


Figure 1

Figure 1


The image above shows the root structure of a germinating monocot seed.


Figure 2

Figure 2


The image above is the cross section of a monocot root.


Leaves


Monocot leaves are usually long and narrow or oblong with parallel veins running through them (Figure 3). However, the diversity of nature reveals many exceptions to this rule. There is usually one leaf per node on the stem because the base of the leaf takes up more than half of the circumference of the stem.


Monocot leaves have an equal number of stomata (pores) on the upper and lower leaf surfaces. They also have large vascular bundles and bulliform (bubble-shaped) cells on the upper surface. Both of these features help monocots retain water during dry or stressful environmental conditions. Also, the cuticle layer is thicker on the upper leaf surface.


Philodendron Wilsonii

Figure 3


The image above shows the parallel veins in Philodendron wilsonii which is characteristic of monocots.


Flowers


Monocots are identified by their flowers and flower parts that are in groups of three, also called trimerous (Figure 4). About two-thirds of all monocots are pollinated by animals including bats, monkeys, deer, rodents, and birds such as hummingbirds. Therefore, the flowers are often colorful and ‘showy’ to visually attract pollinators and they use pleasing aromas for chemical attraction.


Ornithogalum umbellatum

Figure 4


The image above shows the grass lily Ornithogalum umbellatum with its flower parts in multiples of three, characteristic of monocots.


Examples of Monocot Plants


Monocots are important plants around the world both economically and culturally. They account for many human and animal food staples like wheat, corn (Figure 5), barley, rice, and grasses. Other examples of monocot plants are bananas, sugarcane, palms, pineapples, orchids, and lilies. Monocots make up the most species grown in agriculture in terms of the amount of biomass produced.


References



  • Monocotyledon. (2018, May 16). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Monocotyledon&oldid=841518727

  • Monocotyledon plant. (n.d.). Retrieved May 22, 2018, from https://www.britannica.com/plant/monocotyledon



Monocot Root, Leaf, Flower and Plants

Monocot vs Dicot

Angiosperms are plants that live on land and reproduce using seeds in flowers and fruits.


Monocotyledons and dicotyledons, also known as monocots and dicots, respectively, are two types of angiosperm plants. The Italian physician and biologist Marcello Malpighi (1628 – 1694) was the first to use the term cotyledon (the Latin word meaning seed leaf) and John Ray (1627 – 1705), an English naturalist, was the first to notice that some plants have one cotyledon and others have two.


The cotyledon part of angiosperms is an embryonic leaf that is the first leaf (or leaves) to appear when a seed is germinating. Cotyledons perform photosynthesis but are not true leaves because they are present in the seed before it germinates. True leaves grow after the seed has germinated. Cotyledons may last only a few days after the seed germinates (ephemeral) or last up to a year (persistent).


Monocots and dicots differ in several ways which help in their identification and understanding of their origins. Paleobotanists, scientists who study the origins of plants, hypothesize that dicotyledons evolved first, and monocots branched off about 140 to 150 million years ago either from the fusion of the cotyledons or as a separate line. See Figures 1 and 2 for illustrations of the different physical features discussed below.


Monocots


Monocot plants have one cotyledon. They also have long narrow leaves with parallel veins. Cutting a cross section from the stem of a monocot shows the vascular bundles scattered around in the plant tissue. The young plant stores food in the form of starches and other nutrients in a structure called the endosperm.


Another key characteristic for identifying monocots is by the number of flowers or flower parts which are arranged in groups of three. Also, the pollen grains of monocot plants have a single pore or furrow making them monosulcate (from the Greek word mono meaning ‘single’ or ‘one‘ and the Latin word sulcatus meaning ‘furrow’) and new roots originate from the stem of the plant. Some examples of monocots are lilies, orchids, corn, rice, wheat, barley, pineapple, sugar cane, bananas, palms, and grasses.


Dicots


As opposed to monocots, dicots (also called eudicots) have two cotyledons during germination which supply the young plant with food and nutrients. The leaves of dicot plants come in a variety of shapes and sizes and the veins form branching patterns. Microscopic examination of dicot seeds shows a structure called the hilum which is a scar on the seed coat where the ovary was attached. This feature is not seen in monocots. Also, different from monocots is the roots of dicot plants originate from the radicle.


Another way dicots are distinct from monocots is their flowers and flower parts are arranged in multiples of four or five. In addition, the cross section of a dicot stem shows the vascular bundles arranged in a circular pattern. Unlike monocots, the pollen grains of dicot plants have three pores and are called trisulcate. Dicot plants can also have bark and secondary growth increases the diameter (girth) of the plant. Examples of dicots include potatoes, tomatoes, apples, pears, peaches, cauliflower, peppers, broccoli, and cabbage.







































MonocotsDicots
Direction of leaf veinsParallelBranched
Orientation of vascular bundlesScatteredArranged in circles
Number of flowersMultiples of 3Multiples of 4 or 5
Number of embryonic leaves12
Origin of new rootsFrom nodes in the stemFrom the radicle
Shape of true leavesMostly long and narrowWide variety of shapes
Secondary growthNoneYes. Plant girth increases each year
Forms true bark?NoYes
Number of furrows or pores in pollen grains1 (monosulcate)3 (trisulcate)
Food and nutrient storage locationEndospermCotyledons
Has a hilum?NoYes

Monocot dicot seed

Figure 1: The image above shows a generalized dicot seed (1) and a generalized monocot seed (2). The structures in each type of seed are: A = seed coat, B = cotyledon, C = hilum, D = plumule, E = radicle, and F = endosperm. Note that the dicot seed lacks endosperm, and the monocot does not have the hilum that is present in the dicot seed.


Dicot stem vs monocot stem

Figure 2: The image above shows a cross section of the stem of a dicot plant (left) and monocot (right). Note how the vascular bundles are scattered in the monocot stem and arranged in a circular pattern in the dicot stem.


References



  • Cotyledon. (2018, April 6). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Cotyledon&oldid=834509052

  • OpenStax College. (2018). Concepts of Biology. Houston, TX. OpenStax CNX. Retrieved from http://cnx.org/contents/b3c1e1d2-839c-42b0-a314-e119a8aafbdd@9.39



Monocot vs Dicot

Lateral Meristem

Meristem is undifferentiated plant tissue found in areas of plant growth. The three types of meristematic tissue are intercalary, apical, and lateral. Apical meristem tissue is found in the tips of shoots and gives rise to leaves and flowers and is also found in the roots. The intercalary tissue in the middle of the plant is capable of rapid growth and regrowth. For example, the intercalary tissue at the base of a blade of grass allows it to regrow after being cut.


Plants use lateral meristem tissue to grow in diameter as part of secondary growth. There are two types of lateral meristematic tissue—the vascular cambium and the cork cambium.


Vascular Cambium


In plants, the vascular cambium is the main route by which the stems and roots grow. The tissue consists of xylem toward the outside and phloem inside. In woody plants, it forms a continuous ring of new wood around the stem. Herbaceous plants don’t have wood, so the vascular cambium forms bead-like bundles that create a ring around the stem. The two types of vascular cambium cells are fusiform initials which are tall and aligned with the axis of the stem and ray initials which are smaller than fusiform initials and rounder.


The vascular cambium has its own set of hormones that control growth, regulation, and maintenance activities in the tissue. The hormones belong to such families as auxins, gibberellins, and cytokinins, and chemicals like ethylene also have hormonal functions in the vascular cambium.


Xylem rays

The image above is the cross-section of a plant stem showing the vascular cambium, xylem cells, and xylem rays.


Cork Cambium


This tissue is present in mostly woody and some herbaceous plants and gives rise to the cork or bark layer on the outside of the stem and secondary growth in the epidermis of roots. This is accomplished by replacing the epidermal cells with the periderm which consists of three layers. The phelloderm is the innermost layer made of living parenchymal cells. On top of that layer is the cork cambium itself or the phellogen that gives rise to the periderm. The outermost layer is the cork or phellem (bark) which is made of dead, air-filled cork cells. The development and appearance of the cork cambium varies greatly among species. Some plants and trees have smooth bark while others are rough, scaly, and even naturally flake off from the tree.


Cork cambium

In the image above, the black pointer shows the location of the cork cambium in the cross-section of a woody plant stem.


References



  • Cork cambium. (2018, January 30). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Cork_cambium&oldid=823080623

  • Vascular cambium. (2018, March 2). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Vascular_cambium&oldid=828437156



Lateral Meristem

Marine Ecosystem Facts

Marine ecosystems include not just the oceans but also shorelines, tidepools, estuaries, barrier islands, mangrove forests, and salt marshes. Here are the top 5 facts about marine ecosystem.


The Marine Ecosystem is the Largest Ecosystem on Earth


The oceans alone cover about 70% of the Earth’s surface or 140,000,000 square miles. The average ocean depth is about 12,000 feet and the deepest point is the Mariana Trench in the Pacific Ocean with a depth of about 32,800 feet.


The Marine Ecosystem has the Greatest Biodiversity on Earth


Almost half of the known species on Earth live in marine ecosystems and scientists suspect there may be another 1 million yet to be discovered. Roughly 700,000 to 1 million species live in the oceans.


Phytoplankton in the Oceans Provide 50% to 85% of the Oxygen on Earth


Phytoplankton are tiny plants that live in the upper areas of the ocean and use photosynthesis to make their food. They are so abundant in the oceans that all together they account for about 50% of the photosynthetic activity and over 50% of the oxygen production on the planet.


Mangrove Forests are Diverse Ecosystems


Mangrove forests are found on tropical and subtropical marine coastlines and tidal areas. They contain small trees and shrubs tolerant of salt water. The root systems of the forests form tangled webs of habitat where many species of fish, invertebrates, seabirds, and waterfowl live, reproduce, and mature.


Oceans Regulate the Earth’s Climate


The oceans absorb most of the heat radiated from the sun especially around the equator. The ocean currents distribute the heat around the planet, but most of the heat is lost due to evaporation. The constantly evaporating ocean waters create rain, thunderstorms, and hurricanes by increasing the temperature and humidity of the air. Because the trade winds carry these storms over vast distances, most of the precipitation that falls on land originates in the oceans.


General characteristics of a large marine ecosystem

The image above shows the typical characteristics of the marine ecosystem in the Gulf of Alaska.


References



  • Facts and figures on marine biodiversity | United Nations Educational, Scientific and Cultural Organization. (n.d.). Retrieved May 16, 2018, from http://www.unesco.org/new/en/natural-sciences/ioc-oceans/focus-areas/rio-20-ocean/blueprint-for-the-future-we-want/marine-biodiversity/facts-and-figures-on-marine-biodiversity/

  • Ocean. (2018, May 15). In Wikipedia. Retrieved from https://en.wikipedia.org/w/index.php?title=Ocean&oldid=841293100



Marine Ecosystem Facts

How Climate Change Affects the Biodiversity of Marine Ecosystems

The biodiversity found in marine ecosystems is greater than in any other on Earth. Climate change causes wide-ranging effects including changes to water pH, nutrients, oxygen content, and stratification. These changes affect the biodiversity of communities, particularly in the polar regions of the planet.


Effects on Ice-Dominated Polar Ecosystems


Climate change is affecting the Earth’s northern and southern poles at a faster rate than anywhere else. The health of polar marine ecosystems is intimately tied to seawater temperature and the amount of sea ice present. These two factors influence the growth and reproduction of organisms, food sources, and the biogeochemical cycles of the region.


An example of the effects of climate change on the biodiversity in the polar regions is the reduced population of Adélie penguins. The loss of sea ice in the area along with reduced amounts of krill and an increase in late spring snowfalls has resulted in an 80% reduction in the Adélie penguin population in the region of Palmer Station in Antarctica. At the same time, species such as the Gentoo penguin and fur seals are migrating to this area to take advantage of the ecological niche that has opened up due to the decline in the penguin population.


Effects on Coral Reef Ecosystems


About 25% of all marine species are associated with coral reefs. These reefs are very sensitive to changes in the pH and temperature of ocean waters. For example, an increase in water temperature as little as 1°C causes coral bleaching, the loss of color due to the death of the zooxanthellae that live within the coral tissues. But, bleaching does not affect only the color of coral. Moderately bleached coral has lower growth and reproduction rates and severe bleaching kills them. Because of this high sensitivity, reef stress is an early warning sign of changes in water acidification and temperature. Besides climate change, coral reefs also suffer from pollution, overfishing, invasive species, and nutrient overenrichment.


Many organisms that live in coral reefs are negatively impacted when reefs are damaged by increased temperature and water acidification. Coral provides food, structure, mating/spawning areas, and cover for these creatures. With the loss of reefs, some species can migrate to rocky areas to live but others specialized to live in the reefs will die off. Scientists believe if conditions continue to deteriorate, there will be reduced diversity of fish and invertebrate species in these areas.


Estimated change in annual mean sea surface pH

The image above shows the change (delta) in the surface water pH of the world’s oceans. The acidification of the oceans is one of the key indicators of climate change.


References



  • Doney, S. C., Ruckelshaus, M., Duffy, J. E., Barry, J. P., Chan, F., English, C. A., … Talley, L. D. (2012). Climate Change Impacts on Marine Ecosystems. Annual Review of Marine Science, 4(1), 11–37. https://doi.org/10.1146/annurev-marine-041911-111611



How Climate Change Affects the Biodiversity of Marine Ecosystems