Buffon

buffon_1707-1788George-Louis Leclerc, Comte de Buffon was a French naturalist during the period of the French Enlightenment. He studied at a Jesuit school where he showed a proficiency for mathematics. He is also considered one of the founders of Paleontology.

Buffon was skeptical of the classification system of Linnaeus, the famous naturalist. He particularly disagreed with the idea of grouping animal species into families. Buffon believed that the earth was formed from a piece of the sun that was torn off, and that the moon was torn off from the earth by centrifugal force. The age of the earth was estimated to be around 75,000 years which was a considerable figure since the prevailing theory of the creation of the world ranged from about 4000 to 6000 BC. He changed his estimation to 3,000,000 years but he retraced it for fear of being misunderstood.

He thought that all animals sprung from common ancestors over great periods of time. The quadrupeds, Buffon said, sprang from 13 original species that were present from nearly the beginning. These 13 all sprang spontaneously as soon as organic molecules appeared. According to Buffon, most of these species disappeared, adapting and changing in accordance to the change in their environment. He explained that the reason large creatures have little variation is because they reproduce slowly. Likewise, the reason that small mammals and birds have so many types is because they are reproduce prolifically.

Buffon also studied the human species, determining that the distinguishing characteristic of man is reason. According to Buffon, reason stemmed from language, and language stemmed from society. Society, he said, was necessary because, unlike other species, man requires a great deal of nurturing and upbringing. Elephants, the most intelligent of the animals, are as such because they have a form of society. He also said that the very first humans had black skin, and that humans and animals have the same origins.

Theology and religion were completely absent from his studies, even though three of his brothers went into the Church and two of whom became distinguished. Buffon was an interesting if not extremely important scientist of the French enlightenment, and it is interesting to read his theories and to follow his reasoning, even if it was false.

Essay 16: Aquatic Osmoregulators

Aquatic animals have several mechanisms for dealing with the effects of osmosis. Without these methods, the cells within these creatures would either shrivel up and die, or swell up and explode. Osmosis is the tendency for a liquid (solvent) with a low concentration of particles (solutes) dissolved in it to move to through a semi-permeable membrane to an area of high solute concentration. The semi-permeable membrane allows the solvent to pass though, while blocking the solutes. The area on the side of the membrane with a higher concentration of solutes is called the hyperosmotic side, and the side with lower solute concentration is called the hypoosmotic side. Osmosis is necessary for the function of the kidneys, which rely on its properties to remove toxins from the blood, and for the re-absorption of water.

Osmosis presents a problem to aquatic life, because through it the concentration of water (H2O, the solvent) or salt (NaCl, the solute) can be affected in dangerous ways. In salt water, the cells of an aquatic animal are hypoosmotic in relation to the surrounding water, so through osmosis water has the tendency to pass through the cell membrane and leave the cell. This causes problems, because water is essential for the function of a cell. Likewise, in a freshwater environment, the interior of cells are hyperosmotic in relation to their surrounding water. Through osmosis, water tends to leave the area of lower solute concentration, and enter the cells. This can also be a problem, because too much water can cause a cell to explode (cytolysis).

In aquatic animals, there are several different methods employed to maintain osmotic homeostasis. Most marine invertebrates are osmoconformers, meaning that they maintain the concentration of solutes in their own body to conform with that of their environment. The downside of this is that it is dependent on a stable water composition.

The next group are the osmoregulators, who regulate the concentration of solutes and solvents in their cells. There are two different kinds of osmoregulators: marine osmoregulators and freshwater osmoregulators. Marine osmoregulators have to deal with high solute concentration in their environment, and a constant tendency to lose water. To cope they drink large amounts of water and use active transport (that which is not caused by a natural tendency, but by expending energy) to remove chloride ions (and subsequently sodium ions) from their body. Freshwater osmoregulators have the opposite problem, which is too much water. They drink very little water, and excrete lots of water in their urine, while obtaining new salts and minerals from food.

Salmon are an interesting case, because they spend most of their life in salt water and return to freshwater later on. When in freshwater, they function as regular freshwater osmoregulators, but they need to deal with extra salt in the ocean. In order to cope, they secrete the steroid hormone cortisol, which stimulates chloride cells to grow. These chloride cells secrete salt out of the body, and maintain osmotic homeostasis.

In order to live in different environments, different animals have different methods for keeping the concentration of water and salts in their bodies at an optimal level. These methods used include osmoconformity, and marine and freshwater osmoregulation. Osmosis can be either a problem that needs to be solved, or a necessary property that functions as a tool, especially in the kidneys. Whatever the case, creation has many ways of correcting for it, and even harnessing it.

Essay 15: On the Counter-Current Exchange

For animals with gills, such as fish, the processes of gas exchange (extracting oxygen and expelling carbon dioxide) are more difficult to accomplish than for terrestrial creatures with lungs. The reason for this is that gases always flow from an area of high concentration to an area of lower concentration. On land, there is a much higher concentration of oxygen in the air than in water, so oxygen in the air naturally wants to go into the blood. With water, however, there is a much lower concentration of oxygen, so gas exchange is much more difficult. The gills of fish have to be very efficient at extracting oxygen from the water, so they employ something called the counter-current exchange.

The gills are comprised of folds of filaments that are rich in capillaries. Blood that is low in oxygen passes through the capillaries, and gets replenished. The blood flowing through the gills flows in the opposite direction from the water that passes over them. This enables a much more efficient method of extracting oxygen because the water is always encountering blood of a lower oxygen content, and likewise the blood is always encountering incoming water of a higher oxygen content. If the blood and water were flowing in the same direction always, then the blood would be encountering water of a progressively lower oxygen content, leading to a very inefficient system. The very simple configuration that allows for counter-current exchange enables fish and other aquatic animals with gills to get the most possible amount of oxygen, and live more efficient and active lives.

Essay 14: On Hormones Involved in Hunger and Satiety

The feelings of hunger and satiety are the direct result of hormones and cell-signalling. There are four major hormones involved appetite: insulin, leptin, ghrelin, and PYY.

Insulin suppresses appetite, and is released by the pancreas when the blood sugar reaches a certain threshold. Leptin also suppresses appetite, but is released by fat tissue. The burning of fat cells lowers leptin levels in the body, increasing appetite. From this it would seem that among the obese, there is very little appetite, which is often not the case. One possible reason for appetite to be retained even in the presence of more fat tissue than average is that with larger and larger concentrations of leptin, cells experience what is known as desensitization, and become less influenced by it. Ghrelin is sometimes known as the hunger hormone, and increases the appetite. Its release is triggered when the stomach is empty, and is stopped when the stomach is stretched. PYY stands for peptide YY, and is a short peptide that operates by counteracting the effects of ghrelin. It is secreted by the small intestine after a meal.

Cell signalling plays an important role in controlling appetite. The presence or absence of certain hormone directly influences whether someone is hungry or full. Without these hormones to limit the amount of food we eat, we would simply eat until we ruptured our stomachs.

Essay 13: On Amniotes

The reason that reptiles, birds, and even mammals are able to live terrestrial lives is due to the fact that they are all amniotes, that is, they all produce an amniotic egg. Fish and amphibians are not able to be born on land because they require lots of moisture, which they get directly from the water that surrounds them. Amniotes have overcome this limitation with the amniotic egg.

Amniotes are all tetrapods that exhibit an amniotic egg. The amniotic egg is named for the amnion, which is a fluid filled sac that completely surrounds the developing embryo. It protects the embryo, and allows it to be supplied with the moisture it needs without being in direct contact with water. This major development has allowed organisms to become completely terrestrial.

Other structures in the amniotic egg, called the extraembryonic membranes, include the yolk sac, the chorion, the allantois, and of course, the amnion. The yolk sac is the source of nutrients in the amniotic egg, supplying them to the embryo through blood vessels. The chorion is a membrane that allows gases to be exchanged. It retains moisture, while allowing oxygen and carbon dioxide to cross it. The allantois is the embryo’s waste storage system. It stores metabolic wastes, while also exchanging gasses with the chorion.

At first glance, mammals do not seem to be amniotes, because they do not lay eggs, with the exception of the monotremes (platypuses and echidnas). However, mammals are indeed amniotes, because the amniotic egg which they produce remains inside of the body. All mammalian embryos have an amnion and a chorion, while the allantois is incorporated into the umbilical cord; and the yolk sac cells develop into the embryo’s blood cells, and then migrate into the embryo. Most reptile and bird eggs develop a shell, which seals in moisture and protects the egg while allowing gas exchange; and an albumen, which stores additional nutrients. Most mammals (again except the monotremes) lack a shell and an albumen.

The amniotic egg has allowed animals to colonize land, and even become completely terrestrial, as is usually the case. It may seem like mammals are not amniotes, but they share all the important characteristics that define them as such.

Essay 12: On Possible Uses of Scorpion Venom

Scorpions are Arachnids belonging to the order Scorpiones. Of the 1,750 known species, only 25 are capable of killing a human being. This may still seem like a lot, but many of these would only kill the very young and the very old. Their venom is a cocktail of various neurotoxins and enzyme inhibitors, designed for a wide variety of victims. Despite the obvious dangers of scorpion venom, there are possible human uses which may pose great benefits for mankind.

Chlorotoxin, a 36-amino acid peptide found in Leiurus quinquestriatus (the Deathstalker scorpion), has the potential to treat cancerous tumors, because it binds with glioma (tumor) cells. Maurotoxin, a 34-amino acid peptide of Scorpio maurus (the large clawed scorpion), may be able to treat certain autoimmune diseases as an immunosuppressant, such as rheumatoid arthritis, inflamatory bowel disease, and multiple sclerosis. Meucin-13 and meucin-18, found in Mesobuthus eupeus (the lesser Asian scorpion), destroy microbes, such as bacteria, fungi, and yeasts by a process known as cytolysis, in which cells literally explode due to an osmotic imbalance within the them. Meucin-24 and meucin-25, also from Mesobuthus eupeus, both target two different types of malaria parasites, those that attack rodents (Plasmodium berghei), and those that attack people (Plasmodium falciparum).

Scorpions are dangerous creatures, and should be respected. However, certain toxins in scorpion venom have the potential to be highly beneficial. One day they may widely treat cancer, autoimmune diseases, and malaria.

Essay 11: On Important Chordate Body Structures

Multicellular organisms, especially chordates (most vertebrates), exhibit several different body structures which allow for more sophisticated locomotion, sensory perception, and structure than in less developed animals.

All chordates exhibit a notochord, which is a long, flexible rod that provides support, and a place for muscles push against in locomotion. The notochord is present in the embryonic stage of vertebrates such as mammals, and develops into spinal discs later on. Another important development is the muscular tail. It is important as a source of locomotion in marine chordates, and serves many purposes in terrestrial chordates. The muscular tail is significant because it extends beyond the digestive tract. This is important because a combination of the various delicate digestive organs and the constant movement involved in locomotion would result in an efficiency loss of both systems.

Finally, another important chordate innovation is the pharyngeal cleft. The pharyngeal clefts are located on the pharynx, the region of neck or head just behind the mouth. These clefts, or pouches, serve many purposes among the chordates. In fish and some amphibians, they develop into gills. In other aquatic animals, they may develop into filter-feeding mechanisms. In many terrestrial chordates, they develop into structures which aid in sensory perception, such as ears and other structures on the pharynx.

Chordates have many developments which allow them to surpass other animals on many levels. They can achieve more advanced locomotion and greater structural strength with the notochord and the muscular tail. They can develop specialized organs on the pharynx that aid in many systems out of the pharyngeal clefts. Chordates are advanced animals whose success is based on seemingly simple innovations.

Essay 10: On Sugar from Source to Sink through the Phloem

Sugar flows from source to sink in plants through a vital network of specialized tubes. There are sugar sources which also act as sinks, and sinks which act as sources.

A sugar source is anything that produces more sugar than it uses. Generally, the biggest sugar source in plants are the leaves, which convert water, CO2, and sunlight into sugar through photosynthesis. There are, however, other sugar sources in plants. The roots and storage organs of a plant may be used to to store starch, which can be broken down into sugar later.

Sugar sinks are anything that use more sugar than they produce. The main sugar sinks of a plant are growing tissue such as stems, roots, buds, and, counter-intuitively, young leaves. Storage organs like bulbs and tubers can also be sinks, when they absorb sugars for later use.

Sugar moves from source to sink through a network of vascular tissue. There are two different kinds of vascular tissue, called the xylem and the phloem. The xylem transports a thin solution of water and minerals up from the roots, called the xylem sap. The phloem transports a thick syrup-like solution of various large molecules, amino acids, and sugars, called the phloem sap. The phloem sap is pushed from source to sink, because there is a higher concentration at its source. Plants are able to cut off sugar supply to fruits, flowers, and other non-vital organs in times of scarcity to supply the vital organs.

It has been suggested that the phloem serves as a sort of primitive nervous system in plants. In addition to transporting sugars, the phloem also transports molecules used in cell signaling. The phloem is similar to the circulatory and nervous system in animals.

Some sugar sources, such as leaves, can also be sinks when they are young and still growing. Likewise, sugar sinks, like roots and storage organs, can also be sources when sugar is scarce. Sugar moves from source to sink through a vital system of vascular tissue called the phloem, which acts like a primitive nervous system as well. The phloem is a vital part of vascular plants which serves multiple purposes.

Essay 9: On Fruit

Fruits are very useful tools that aid plants in reproduction. They are also a major food source for many organisms. They may be very costly for  the plant to produce, but they are worth it.

Fruits are structures produced by angiosperms that are formed from the ovaries of flowers and that bear seeds. There are four different classifications of fruit; simple fruit, aggregate fruit, accessory fruit, and fruits which exhibit inflorescence. Simple fruit are comprised of a single carpel, or several fused carpels (a flower part which houses the ovaries), like blueberries. Aggregate fruit are formed from a single flower sporting many carpels, such as blackberries. Accessory fruit, or false fruit, are formed not from the carpel, but from accessory tissue outside of the carpel called the receptacle, like apples and pears. Fruits which are inflorescent are formed from several flowers that have fused together, forming one fruit, such as pineapples.

Fruits allow plants to widely disperse their seeds. They may be eaten be an animal and spread seeds through the animal’s feces. Fruits (like the ”helicopters” of maple trees) may develop wing-like appendages that allow them to glide away. Some fruits may have small hooks or bristles that allow them to attach themselves to animals and travel with them. There is also a process called dehiscence in which a mature fruit breaks open to release the seeds. These seeds may then be transported to other areas by wind or water. There is a variation on this process known as explosive dehiscence in which the fruit blows up and shoots seeds in all directions. There are many different types of fruit, and many methods of seed dispersal .

Fruits are very costly for plants to produce. They require lots of nutrients, and tons of energy. However, they do achieve their goal of dispersing seeds, whether by the digestive system of animals, by using wings to fly away, or by explosive force. Fruits may be expensive, but they are worth it.

Essay 8: On the Importance of Light in the Calvin Cycle

There are two processes involved in photosynthesis, which are the light-dependent reactions, and the light-independent reactions. Despite its name, however, the light-independent reactions are in fact indirectly dependent on light.

As their name implies, the light-dependent reactions are dependent on light. Basically,  light strikes a light harvesting complex which releases an electron. This electron is eventually passed to a chlorophyll a molecule, which reduces a primary electron acceptor, which starts several more reactions. These reactions produce O2, NADPH, and ATP.

Next comes the light-independent reactions, or the Calvin cycle. First, CO2 is attached to ribulose biphosphate, or RuBp. The resulting molecule is unstable, and breaks in two, forming two molecules of 3-phosphoglycerate, or PGA. ATP adds a phosphate group to each PGA molecule, creating glyceraldehyde 3-phosphate (G3P), which is further refined into sugar and carbohydrates.

The Calvin cycle produces sugar and carbohydrates, but it requires other molecules for it to work. It needs O2, NADPH, and ATP, all of which are supplied by the light-dependent reactions. So the Calvin cycle is dependent on the light-dependent reactions.