A small co-op of young farmers decided to grow organic corn. Corn is a crop that requires a lot of nitrogen. Growing corn removes a lot of nitrogen from the soil. Inorganic fertilizer contains nitrogen. It can be added to the soil to increase nitrogen levels. Inorganic fertilizers cannot be used for organic farming. The farmers must find another way to add nitrogen to the soil.

Why do the farmers care about nitrogen in soil? Nitrogen is needed by all organisms. Plants need nitrogen to grow and reproduce. Animals get nitrogen by eating plants or other animals. Nitrogen is used to form important molecules like amino acids, proteins, DNA, and RNA.

The air around us has a large amount of nitrogen gas. Plants cannot use nitrogen gas from the air. How does nitrogen gas in the air turn into the form that plants can use? The nitrogen cycle moves nitrogen from the air to organisms. Nitrogen is also returned to the air. The nitrogen cycle is a biogeochemical cycle. In this cycle atoms move between living and nonliving factors. Living factors in the nitrogen cycle are bacteria, plants, and animals. Nonliving factors are the air, bodies of water, and soil.

Nitrogen gas in the air is absorbed by soil and bodies of water. There are certain bacteria that can turn nitrogen gas into a useful form. Plants and algae use this nitrogen. The bacteria can be found in soil, root nodules, and bodies of water.

Plants that have nodules on their roots are called legumes. Bacteria live in the root nodules. The bacteria in the nodules add useful nitrogen to the soil. Legumes are rich in nitrogen. The organic farmers will use legumes to add nitrogen to the soil. Alfalfa, beans, and peas are all legumes.  Alfalfa is a legume with very deep roots and many nodules. These factors cause alfalfa to be nitrogen rich.  The farmers will use alfalfa to replace the nitrogen in the soil that is lost to the corn. The farmers will plant corn one season and alfalfa the next. They will continue to rotate the crops from one season to the next. The corn will remove nitrogen from the soil.The alfalfa will add nitrogen to the soil.  This crop rotation will keep proper nitrogen levels in the soil.

After harvesting crops, organic farmers plow leftover plant scraps into the soil. The scraps are allowed to naturally break down and decompose. There are special bacteria in the soil called decomposers. They change the nitrogen in the dead matter and wastes to a usable form. This is a natural source of nitrogen in the soil. It can be used by the next crop.

Nitrogen is returned to the air to complete the nitrogen cycle.  There are special bacteria that change useful nitrogen into nitrogen gas.  The bacteria are found mainly in soggy soil.  They are also found in soil at the bottom of oceans, lakes, and swamps.  The nitrogen gas formed by the bacteria is released back to the air.  The nitrogen gas in the air can be used in the nitrogen cycle again.

Organic farming should not harm the environment. Organic farmers know that disturbing the nitrogen cycle can cause harm. They do not use inorganic fertilizer because it greatly increases the amount of nitrogen in the soil. Extra nitrogen in soil is carried by runoff water. 

This water flows into local rivers, streams, lakes, and ponds. The extra nitrogen causes too many algae to grow. Large amounts of algae use up most of the oxygen in the water. The low oxygen levels can create a dead zone. Aquatic organisms cannot survive in a dead zone.

Nitrogen is a building block of all living things. Atoms of nitrogen move between living and non-living components of ecosystems. Nitrogen moves from the atmosphere to soil and water. Nitrogen moves through bacteria, producers, and consumers. It returns to soil and water, then back to the atmosphere. This nitrogen cycle allows atoms of nitrogen to be recycled repeatedly throughout different parts of the earth.

A student group was standing in front of a dinosaur exhibit at the Natural Science Museum. Their museum guide held up a small piece of natural chalk. The guide asked if anyone could explain how the piece of chalk could contain carbon that was exhaled by a dinosaur. The students talk about the facts needed to answer the question. First, they must find out where chalk is found in nature. Next, they must investigate the processes that provide a path for carbon in the air to become carbon in the chalk. The museum guide gives the students a hint by telling them that natural chalk is made of a chemical compound called calcium carbonate.

Carbonate contains carbon. The students know that this is an important fact about chalk. Carbon is an essential element in all organisms. Carbon is the basic element in the molecular structure of all organisms. Plants need carbon to grow and reproduce. Animals obtain carbon by eating plants or other animals. Carbon compounds are a source of energy for living things.

Chalk is not a living thing. The students search for more facts to link chalk to living things. The museum guide stated that all the answers can be found in the museum. In the shell exhibit,  the students were told that shells of marine animals are made of calcium carbonate. This fact connects the chalk to living things. The students turn their attention to the carbon in the air. The carbon cycle is a biogeochemical cycle.

The carbon cycle is a biogeochemical cycle. Carbon atoms move between living and nonliving factors. Living factors in the carbon cycle are all living things on earth. Nonliving factors are the air, bodies of water, rocks, and decomposed organic matter in soil.

Dinosaurs and other animals release carbon dioxide into the air. The carbon dioxide is a product of respiration that occurs in cells of living things. The carbon dioxide can circulate and reach the air above an ocean.

The carbon dioxide can be absorbed by ocean water at certain temperatures. The carbon dioxide dissolves in the water and forms carbonate. Marine organisms use the carbonate in the water to form shells. This connects carbon dioxide to shells.

The students must find out facts to connect the shells to chalk. In the museum’s hall of rocks and gems, they learn that chalk is a form of limestone. Limestone is made of calcium carbonate. It is formed mainly from the shells and bones of dead marine animals. As the animals die, they fall to the floor of the ocean. As time goes on, layers upon layers are packed on top of each other. Over millions of years, limestone is formed.

This completes the path of carbon from dinosaur to chalk. Carbon dioxide is exhaled. The carbon dioxide is absorbed by the ocean. The carbon dioxide forms carbonate in ocean water. Marine animals use carbonate to make shells. The shells and bones of dead marine animals settle at the bottom of the ocean. After millions of years, the layers form limestone, or chalk.

Carbon in limestone can remain stored for millions of years. It can enter the carbon cycle again when magma pushes through limestone during a volcanic eruption. The carbon dioxide that is given off during the eruption comes from the limestone. The carbon dioxide enters the air and can be used in the cycle again.

Under certain conditions, sediments on the ocean floor can become fossil fuels. Examples of fossil fuels are oil, natural gas, and coal. After being stored for millions of years, the fuels are extracted. Carbon dioxide is released into the air when the fuels are burned for energy. This carbon dioxide can be used in the cycle again. Carbon also cycles in a much quicker path. Carbon dioxide in the air is taken in by plants. The plants use carbon dioxide for photosynthesis. Through this process, the carbon in carbon dioxide is used to make the glucose molecule.

Animals obtain this carbon by eating plants and other animals. The glucose is broken down during respiration in plant and animal cells. Carbon dioxide is a product of respiration. Carbon dioxide is released into the air by plants and animals. The carbon dioxide can be used in the cycle again.

Carbon is stored in dead plants and animals. It is also stored in animal wastes. The stored carbon can re-enter the carbon cycle when dead matter and wastes decompose. The carbon dioxide that is a product of decomposition enters the air. It can be used in cycle again.

The environment can be harmed when the carbon cycle is disturbed. Carbon dioxide levels in the air are increasing in several ways. Carbon dioxide is released into the air when automobiles and factories burn fossil fuels.

Forest fires release carbon dioxide into the air.  Large areas of forests, grasslands, and wetlands are being removed by humans.  There are fewer plants to remove carbon dioxide by photosynthesis.  Carbon dioxide is a greenhouse gas.  Higher greenhouse gas levels in the air lead to higher temperatures.  This is called global warming.  

Carbon is the building block of life. Carbon atoms are not destroyed. They are recycled between the living and nonliving factors on earth. They move from the air to living things. They can move back to the air and re-enter the carbon cycle. They can also be stored for millions of years. And, as the students found out, carbon from a dinosaur’s breath can become chalk.

Have you ever wondered how life began on Earth? Or what these early forms of life look like? Scientists have various theories as to how life began on Earth. But, the recent discoveries of the five basic components of DNA in meteorites, have the scientific world buzzing with the idea that the ingredients of life could have been delivered from outer space to the infant Earth as meteorites bombarded the planet.

We know from geological evidences that volcanic activity rocked the Earth during its early years. Comets and asteroids pounded its surface.

Evidence supports that many basic building blocks of life form naturally in space. Meteorites and comets contain several amino acids that living organisms need to make protein. Therefore, this leads to the idea that as the asteroids smashed onto the surface of the Earth, they brought with them the necessary ingredients for life to begin on Earth.

There are many alternative hypotheses as to how life first started. According to some scientists, life started in a primordial soup. This theory states that in the early Earth a mixture of organic molecules was produced from simple inorganic molecules. Some suggest that life began in the deep ocean vents. Still others think that it began in hot springs on the surface of the Earth where complex compounds were formed from simple ones.

According to some scientists, DNA is too complex and probably life started as a form of RNA. Whether the essentials of life came from outer space or were formed in a primordial soup is still not known.

Scientists have found evidence that meteorites that fell to the Earth contain the five bases that are important in the formation of DNA and RNA. DNA structure is made up of two strands that are linked together. These strands are twisted around each other into a double helix. The building blocks of DNA are nucleotides. The nucleotides are made up of a phosphate group, sugar and one of four nitrogenous bases. The bases adenine, guanine, cytosine, thymine (found only in DNA), and uracil (found only in RNA) along with sugars and phosphate make up the genetic code.

DNA and RNA contains all the instructions necessary for a living organism to develop and function on Earth. Of the four nitrogenous bases, cytosine and thiamine are pyrimidine bases and adenine and guanine are purine bases. The sequence of these bases’ codes for all the instruction to build and maintain an organism.

Scientists have found adenine, guanine, uracil and other organic compounds. But until now, cytosine and thymine were not found in meteorite samples. These pyrimidine bases are very delicate and fragile. To analyze the molecular content of chemicals in the meteorite, scientists place the meteorite grains in a hot bath. The molecules are then extracted using formic acid. This is a highly reactive process. This process could have destroyed very fragile molecules like cytosine and thymine.

Geochemists have recently used a new technique to gently extract and separate the different compounds found in the samples. They used cooled water rather than heated water. Also, more sensitive analysis methods were used. These methods are capable of tracing very small samples present in solutions.

Geochemists and astrochemists have found ribose and several other sugars in samples of meteorites. Tests have shown that the sugars in these meteorites most likely originated in space and were not picked up from soil on Earth. A simulation of space environment in laboratory has shown that ribose could have formed in ice grains found in interstellar space.

Scientists are working diligently to prove that these compounds are extraterrestrial and not due to contamination from soil. Using the improved methods of analysis, researchers have found other isomers of the nucleobases in meteorites. Isomers have the same chemical formula but the organization of the components are different. The isomers have been found in the meteorites but not in the soil. According to the researchers, if there had been contamination from the soil then the isomers would also have been detected in soil samples. Their absence proves that these compounds originated in the meteorite.

What would you do to prove that something came from one specific place? You would probably go to the source and find examples of that item. Right? That is exactly what is being done today.

Scientists are already using the new extraction methods on samples from the surface of the asteroid Ryugu. Asteroid Ryugu was visited by Japanese spacecraft in 2020. The samples collected from the asteroid are presently being analyzed. Since these are pristine samples directly from the asteroid, they would be free of contamination from the soil. This would be a step forward to show that asteroids may have been the vehicle that delivered the major ingredients of life to Earth. Also, one of NASA’s missions to asteroid Bennu will soon bring back more samples. This would further help our understanding of the role that asteroids played in the puzzle as to how life began on Earth.

So, next time you gaze at the night sky and wish on a shooting star, just think of the possibility, that life on Earth could have had its beginning somewhere out there in space. Isn’t that exciting!!

Jeremy was with his ninth grade class on a field trip to the Museum of Natural Science. Currently they are learning about evolution in Biology. The fossil room mesmerized him. He was curious to know more as they looked at impression of strange looking organisms and small pieces of bones and teeth. The guide was explaining to them how these very important finds help scientists to piece together a picture of the organisms that lived on Earth millions of years ago and how they changed over time. The story of evolution is like a book, he said, with a lot of missing words, paragraphs, and pages. It is an important field of study. 

Every organism that we see today has evolved over time through natural selection shaped by adaptation to changing environment. Jeremy was intrigued. The next day in class he learned that one of the ideas as to how evolution occurred is known as gradualism. What is gradualism? Gradualism, as the name suggests is defined as gradual, consistent changes over a long period of time. In the process of evolution, accumulation of changes over time result in new species. The theory of gradualism is not new at all. Charles Darwin thought that evolution was a steady, slow, and continuous process. The idea that there are transitional forms between related species have been around for a long time. This theory proposes that evolution occurs at a constant rate. The transition between different stages is slow rather than sudden spurts after a period of no change.

Scientists who belong to this school of thought use fossil evidence as the proof. Transitional intermediate fossils from related species show evidence that there was structural adaptation over the years as organisms adapted to new environment. Over millions of years, this led to new species. According to the theory of gradualism, we see the sudden appearance of certain species because fossil records are incomplete.

Fossil record gives us a glimpse of evolution over billions of years. But why are fossil records incomplete? Why are fossil so rare? What happened to the remains of all those animals from millions of years ago? The truth is that most organisms never become fossils. The likelihood of organisms being fossilized is very rare. The formation of a fossil is very complex and requires all conditions to be at its optimum to prevent the fossil from decay and destruction. And then there is the question of finding them. Unfortunately, most of the fossils of past living things will not be found. They could be buried deep or may be in locations that we are not digging yet.

The Cambrian period is an important period in the evolution of life on Earth. It seems to be the time when major groups of animals first appeared. Many major phyla that make up the modern animal phyla seemed to have appeared at this time. Scientists have been puzzled by this “Cambrian Explosion”. During this time the diversity of life seemed to have increased at a tremendous pace.

With new technology and an understanding of developmental biology, some of the previous ideas have been modified as scientists unearth new fossils. Improved understanding about how changes occurred in the body due to environmental factors have led to a different explanation of the Cambrian explosion. New studies seem to show that organisms increasingly became more and more complex rather than diverse. During the Cambrian era some of the first fossils of species with an exoskeleton were found.

The new school of thought is that there seems to be the presence of diverse fossils during this period simply because of the evolution of hard body parts. Scientists think that during this time, species adapted to the environment, and more developed exoskeletons to survive attacks from predators. These harder structures preserve better than soft tissue that was characteristic of animals of the pre-Cambrian era. Hence there is more fossil evidence of the Cambrian era than of any previous geologic time.

Recent fossilized remains found in Australia seems to represent organisms belonging to pre-Cambrian chordates. These provide a link between pre-Cambrian chordates and the phylum that humans belong to. Some fossils have features that indicates that they evolved before some of the species that existed after the Cambium period. As our understanding deepens, it seems that modern existing phyla have gradually evolved over a larger geological time period than we had previously thought.

During field work in Namibia, scientists using an X–ray imaging technique found well preserved soft tissue of animals. These fossils were found in mineral called pyrite. Comparative studies have shown that these were fossils of an early ancestor that appeared during the Cambrian explosion. These fossils help scientists to better understand the history of life and provides support for gradualism in the evolutionary process. 

Jeremy was surprised that the theory of gradualism also extended to flowering plants. The origin of the flowering plants had puzzled Darwin and other scientists. Flowering plants made a sudden appearance in fossil record recently in geological time. But genome data shows that they originated much earlier. A new study based on fossil record only shows that flowering plants did exist more than 100 million years ago. The older fossils have not been found simply because flowering plants were rare and the probability of fossilization as we know is very low. Scientists think that the flowering plants were overshadowed by ferns and gymnosperms which were the dominant species in the early ecosystem. Gradually over time they became the most abundant and diverse group on earth.

Jeremy was very intrigued by the fossils that he saw that day. He realized that more evidence and research are needed to find out the true process of the evolutionary mechanism. He wondered if he could study to become a paleontologist and one day help to piece together the big jigsaw puzzle of the fossil record. The thought put a big smile on his face as he walked home.

Amira noticed a bee covered with pollen in her garden. She knows that the bee is helping the flowers, but she wonders if other living things have close relationships.

A honeybee collects nectar from a flower. Pollen grains attach to the bee’s back. The honeybee moves from flower to flower. Pollen grains fall off the honeybee onto other flowers. This relationship helps to keep the ecosystem stable. There are many relationships between species in a community. The communities can be affected in positive and negative ways.

Both species benefit in the flower and honeybee example. The honeybee collects nectar to feed the bee colony. The pollen can fertilize the eggs in the flowers. This allows the flowers to continue reproducing. This long-term relationship is called mutualism. Both species benefit in mutualism. The ecosystem also benefits. It continues in a steady state. This helps the community remain stable.

A bird builds a nest high in a tree. The nest is hidden by branches and leaves. The location protects the eggs and young. The bird uses twigs from the tree to build the nest. Seeds from the tree can feed the young. The birds benefit greatly from this relationship. The small nest does no harm to the tree. The tree does not benefit. This relationship is called commensalism. One species benefits while the other is not affected.

Species interact when they share resources. The resources are needed for a species to grow and reproduce. The species are in competition because the resources they need are limited. Competition can occur between different species. It may also occur between organisms of the same species. This can lead to the decline of one or both species. The decline can lead to reduced growth. The decline can also decrease reproductive rates.

Grass growing under a tree is thin.  This is due to competition between the grass and the tree.  Some trees planted too closely may not reach their full height.  This could lead to the extinction of a species. Plants compete for nutrients, water, sunlight, and space. Competition can lead to the extinction of a species. This loss of diversity can lead to a less stable ecosystem.

One species lives in or on a host species in parasitism. The host is harmed in this relationship. The parasite benefits from keeping the host alive. The parasite will keep the host alive for days or years. Parasites are common among insects. Many insects lay their eggs within the body of another species’ larva. When the eggs hatch, the parasitic young kill and eat the larva.

Bacteria, fungi, and worms are all parasites that invade humans. Parasites cause infectious diseases in humans. Many of the parasites in humans also invade other small mammals and birds. Wheat, fruit, and vegetable plants can be invaded by different species of fungi. Parasites can limit populations. Parasites do not cause extinction. This helps to keep an ecosystem stable. In predation, one species benefits. The species that benefits is called a predator. The other species is killed. It is called the prey.

The predator hunts, captures, and kills its prey. Predators are adapted for hunting and killing. They have strong bodies and swift movements. They also have highly developed senses. Some predators hunt alone. They are usually larger than their prey. A snake will kill and eat a small rodent on its own. Others hunt in groups. This helps when the prey is much larger than the predator. Lions hunt for large buffalo in groups. A pod of orca hunt for large sperm whale. Predation helps to control populations. This helps the community remain stable.

Amira has learned that almost every species of living thing has a close relationship with another living thing. A stable ecosystem remains in an average state where everything is balanced.  A stable ecosystem returns to its average state after being disturbed.  Diversity helps to buffer losses in an ecosystem.  Relationships between species affect stability.  Examples of these relationships include predation, parasitism, commensalism, mutualism, and competition.

Each day on the way to lunch, Ben stops by the nurse’s office to take a pill. When asked why he needs the pill, Ben said that he is lactose intolerant. He gets an upset stomach when he eats or drinks dairy products. Lactose is a sugar molecule naturally found in milk. He said that the pill keeps him from getting sick when he eats ice cream during lunch. Most of his friends said that they know people who are also lactose intolerant. They do not understand exactly what that means. But they are happy that there is a pill that lets Ben eat his ice cream every day.

What Ben’s classmates may not know is the pill that he takes to digest lactose has a substance called lactase. The -ase ending in a name means that it is an enzyme. Enzymes belong to the group of molecules called catalysts. Catalysts are substances that speed up chemical reactions without being used up. Enzymes are catalysts that occur in all living things.

There are thousands of different enzymes in organisms. Some are digestive enzymes, like the lactase in Ben’s pill. They break down foods and nutrient molecules. Other enzymes control cellular processes that occur in organisms. Some of the processes build molecules. Other processes break molecules apart. DNA replication is a process that involve a series of reactions. It relies on many enzymes to control the reactions from start to finish.

The reactants in a chemical reaction must absorb a certain amount of energy for the reaction to begin. This is called activation energy. Enzymes and other catalysts lower the amount of energy needed to start a chemical reaction. This increases the rate of the chemical reaction. The energy can be compared to the amount of energy needed to push a rock over a hill. There is a certain amount of energy needed to push the rock to the top of the hill. Then, the rock can roll down the other side by itself. Once the reactants absorb enough energy for the reaction to start, it can continue by itself.

The reactant, or substrate, binds briefly to a special area on the enzyme molecule called the active site. The active site will change slightly to fit the substrate. This action is like the change of your grip when you shake another person’s hand. The slight change places the substrates into the position needed for the reaction to take place.

The bonds of the substrates are stretched in the active site. This weakens the bonds of the substrates. It lowers the amount of energy needed to change the substrates to products. The products break away from the enzyme. The active site is now free for another substrate to briefly bind to it and repeat the process.

Enzymes are large protein molecules folded into very specific 3D shapes. The function of the enzyme depends on its structure. Only certain reactants can bind to the specific shape of the enzyme. The enzyme is specific for a reactant just as a lock is specific to a key. For example, the enzyme that breaks down lactose will not break down similar sucrose or maltose molecules.

The lactase enzyme is specific for the reaction that breaks down lactose into simple sugars that can be used by cells. Lactase is produced in the small intestines of humans and other mammals. Lactase molecules are shaped to fit only lactose molecules. When mammals drink milk, lactose will be broken down by the lactase enzyme in the small intestines.

People who are lactose intolerant do not produce enough lactase to break down the lactose that they eat and drink. The lactose molecules cause pain as they make their way through the intestines. The lactase enzyme in Ben’s pill breaks down lactose just like naturally produced lactase. This takes away some of the pain that lactose intolerance can cause. It also allows Ben’s cells to take in the important simple sugars that are produced when lactose is broken down.

There are many inherited disorders that are caused by not having enough of an enzyme. Some of the disorders, like lactose intolerance, are caused by a lack of enzymes that break down foods. This robs the organism of important energy molecules. It also robs the organism of raw materials to build more cells. There are other inherited disorders caused by a lack of enzymes that break down cellular wastes. Over time, harmful amounts of the wastes build up in cells, tissues, and organs.

Enzymes are found in all cells of organisms. They are important molecules with very specific structures that provide very specific functions. They allow chemical reactions to occur quickly under the normal conditions in an organism. Enzymes play an important role in every cellular process.

Have you ever heard of a chemical called cyanide? Plants like almonds and lima beans contain this deadly poison. Apple seeds and peach pits also have cyanide. The amount of cyanide in these plants is very small and cannot cause harm unless eaten in large amounts. You are exposed to much more cyanide in cigarette smoke or to chemicals released from burning plastic. Cyanide is mainly used in making paper, plastics, and pesticides. Workers in industries that use cyanide must take safety measures so that they do not breathe in cyanide.

Once inside living things, cyanide stops cells from using oxygen. In humans, cyanide affects the heart and the brain most because these two organs use more oxygen compared to other body organs. During World War II, the Nazis used cyanide gas to murder people.

Animals like millipedes produce cyanide to defend themselves. They can spray a liquid containing cyanide from glands on predators. It is a form of chemical warfare that causes irritation to anything that wants to eat a millipede. To understand how cyanide stops cells from using oxygen, you need to know what cells actually do with oxygen. You probably know that people breathe in oxygen and breathe out carbon dioxide, but what happens in between?

Oxygen is present in our atmosphere and comes from photosynthesis. Plants can make glucose (food) by combining carbon dioxide and water using energy from the sun.

Living things that cannot perform photosynthesis must eat other organisms for energy. Digestive systems break down food into smaller parts like glucose that can enter cells. Cellular respiration is the process that breaks down glucose to get energy for the cell.

Most cellular respiration needs oxygen. There are a series of proteins in a cell structure called the electron transport chain. The proteins in the electron transport chain move electrons from one place to another. They also transfer protons (hydrogen ions) across a membrane. The hydrogen ions (H+) will combine with oxygen, forming water as a waste product.

This process happens in the mitochondria of a cell, and when oxygen accepts these hydrogen ions, energy from this reaction makes adenosine triphosphate (ATP) which the cell uses for energy. This is why a mitochondrion is known as the “powerhouse” of a cell.

Oxygen is needed to form adenosine triphosphate (ATP). ATP is needed to do cellular processes like active transport and cell division. Without oxygen, most cells cannot get enough energy to conduct necessary tasks, and they will begin to die.

Cyanide will easily bind to the part of blood that carries oxygen and taken to all tissues in the body. It can then move by diffusion into cells. Once inside a cell, cyanide will move into a mitochondrion and bind to cytochrome oxidase, a protein molecule that is important in the electron transport chain. When cyanide binds to cytochrome oxidase, the entire process stops, and the cell will have no energy.

The effect of cyanide poisoning depends on how much cyanide enters the body. Low level exposure can lead to headaches, dizziness, and confusion. Cyanide is one of the deadliest poisons known to man. Fast treatment is needed for high levels of exposure, and treatment can be given with medicine that binds to cyanide to remove it from the body. High levels of exposure can have long-lasting effects, especially in the nervous system. Part of the brain called the basal ganglia are very sensitive to cyanide. This part of the brain controls memory and motor movement. Damage to this system leads to memory issues and shaking of the hands found in people with Parkinson’s disease.

It is hard to believe that something like a tiny apple seed can contain such a dangerous chemical. Of course, you would have to eat quite a bit to have a poisonous effect. But now you know why you never eat the core of an apple!

It is natural for populations to change from one generation to the next. Maybe you have seen a small patch of wildflowers with an even mix of red and white varieties. Over time, you notice fewer and fewer white flowers. What is causing the changes in this population? The simple answer is that the changes are due to chance. There are several evolutionary mechanisms, or processes, that can cause the random changes.

Chance can cause big changes in small populations. By chance, a population of ten rabbits loses five members that had never reproduced. The five rabbits may have died before reaching the reproductive age. Or the rabbits may have lived an entire lifetime without reproducing. The rabbit population would lose 5/10 or 50% of its gene pool. The gene pool is made up of all the alleles in a population. Alleles are different versions of the same gene.

Look at the diagram of the rabbit population. See how random chance changed the gene pool from the first generation to the second? This change due to chance is known as genetic drift.

Look at the rabbit diagram again. Observe what happens to the gene pool between the second and third generations. The recessive gene was erased due to chance. The number of gene versions decreased from two to one. This means the genetic variation, or diversity, has decreased. Genetic drift can result in a loss of diversity.

Genetic drift can apply to a large population that loses a lot of members. This can happen after a natural disaster. A fire can wipe out a large portion of a forest. Members survive by chance. The gene pool of the survivors may be very different from the original. There may be a higher percentage of some alleles. There may be a lower percentage of others. Some may be completely erased.

Imagine a small population of white wildflowers. How can we explain the sudden appearance of red wildflowers? The red allele has moved into this population. There might be a nearby mixed population of the same wildflower. Insects carry pollen from flower to flower. The wind can randomly blow pollen between populations. Pollen contains genes.

Gene flow is the process that moves genes from one population to another. Genes can flow in both directions. Genes can be removed from a population. Some can be added to a population. Over time, the original white population will be a mixture of red and white flowers. Gene flow makes populations more similar.

What if a white variety of the flower did not exist? Suddenly a white flower appears in a population of all red. A change in the DNA of the flower color gene may have occurred. Mutation is a process that causes a permanent change in the DNA structure. The change must be able to be passed on to offspring.

Mutation introduces new versions of genes into the gene pool. Diversity is increased. A mutation is random. It does not appear because an organism needs it.

Sexual reproduction generates new combinations of genes in offspring. These combinations are not found in the parents. This process is known as genetic recombination.

Students were gathering excitedly in Professor Pickens science class. He was just back from working with a group of evolutionary biologists who are studying the cichlid populations found in Lake Apoyo, a remote volcanic lake in Nicaragua. Students wanted to know what interesting things he learned and of course they anticipated beautiful images that he always brought back.

“Today we will talk about speciation,” said Professor Pickens, “especially sympatric speciation.” And so began their journey into the amazing realm of forming new species through the evolutionary process. Speciation happens when groups within a species,  for various reasons, are reproductively isolated from each other.

There are different ways that speciation can occur. Sympatric speciation is unique and can be controversial. In sympatric speciation, the subpopulations occupy the same area, but are genetically different enough so that they can no longer breed together, and are therefore considered to be two different species.

Sympatric speciation could occur due to behavioral isolation, which is isolation that could be based on unique mating calls or courtship rituals. It could be temporal isolation, isolation caused due to difference in mating season and sexual maturity.

Sympatric speciation occurs when there are no physical barriers separating members of the different species from each other. So, what causes two distinct species to develop? To answer this, we go back to the cichlid populations of Lake Apoyo, the crater lake Professor Pickens visited.

Two species of Midas cichlid fish are found in Lake Apoyo. The two species have slight differences in body shape and jaw structure. They cannot interbreed. Research shows that the two species live at different depths within the lake. One lives in open water while the other lives in deeper water. Competition for food could have led some to look for food in the deeper waters. As they continued to stay in the deeper waters, feeding and living in different depths than the original species, sympatric speciation might occur. Over time, this would lead to a different species incapable of interbreeding with each other.

Cichlids in the African Great Lakes also shows sympatric speciation. Females choose males that have same coloration that she does, which helps maintain the sympatric speciation in the lakes. Male cichlid quivers as a display for females. This produces a certain number of pulses and pulse periods. The female chooses mates by selecting numbers and rates of pulses found within her species to increase the chances of survival of the offspring.

Recent sympatric speciation may be occurring in the apple maggot fly. The flies lay eggs on fruits of hawthorn trees. But after the introduction of apples in the 19th century, some lay their eggs on apples instead. The flies usually look for mates and lay eggs on the same fruit that they grew up on. So, over time although they are in the same geographic area, speciation will probably occur between the two groups of the same species, based on their preference of the fruits they lay their eggs on.

Professor Pickens continued to show more images and examples of other types of behavioral isolation that led to speciation. The examples of the Eastern and Western meadowlarks showed two birds that looked very similar to each other, but the Western meadowlarks and Eastern meadowlarks are two distinct species that arose from the same ancestral species. They have different mating calls. The Western meadowlark does not respond to the mating calls of the Eastern meadowlark, and vice versa. Since the two do not mate they are considered to be two different species.

Students were surprised to learn of a rare example of sympatric speciation in orcas in the Pacific Northwest. The “resident”, “transient” and “offshore” orcas hunt for different prey. The “resident” orcas feed exclusively on salmon and are found in nearby coastal waters. The “transient” orcas feed only on marine mammals and move north to south along the coast. The other group known as the “offshore orcas” are found well beyond the coast and sharks are an important part of their diet. The social structure of each population is different as well as their form of communication. They do not interbreed although they inhabit the same areas.

Did you know that there are many species of fireflies and each have their unique flashing lights? What is so special about that is the fact that different species of fireflies have very distinct patterns of flashing lights. Members of the same species find mates using their unique flashing patterns. This prevents breeding between different species, since the female will not mate unless she recognizes the light pattern.

Have you seen a blue-footed booby dance? Well, the blue-footed booby shares its habitat with other species in the same genus, but it never mates with the other species. Its behavioral isolation is promoted by its elaborate courtship ritual. The female blue-footed booby selects a mate after watching the entire ritual dance.

Sympatric speciation is common in plants due to polyploidy. Polyploidy results due to errors in meiosis that create extra chromosomes. New plants can grow in the same environment as the parent but are reproductively isolated due to the difference in number of chromosomes.

In the remote Lord Howe Island near Australia, there are two distinct but closely related palm trees. They are found in two areas of the island. The soil pH is different in these two areas. Palms send pollen through the air, so these two varieties could interbreed, but since speciation has already occurred, they do not produce viable hybrids. In this case, sympatric speciation could have occurred due to competition for soil to grow on.

Temporal isolation happens when two or more species reproduce at different times. There are three species of orchid that live in the same rain forest. Each species has flowers that last only one day. The flowers must be pollinated on the same day to produce seeds. But each species flowers on different days and therefore cross pollination does not occur.

Some flowers evolve to attract specific pollinators. The structure for access to the nectar varies. An example would be the two different species of monkey flowers. The pink flowers are more open in structure. They are pollinated by bees. The red flowers are narrower and are pollinated by hummingbirds. The hummingbirds can reach nectar deep within the narrow tubes while the bees prefer the wider floral tube to access the nectar. This prevents cross pollination between the two different species of monkey flower, even though they occupy the same general area.

Temporal isolation also occurs when two related frog species show reproductive isolation since one species breeds earlier in the year than the other.

“And so, there you have it,” said Professor Pickens as he ended his lesson with a few examples of sympatric speciation.  I hope the examples help you understand how speciation can occur even though there are no physical barriers separating the two species. We must therefore wonder, how much of our diversity is due to sympatric speciation, and how often is it happening in nature.”