QUESTION 1
Biological evolution is the change in the frequency of alleles in a population over time (KF, Lecture). The assumptions of the Hardy-Weinberg Equilibrium model which are as follows: “(1) No mutation takes place, (2) No genes are transferred to or from other sources (no immigration or emigration takes place), (3) Mating is random (individuals do not choose mates based on their phenotype or genotype), (4) The population size is very large, and (5) No selection occurs” help keep biological evolution from occurring (Raven, p. 399). However, violations of this model lead to biological evolution through the following: mutation, gene flow, non-random mating, natural selection, and genetic drift (KF, Lecture).
The process of mutation violates the Hardy-Weinberg assumption that (1) No mutation takes place (Raven, p. 399). Mutation occurs when one allele changes into another allele (Raven, p. 401). This shift in allele balance causes biological evolution to occur (Raven, p. 401). If an allele that controls the color of a flower changes then the petals of that flower may change from red to white for example. Despite the fact that actual chance of mutation occurring is very rare, it is the “ultimate source” of altering genes therefore causing biological evolution to occur (Raven, p. 401).
Another violation of the Hardy-Weinberg Equilibrium model is gene flow. Gene flow violates the assumption that no genes are transferred to or from other source (no immigration or emigration takes place) (Raven, p. 399). As its name would suggest, gene flow occurs when the alleles from one population move to another population (Raven, 401). This process of transferring alleles from one population to the next causes biological evolution to occur; because, it causes populations to be exposed to a new set of alleles, often a rare set of alleles will be exposed through gene flow as well (Raven, p. 401).
The next violation of the Hardy-Weinberg Equilibrium model is nonrandom mating. This violation defiles the assumption that mating is random (individuals do not choose mates based on their phenotype or genotype) (Raven, p. 399). Non-random mating is referred to as assortative mating (Raven, p. 402). Assortative mating occurs when two individuals that are phenotypically similar mate (Raven, p. 402). The genotypes of the offspring produced through assortative mating are extremely different than what would be predicted through the Hardy-Weinberg Principle (Raven, p. 402). This fact leads to biological evolution because assortative mating increases the quantity of homozygous organisms in a population rather than the quantity that would typically be expected (Raven, p. 402).
Yet another violation that causes biological evolution is genetic drift. Genetic drift violates the assumption that the population size is large (Raven, p. 399). Small populations run the chance of certain alleles changing at random (Raven, p. 402). “Such changes in allele frequencies occur randomly, as if the frequencies were drifting from their values…known as genetic drift” (Raven, p. 402). The example within the text refers to the fact that in a small population the alleles that a few individuals carry that form the next generation may not be expressed fairly in their offspring (Raven, p. 402). Even though, larger population experience genetic drift, smaller population experience it more severely and often times in a negative way (Raven, p. 402). This is why genetic drift is a violation that causes biological evolution.
Natural selection is the final violation that causes biological evolution. Natural selection violates the assumption that no selection occurs (Raven, p. 399). Natural selection is the process by which organisms attempt to increase their fitness (Raven, p. 405). Fitness is “a combination of survival, mating success, and number of offspring per mating” (Raven, p. 405). An example would be if a particular tasty flower had the ability to produce two different flower colors. The green flowers are more easily disguised in the forest as compared to its red flower counter-part. The red flowers are then more likely to get pollenated than the green ones. Therefore, phenotypically the red flowers have a greater fitness than that of the green flowers. Continuing, the red flowers will be more prevalent in the next generation. This is how natural selection is an example of biological evolution because it changes the frequency of alleles in a particular population.
All of these violations of the Hardy-Weinberg principle can act independently or together in order to create biological evolution.
QUESTION 2
The first organism pictured is an angiosperm because of the fact that it has a flower. Because this image is an angiosperm, its hierarchical system begins with Charophytes (KF, Lecture). Charophytes are more closely related to protists and they are green algae (KF, Lecture). Next, branching from the Charophytes, comes the Bryophytes (KF, Lecture). The Bryophytes developed stomata, some specialization of root-shoot system, and distinguishing sporophyte and gametophyte (KF, Lecture). After the Bryophytes comes the Tracheophytes, more commonly known as ferns and lycophyta, developed vascular tissue and Euphylls (“Early leaves”) (KF, Lecutre). Finally, branching from the Tracheophytes comes the angiosperms because they developed fruits and flowers.
They main reason to identify the plant as an angiosperm is the fact that it has a flower. Angiosperms are very diverse and their history is complex and often misunderstood (Raven, p. 606). Fruits and flowers allow for the angiosperms diversification (KF, Lecture). The flower facilitates pollination for the angiosperm and fruits facilitate seeds and allow for the dispersal of seeds (KF, Lecture).
The next organism is a snail. This is clearly seen because of key characteristics of mollusks.
The phylogenic tree for mollusks begins with protists. Therefore a mollusk is a protostome because a protostomes have bilateral symmetry (KF, Lecture). The next branch of the tree is the spiralia. Organisms classified as Spiralia exhibit spiral cleavage as well as gradual growth (Raven, p. 645). The classification of Spiralia divides into two clades of spiralians: platyzoans and lophotrochozoans (KF, Lecture). The mollusks fit in the category of lophotrochozoans because they have trochophore which are free-living larvae (KF, Lecture). They also have a lophophore which is a feeding structure that is shaped like a horse-shoe shaped structure of ciliated tentacles around the mouth (KF, Lecture). After being placed in the category Lophotrochozoans, this organism is placed into the group Mollusca, more specifically Gastropoda (snails and slugs). Snails are placed into the Mollusca group because snails have a mantle which is a thick epithermal sheet that covers the dorsal side of the mollusk. Mollusks have calcium carbonate shell, muscular foot, bilateral symmetry and a radula (KF, Lecture).
Gastropoda have a few distinct charecteristics that make them fit into this category. One of their characteristics is torsion (Raven, p. 668). Torsion requires the mantle cavity and the anus move to the front of the body (Raven, p. 668). Gastropoda also have exposed gills; however, terrestrial gastropoda are ones can close the opening of their lungs (KF, Lecture). Because a snail exhibits these attributes, it is placed in the Gastropoda category.
The final picture is a dinosaur. This picture is of a dinosaur; however, this dinosaur exhibits qualities that are closely related to birds. This dinosaur has small arms; and no apparent feathers. Because of that fact, I would place this dinosaur somewhere in between a Tyrannosaurus and a Sinosauropteryx (Raven, p. 465). I placed the pictured dinosaur in between these two classes of dinosaurs because this pictured organisms has already lost fingers 4 and 5, but it has not developed feathers or long arms (Raven, p. 465).
After the Sinosauropteryx comes the Velociraptor that has not only developed downy feathers, but also long arms, highly mobile wrists, feathers with vanes, shafts, and barbs (Raven, p. 465). After the Velociraptor comes the Caudipteryx which has developed long, aerodynamic feathers (Raven, p. 465). Branching from the Caudipteryx comes the Archaeopteryx which has developed arms longer than its own legs (Raven, p. 465). Finally, after the Archaeopteryx, with the loss of teeth and the reduction of a tail, comes the modern bird (Raven, p. 465).
Clearly from all three of these examples the process of evolution is not a simple one-step process, but actually more like a step-by-step process. It is hard to believe that burly dinosaurs evolved into light birds capable of flight (Raven, p. 465). However, the fossil record proves that indeed birds did evolve from dinosaurs. These hierarchical structures not only help scientist categorize organisms, but also help scientists receive a better grasp on the understanding of evolution.
QUESTION 3
In order to compensate for being multicellular, organisms have to abide by Fick’s Law. Fick’s Law states that, in order to thrive, multicellular organisms need to decrease the distance between the oxygen and their cells, increase the surface area, and increase the concentration gradient (KF, Lecture). Organisms have to abide by Fick’s Law in order to make their rate of cell diffusion greater than their rate of cellular respiration (KF, lecture). Multicellular organisms have developed systems to compensate for this inconvenience.
The first organism is a grasshopper which has developed an intricate respiratory system in order to abide by Fick’s Law. In order to increase surface area, the grasshopper’s respiratory system has developed tracheae which are, “small, branched, cuticle-lined ducts” (Raven, p. 681). Because the ducts are branched and have lining in them, the surface area has greatly increased. The increase in surface area helps for diffusion to occur faster and more efficiently. The grasshopper decreases the distance that the molecule must diffuse by having tracheoles. Tracheoles branch from the trachea so close that they are in direct contact with the grasshopper’s cells. In order to increase the concentration gradient by allowing a continual flow of oxygen from the outside environment into the artificial internal environment that the grasshopper has created. Grasshoppers have openings in their sides called spiracles that allow for the continual flow of oxygen throughout their respiratory system (Raven, p. 681). All of these points help the grasshopper overcome the issues caused by being multicellular through abiding by Fick’s Law.
In a fish, its respiratory system has shown how it has developed to abide by Fick’s Law. First, fish have gills. These gills basically extended tissues (Raven, p. 1004). These tissue extensions create much more diffusion surface area which allows them to extract so much more oxygen from the water, than what they could without them (Raven, p. 1004). The gills themselves even have extensions called gill filaments which create even more surface area (Raven, p. 1005). In order to decrease the distance from the cells to their oxygen and nutrients, gills have developed to be approximately one epithelial cell thick which allows diffusion to be less difficult (Raven, p. 1004). The final issue fish needed to solve was how to increase the concentration gradient. Fish have developed a system to greatly increase the concentration gradient of oxygen in their system by using countercurrent flow (Raven, p. 1005). While the oxygen rich water flows solely in one direction, the fish’s blood flows in the opposite direction (Raven, p. 1005). This countercurrent flow system allows the blood that is leaving the gills to have about just as much oxygen as the water does (Raven, p. 1005). The respiratory system of fish is very efficient because it has abided by all of the principles of Fick’s Law.
The next organism that has abided by Fick’s Law is the jellyfish. The digestive system of the jellyfish increases the concentration gradient by only having one opening that is both the mouth and he anus (Raven, p. 982). The constant flow of food and waste in and out of the gastrovascular cavity increases the concentration gradient for Fick’s Law (Raven, p. 982). As previously stated, jellyfish have a gastrovascular cavity which actually means that they participate in extracellular digestion throughout this cavity (Raven, p. 982). All of the cells of the jellyfish participate in all of the digestive stages because jellyfish are only one to two cell layers thick; therefore, cells are either directly exposed to the gastrovascular cavity or the environment (Raven, p. 982). This fact is the evidence that jellyfish have evolved to decrease their diffusion distance. In order to increase surface area, jellyfish have tentacles which help catch its food (Raven, p. 982). These tentacles contain special cells called nematocysts, which, once tripped, a harpoon stinger is projected (KF, Lecture). The tentacles and their ability to sting have increased the surface area of the jellyfish allowing it to capture its food more efficiently. Therefore the jellyfish is another example of how this organism has evolved to abide by Fick’s Law.
Within this strawberry plant, the vascular system and the root system work together to follow Fick’s Law in order to thrive in the land environment. The roots increase surface area because they have many branching “hairs” that help the root absorb nutrients and water more efficiently from the soil (KF, Lecture). The vascular system helps aid the plant by increasing the concentration gradient. The xylem and phloem are transporting tissues that move nutrients and water up and down the root system by either the process of osmosis or cohesion. This consistent flow of nutrients increases the concentration gradient (KF, Lecture). The root system decreases distance to the cells because the root hairs are only one cell layer away from the vascular system therefore that decreases distance because of the proximity of the two (KF, Lecture). Fick’s Law has been supported as the key to survival because a variety of completely different organisms have evolved to develop traits that abide by this law. Therefore Fick’s Law is key to success for the survival of organisms.