Biology Issues: Carbon Cycles, Lizard Species, DNA Visibility - Scholarship Essay Example

1. Carbon cycles through the ecosystem between the atmosphere, organisms (such as producers, herbivores, and carnivores), and decomposers. This natural cycle maintains a somewhat constant level of carbon in the atmosphere. The burning of fossil fuels releases carbon into the cycle that has been trapped inside the earth. How does this affect the cycle and what problems can this cause Like most other objects in the universe, the Earth holds a great deal of carbon. In the natural carbon cycle, there are two main processes-photosynthesis and metabolism. During photosynthesis, plants use carbon dioxide and produce oxygen. During metabolism, oxygen is used and carbon dioxide is a product. The organic matter takes centuries to form. Fossil fuels principally consist of carbon and hydrogen bonds. There are three types of fossil fuels, which can all be used for energy provision- coal, oil and natural gas. The fossil fuel reservoir contains more than twice as much carbon as is now stored in forests and soils combined. When fossil fuels are burned carbon and hydrogen react with oxygen in air to form carbon dioxide (CO2) and water (H2O). Humans influence the carbon cycle during the combustion of any type of fossil fuel, which may include oil, coal, or natural gas. Burning fossil fuels is responsible for many environmental issues such as greenhouse gas accumulation, acidification, air pollution, water pollution, damage to land surface and ground level ozone. The amount of carbon dioxide and other green house gases in the atmosphere is getting greater. This may trap more infrared radiation, and make the atmosphere warmer. This is called the enhanced green house effect and its possible effect on the Earth's temperature is called global warming. Currently, oil burning is responsible for about 30% of all carbon dioxide emissions to air. During combustion in the presence of air, carbon dioxide and water molecules are released into the atmosphere. There is so much more carbon stored in fossil fuels than in the air. Therefore, burning these reserves that releases carbon directly to the air in the form of carbon dioxide can bring about some very large changes in atmospheric CO2, especially if it occurs on a time scale that is faster than that of the natural removal processes. Some scientists predicts that each doubling of atmospheric CO2 should produce an increase of 1.5 to 5C (about 3 to 9F) in the mean surface temperature of the Earth, so three of them could drive the temperature 4.5 to 15C higher than what it is today. Another effect of increase in carbon emission due to burning of fuel is the rise in sea level that would likely follow. A warming of 3-10 or more in the mean temperature of the Earth implies a larger change in surface temperature at higher latitudes. This will likely melt some of the polar ice and add to the more certain rise in sea level and consequently many low-lying areas of the land may be flooded. If we consume a large fraction of the fossil fuels that today remain beneath the ground, atmospheric CO2 levels will almost certainly increase by very large amounts, and as a result, the surface temperature of the Earth will warm significantly during the next several centuries. A rise in temperature would also affect the climate in many parts of the world. No one is sure just what would happen where-there are too many variables for scientists to be able to predict the consequences. 2. Using Darwin's reasoning, explain how four species of lizards, all closely related, came to be separate species on a Caribbean island. Charles Darwin put forward his theory of evolution in a book called The Origin of Species, which was published in 1859. His theory can be summarized in the following principles. Variation- most populations of organisms contain individuals, which vary slightly from one another. Over production-, most organisms produce more young than will survive to adulthood. Struggle for existence-Because populations do not generally increase rapidly in size there must therefore be considerable competition for survival between the organisms. Survival of the fittest- only the organisms that are really well adapted to their environment will survive. Advantageous Characteristics passed on to offspring- Only those well-adapted organisms will be able to reproduce successfully, and will pass on their advantageous characteristics to their offspring. Gradual change- In this way, over a period of time, the population will lose all the poorly adapted individuals. The population will gradually become better adapted to its environment. (Johns Mary, Johns Geoff (1995). Charles Darwin was an acute observer and naturalist. He observed some species of lizards on a Caribbean island concluded that, perhaps only a few individual lizards originally landed on an island. Since there was no competition, the lizard population quickly grew, and different groups of lizards began to inhabit different niches, living in separate areas of the habitat and eating different food items. Over time, they became separate species. 3. During interphase, the DNA is not visible through a microscope; it only becomes visible as chromosomes during mitosis. Why isn't the DNA visible during interphase and why would this be the case Each chromosome is made of one long piece of DNA. The chromosomes in our own cells are millimeters in length, i.e., thousands of times longer than the diameter of a human cell nucleus. Thus, the DNA of each chromosome must be condensed many fold to make an object that is small enough for the cell to move it around in an organized fashion. The "condensation" of each chromosome is achieved in part by wrapping the DNA around small clusters of proteins. This hierarchy of condensation shortens the DNA of each chromosome the necessary thousands of fold, making an object that is short enough to fit easily into a nucleus and is nearly invisible through a microscope. DNA must be extended during interphone, so it can serve as a template for both RNA synthesis and DNA replication. As DNA replicates, the two identical double stranded molecules that are produced become linked together. Therefore, the two copies will be connected as they go into mitosis. Every chromosome condenses in preparation for cell division during the stage of the cell cycle called "prophase". It interacts with the now almost fully condensed chromosomes and organizes them into the 2-fold symmetric structure seen in "metaphase", the stage just before the separation of the duplicated chromosomes. 4. How is it that, in meiosis, you can end up with four "daughter cells" that are all genetically different from one another There are two kinds of cell division: mitosis and meiosis. Mitosis is essentially a duplication process: It produces two genetically identical "daughter" cells from a single "parent" cell. You grew from a single embryonic cell to the person you are now through mitosis. Even after you are grown, mitosis replaces cells lost through everyday wear and tear. The constant replenishment of your skin cells, for example, occurs through mitosis. Mitosis takes place in cells in all parts of your body, keeping your tissues and organs in good working order. Meiosis, on the other hand, is quite different. It shuffles the genetic deck, generating daughter cells that are distinct from one another and from the original parent cell. Although virtually all of your cells can undergo mitosis, only a few special cells are capable of meiosis: those that will become eggs in females and sperm in males. So, basically, mitosis is for growth and maintenance, while meiosis is for sexual reproduction. Separation of chromatids occurs as a result of the second meiotic division, and give rise to four daughter cells, each containing a haploid set of chromosomes (1n; 1c) amount of Meiosis occurs in the germ cells. As a result of meiosis, four daughter cells or gametes are produced, each containing one of a pair chromosome and all containing different chromosomes. The equation of the division is physically the same as mitosis, though the genetics of the cells are different. This time, there is only one member of each homologous pair to separate as sister chromatids into the newly formed cells. As a result, four non-identical new daughter cells are produced.Two cell divisions usually result in four progeny cells that are not genetically identical. Daughter cells are haploid and have half the chromosomal complement of the original diploid cell as the result of the separation of homologous pairs during anaphase .Crossing over in prophase I and separation of homologous pairs during anaphase I produce daughter cells that are genetically different from each other and the original cell. 5. Your friend Gorinda wants to know if there are ever mutations that don't cause problems. What do you tell him Accidental changes in DNA produce mutations. Almost everything that happens in a living organism is controlled by DNA. But occasionally things do go wrong. Sometimes it can happen during meiosis. It can even happen in the DNA molecule itself. Most mutations are harmful. Some mutations might code for a different amino acid, resulting in a final protein that actually works better, or faster, than the original, and so would be a positive mutation. There are many examples of mutations that are beneficial to people: seedless grapes, short-legged sheep, hairless dogs, but these would all be harmful to the organism in its own environment and, hence, harmful in evolutionary perspective. For example, there are people with mutations in the CCR5 gene that make them virtually immune to HIV. The effects of mutation vary depending upon the environment. People carrying homozygous mutated CCR5-delta 32 are resistant to HIV, while heterozygous ones are beneficial, as it slows down the disease progression. Thus, CCR5-delta 32 provides partial or complete immunity to HIV. Similarly, it is a beneficial mutation against other chronic diseases. There is no doubt that some of the most productive plants and animals are evolved because of mutation. The effects of mutation are well explained by natural selection in which favorable changes remain in the population, while those harmful alterations are eliminated over a period. 6. Use Punnett squares to illustrate whether a type A female and a type B male can have a child with type O blood. The standard way of working out what the possible offspring of two parents will be is the Punnett Square. A Punnett square is a simple graphical way of figuring out how the genes from each parent might combine to produce an offspring. The Punnett square duplicates the observation that the reproductive cells (eggs and sperm) get only half the normal number of chromosomes. When an egg is made, it receives one of each pair of chromosomes, not both. It is also the case with sperm. Since eggs and sperm each carry only one of each chromosome instead of a pair of each, they carry only one copy of each gene instead of two. This is the basis of the Punnett square - line up the possible reproductive cells for one parent along the top of the square, and the possible reproductive cells for the other along the left side of the square, then combine them in the middle to show all possible combinations of alleles of this genes from the two parents that may occur in their offspring. A woman with type A blood could have the genotype of IA I A or the genotype IA i. A man with type B blood could have the genotype of IB IB or the genotype IB I. If both of them were heterozygous for blood type, then the cross would be IA i. X IB I. They would have a 1 in 4 chance of having a child with blood type O. 7. A very heavy rainstorm floods a mountain river, changing its course and digging a deep canyon through the soft soils of the meadow in the valley below. What happens to the mice on either side of the valley The mice would leave the valley due to this geographical impediment eventually there would be interbreeding. They will go their separate ways and reproduce to make two populations of mice on either side of the valley. There are just too many mice and too little time for them to evolve into anything different from each other. If we put evolutionary reasoning to it, the original mice population may have split unevenly so that more mice with certain characteristics are on one side of the valley than the other side. The physical boundary restricts gene flow between the two separate populations, as they are no longer able to reach each other to reproduce. This creates two different gene pools for the two populations. Environmental conditions may also differ in the two sides of the valley so that organisms with a certain characteristics at a selective advantage compared to those without the characteristic. If the conditions are different then the surviving mice on the two sides of the valley may differ. This causes genetic drift so that the two gene pools become very indifferent and the changes are so vast that they change the an anatomy of the reproductive structures in both mice, they become two different species and will never be able to interbreed again with the mice on the other side of the valley. To put it briefly, it will lead to an allopathic speciation, which is due to a physical barrier that splits a single population into two separate gene pools, allowing speciation to occur. References Alfred, Cushier. Gemetogenesis. Retrieved from http://staff.um.edu.mt/acus1/GAMETGENESIS.htm. Charles E, Ophardt. ( 2003). The CarbonCycle. Retrieved from http:// www. elmhurst.edu/ chm/ vchembook/306carbon.html James F. Kasting, (2005). The Carbon Cycle, Climate, And The Long-Term Effects Of Fossil Fuel Burning. U.S Global Change Research Information Office. Retrieved from http://www.gcrio.org/CONSEQUENCES/vol4no1/carbcycle.html Johns, Mary., Johns, Geoff. (1995). Biology. Cambridge, UK: Cambridge University Press. Mackean, D.G.(1986).GCSE Biology (Third Ed.. London: John Murray. Mishra, C.S. (2002). Super Simplified Science and Technology (Biology). New Delhi: S. Dhinesh & Co. Miller, G.T. (1999). Living in the Environment: Principles, connections and solutions (Fourth edition) Pacific Grove, USA: Brooks/ Cole Publishing Company. Morris,Paul J. (1999) Athro. Retrieved from http://www.athro.com/evo/gen/punnett.html Parker, Gary.(2009) Mutations. answeringgenesis.org. Retrieved from http://www.answersingenesis.org/home/area/cfol/ch2-mutations.asp Read More