Biology Essay Examination essay

With the general notion and belief that the carbon levels in the atmosphere are maintained at constant levels in normal conditions, the continuous increase of carbon levels because of human actions will definitely bring changes to the carbon cycle and become causative to the development of potential repercussions to the ecosystem. For one, plants and microorganisms may develop changes in the way metabolic processes are prioritized.

For one, the rate of decomposition by microorganisms will be significantly enhanced by the increased supply of carbon in the soil; plants on the other hand may also be enhanced in terms of growth. However keeping in mind that carbon levels also affect the temperature, then some plants may even become extinct due to elevated carbon levels through the alteration of terrain (Millennium Ecosystem Assessment [MEA], 2005).

Indeed, alterations in the carbon cycle through a significant increase in carbon levels worldwide result in a variety of effects, which as pointed out include temperature increase. Hence, its effects on the ecosystem in general may be varied depending on the location. In fact, while in other areas the ecosystem may be significantly affected because of the loss of primary producers; in other areas the rise of carbon levels may lead to the development of more habitable areas from previously hostile environments such as in ice filled locations (MEA, 2005).

As the carbon cycle will no longer be able to maintain a balanced level of carbon, due to the overabundance of carbon in carbon reservoirs (MEA, 2005), changes will definitely occur in the ecosystem which might possibly alter the distribution of organisms as well. Darwinian Reasoning In the concept of evolution, the main assumption made is that there are several factors, collectively known as agents of natural selection, which affect the changes that occur on organisms (Purves et. al. , 2003). In this sense, different forms of environmental pressure, may or may not favor certain parts of the population.

For example, if a drought occurs and wipes out most vegetation that a certain herbivore feeds upon, and the only edible vegetation left are those that requires additional stature or height, then it is highly possible that only those with the appropriate physical characteristics for the task may survive and remain to represent the population. This of course, takes into consideration that even though a population may contain a single type of species, variations are still abundant because of the presence of variation based on inherited characteristics (Purves et.

al. , 2003). Such a process, mainly explains why four closely related species of lizards in the Caribbean was mainly developed from the same ancestral species. Adding on the basic points considered in the theory of evolution, Darwin also explained the possibility of divergent forms of evolution to occur. Specifically, divergent evolution pertains to the branching out or differentiation and development of species that are basically originally from the same species due to the presence of environmental factors for selection (Alford and Hill, 2003).

In this sense, the ancestral lizard, which as previously discussed probably has variations based on genetic differences, may have been exposed to different opportunities or possibilities for food gathering for example. In this sense, as a single food source may not be able to satisfy the needs of the population, the lizards with different characteristics better suited for a different food source may have begun to move out and focus on the said sources wherein their characteristics are better suited.

Eventually, the adaptations for each of the four groups may have been further defined, and after several generations have completely developed into distinct species. DNA Visibility Through microscopy, the DNA may be observed as chromosomes in mitosis. However, it is evident that during interphase, which is generally considered as a significant step in the cell cycle along with mitosis, the DNA is not observable under similar means of microscopy. In order to understand this, it is important that the underlying processes under the interphase are taken into consideration.

In the interphase, specifically in its sub-phases which are G1, S, and G2, the DNA is continuously processed and increases in number through synthesis and replication (Purves et. al. , 2003). However, a direct aggregation and organization of the DNA is significantly lacking in the sub-phases of the interphase which may be causative to the fact that the DNA is not microscopically observable during the underlying phases of the interphase. To expound, during the steps in mitosis, spindle fibers are developed along which the reorganization of the chromosomes throughout the cell occurs.

Throughout mitosis, the efficient polarization of the chromosomes and the arrangement of the spindle fibers requires that a chromosome must contain more than a single DNA unlike in the interphase in which the chromosome and the DNA are merely at a one is to one ratio and is quite dispersed (Purves et. al. , 2003). In this sense, the reason as to why the DNA becomes microscopically observable during mitosis is mainly due to the packaging process of the chromosomes.

In order to efficiently accommodate such a long structure in the cell, continuous coiling and condensation occurs throughout mitosis until the cell divides (Purves et. al. , 2003). Hence, the main reason behind chromosomes becoming observable during mitosis and not during the interphase is merely due to the condensation that occurs which increases its visibility. Daughter Cells Meiosis, a characteristic of eukaryotic organisms, in which sexual means of reproduction are made possible, in which the four daughter cells produced are made distinct by the fact that each has a unique genetic characteristic.

In order to comprehend the reason as to why meiosis results into creating four genetically different daughter cells requires that the processes and phases in meiosis is assessed. In prophase I, through the the process of synapsis two pairs of chromosomes are formed, both consisting of both a maternally derived and a paternally derived chromosome (Purves et. al. , 2003). The main reason for genetic differences between the daughter cells relies upon the stage following prophase I, which is metaphase I. Although in prophase I, a process of pairing is observed, its process does not require specific alignments.

In metaphase I, the chromosomes are aligned along the equatorial area of the cell through the aid of the microtubules; the process of alignment requires that a randomized event of crossing over occurs in which parts of the chromosomes may become interchanged (Purves et. al. , 2003). In this sense, if the initial reason as to why genetic distinction is created has been established. However, the chromosomes still occur as pairs at this point. In telophase II, the separation into four distinct cells is initiated. In fact, at this point each division requires and contains only parts of a single chromosome derived from assortment (Purves et.

al. , 2003). In this sense, it is made clear that the occurrence of four genetically distinct daughter cells is based on the subsequent division and crossing over of the chromosomes throughout the steps or phases during the process of meiosis. Harmless Mutations Mutations are often associated with harmful effects such as serious diseases and even death. However, not all are aware of that there are different types of mutations which result in various forms of substitutions which result into different changes in the DNA.

For example, missense mutations which are basically the result of an altered base which develops into changes in terms of the protein coded for, are known to cause both sickle-cell anemia and cystic fibrosis (Kimball, 2008). Another kind of mutation is known as nonsense mutations. Similar to missense mutations, nonsense mutations are able to cause harmful effects such as failure in terms of specific biological processes through the occurrence of premature termination (Kimball, 2008).

Unlike those previously mentioned, silent mutation is generally known to be incapable of causing harm towards individuals. Due to the fact that proteins are not essentially coded for by a single sequence but rather possibly coded for by several combinations, then some changes in terms of the bases may not result in any changes in terms of the proteins coded for (Kimball, 2008). In this sense, no apparent changes will be done in terms of the resulting product, hence it will function in exactly the same manner as the one coded for the by original unaltered sequence.

In fact, in order to determine the occurrence of such mutations, a complete genetic analysis must first be performed (Kimball, 2008). Egg Cell It is quite amusing to think that scientists would be able to shock egg cells so as to initiate cell division similar to what occurs during the earliest stages of development. However amusing this may be, it is rather impossible for scientists to achieve such a feat because of two main reasons in relation to the process of fertilization which are metabolic initiation and diploid formation.

Of course, one of the main functions of the contact between the two gametes is to initiate or begin the process not only of the increase in cell number but also in terms of changes in orientation. Specifically, the entry of the sperm into the egg cell results in a cascade of metabolic effects, along with specifically laying out the pattern in which the development of the embryo will be based upon (Purves et. al. , 2003). Critics might of course say that artificial means of achieving such effects may be present, definitely though using shock in order to complete the chromosome is highly unlikely.

As a matter of fact, the process of fertilization allows for the haploid gametes to form the complete diploid individual (Purves et. al. , 2003). Hence, the complete functional process of cell division and its results, which also entails and requires the process of DNA synthesis and replication, along with chromosome recombination to occur cannot be simply achieved by shocking the egg cell. Plant Growth Plants are considered to be capable of rapid growth and reproduction, in relation to the capability to derive energy from an abundant source which is the sun.

However, it is rather evident that plant overgrowth up to an extreme extent, in which individuals may need to walk through piles of dead plants each day, is an unlikely scenario. The reason for this is that there are regulators for plant development. In terms of the self limiting capabilities of plants, it is important to take note that plant growth is innately regulated through the action of plant hormones and photoreceptors (Purves et. al. , 2003). Plant hormones, act as regulators for growth by in part dictating the developmental process of the plant.

Specifically, plant hormones such as gibberillins, ethylene, auxins, and cytokinins, control or regulate the extent of several points throughout plant growth including stem and root growth, seed formation, and fruit ripening (Purves et. al. , 2003). Hence, the overgrowth of plants and the rapid movement through different growth phases are maintained at a normal level by such hormones. As pointed out, photoreceptors are another way in which plants may regulate their growth. A common example of regulation through the action of photoreceptors is the pattern through which seeds germination occurs.

As the seed is buried underground, the main movement of development for the developing plant is to move towards the nearest source of light (Purves et. al. , 2003). It is important to note that both hormones and photoreceptors are controlled and maintained through the same process. To expound, signal transduction pathways, similar to those present in animals, mainly facilitate the processing of the signal at the receptor until a biological response is attained (Purves et. al. , 2003).


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