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Cellular Reproduction

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Introduction

Cellular Reproduction Cellular Reproduction is the process by which all living things produce new organisms similar or identical to themselves. This is essential in that if a species were not able to reproduce, that species would quickly become extinct. Always, reproduction consists of a basic pattern: the conversion by a parent organism of raw materials into offspring or cells that will later develop into offspring. (Encarta, 2) In almost all animal organisms, reproduction occurs during or after the period of maximum growth. (Fichter, 16). But in Plants, which continue to grow through out their lifetime, therefore making the process more complex. Plants' reproduction is usually caused by a stimulant, mostly environmental or growth factors. The reproductive process, whether asexual or sexual always involves an exchange in hereditary material from the parent(s) so that the new organism may also be able to reproduce. Reproductive processes can be categorized in many diffrent ways although the most common is to put them into either asexual reproduction or sexual reproduction. Asexual reproduction is the process by which a single organism gives rise to two or more daughter cells. Most single celled organisms reproduce by the asexual process known as fission, which is commonly called mitosis. Fission (or Mitosis) is the division of one cell into two identical daughter cells. Interphase, the first phase of the cell cycle and also the phase before mitosis, starts as soon as the cell is born. Interphase is broken up into three phases, G1, S, and G2. ...read more.

Middle

Sexual reproduction is very significant, in that because of the fusion of two entirely different nuclei, the offspring could inherit an endless varied combination of characteristics, which may help improve the species. This is why organisms which reproduce sexually adapt quicker than do asexually reproducers. Multicellular plants alternate sexually and asexually reproducing generations. First, the plant starts as a gametophyte, which produces gametes. Then, it undergoes fertilization, and then mitosis, forming a sporophyte, which produces spores. When the sporophyte is ready to reproduce, it undergoes meiosis and produces spores. These form a gametophyte, and the cycle starts again and again until the plant dies. Pollination is the transfer of pollen from the male reproductive organ called the stamen, to the female reproductive organ, called the pistil. Pollination is not fertilization, which comes much later. The most common "helpers" with pollination are flying insects, which carry the pollen on their underside to the pistil, and the wind, which blows the pollen around in hopes that it might reach another plant. Since most ofd these plants have both male and female parts, the season in which the stamens release pollen is earlier or later to when the pistil is open to fertilization, preventing the plant from fertilizing itself. These plants have many ways to attract pollinators, some, while the pollinator (an insect) is landing, shoot up their stamens so some of the pollen could get onto the insect and hopefully pollinate another plant. ...read more.

Conclusion

In meiosis II, some cells have a short interphase in which the chromosomes do not replicate, in some other organisms, the cells go from late anaphase of meiosis I, to metaphase II, skipping telophase I, the short interphase, and prophase II. During Prophase II, the spindle forms in both of the newly born cells and the spindle fibers attach to the chromosomes. During metaphase II the chromosomes are yet again pulled to the "equator" of the cell. Anaphase II begins as soon as the centromere of each sister chromatid splits allowing them to move towards their poles. In telophase II, the nuclei reform, the spindles break down, and cytokinesis occurs. The end product of meiosis is very similar to Mendel's experiment in that there are sixteen different combinations for a zygote. Although meiosis usually goes ok, sometimes there is a mistake and chromosomes don't seperate correctly. This is called nondisjunction. There are three types of nondisjunction, Trisomy- when a gamete with an extra chromosome is fertiized with a normal gamete. Monosomy- when a gamete with one chromosome is missing and is then fertilized by normal gamete. And Trioloidy- where both zygotes have an extra chromosome. Reproduction is as essential to a species as food, water, or shelter. If a species cannot reproduce anymore, that species will eventually become extinct. There are many means of reproduction but primarily only two: asexual and sexual. In asexual reproduction, One organism gives a part or its whole self, in order to give rise to two or more new organisms. During sexual reproduction, two parents each form sex cells, which unite, and eventually form a new individual. ...read more.

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Response to the question

Response to the question is very in depth, but the response to the question could be set out in a much clearer way. The conclusion could be expanded a lot more to provide a more rounded view of the main ...

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Response to the question

Response to the question is very in depth, but the response to the question could be set out in a much clearer way. The conclusion could be expanded a lot more to provide a more rounded view of the main text. The introduction is adequate and sets out the main concepts of basic cellular reproduction well.

Level of analysis

Introduction is good and to a basic level, setting out the concepts of cellular reproduction well. The main body of the text goes into very in depth analysis to a level I would expect from an A level candidate rather than a GCSE one, with scientific concepts explained well. Rather than explaining all the different parts of meiosis, the candidate could analyse the different uses, and relate use to function. Conclusion is adequate but does not bring all the concepts explained into an strong conclusion. Could include diagrams and split up the text a lot more. Use of external sources is good.

Quality of writing

No paragraphs makes the essay very hard to read. Punctuation, grammar and spelling are all accurate and terms used are to a very high scientific level beyond what I would expect for GCSE level.


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Reviewed by skatealexia 19/03/2012

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