ZOO503 Assignment Solution Fall 2019

    
ZOO503 Assignment Solution Fall 2019





Assignment No. 1

ZOO503 – Zoogeography and Paleontology

Fall 2019

 

                                                                                                       Total Marks: 5
                                                                                                                Due date: 30-11-2019
Instructions:
·      Make sure that you upload the solution file before due date. No assignment will be accepted through e-mail after the due date.
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     Solution guidelines
·      To solve this assignment, you should have good command over lectures 1-45.
·      This is not a group assignment, it is an individual assignment so be careful and avoid  copying others’ work
·      Give the answer according to question only and avoid irrelevant details (not consisted of more than two pages).

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Question
                                                                       
            “The origin of life: Evidence for the origin of life”                                                (05)                                                                                                                  

Chromosomes,the Cell Cycle, and Cell Division


In 1951, 31-year-old Henrietta Lacksentered Johns Hopkins Hospital to be treated for a cancerous tumor. 
Although she died a few months later, her tumor cells are still alive today. Scientists found that, given adequate nourishment, cancerous cells from the tumor could reproduce themselves indefinitely in a laboratory dish, where they grew as a formless mass.
 These “HeLa cells” became a test-tube model for many studies of human biology. Over the past half-century, tens of thousands of research articles have been published using information obtained from Henrietta’s cells. But are these “immortal” cells really a good model for human biology? In one sense, they are indeed a good model. Most multicellular organisms come from a single cell: the fertilized egg. 
This cell reproduces itself to make two cells, which in turn divide to become four cells, and so on until all the cells of a new organism have been produced.
 An organism is not just a mass of cells like the HeLa culture, however; its cells must form specialized tissues and organs, each with specific roles to perform. In normal tissues, cell reproduction (cell “births”) is offset by cell loss (cell “deaths”). 
We know that cell death is important from careful studies of a tiny worm, Caenorhabditis elegans, in which 1,090 cells are produced from the fertilized egg and exactly 131 of them die before the worm is born. If the cells that are programmed to die do not do so, the worm’s organs are severely malformed.
 Another example occurs in the mammalian brain. Young mice, for instance, lose hundreds of thousands of brain cells each day; if these cells do not die, the mouse’s overcrowded brain simply does not work. Acell’s death is often programmed into its genetic instructions:

In this chapter, we will first describe how prokaryotic cells produce two new organisms from the original single-celled organism.
Then we will describe two types of cell and nuclear division—mitosis and meiosis—and relate them to asexual and sexual reproduction in eukaryotic organisms.
In this chapter, we will first describe how prokaryotic cells produce two new organisms from the original single-celled organism.
Then we will describe two types of cell and nuclear division—mitosis and meiosis—and relate them to asexual and sexual reproduction in eukaryotic organisms.
 Finally, to balance our discussion of cell proliferation through division, we will describe the important process of programmed cell death, also known as apoptosis.

Systems of Cell Reproduction :
Unicellular organisms use cell division primarily to reproduce themselves, whereas in multicellular organisms cell division also plays important roles in growth and in the repair of tissues . In order for any cell to divide, four events must occur:
 There must be a reproductive signal.
This signal, which may come either from inside or outside the cell, initiates the cellular reproductive events.  Replication of DNA (the genetic material) and other vital cell components must occur so that each of the two new cells will be identical and have complete cell functions. 
The cell must distribute the replicated DNA to each of the two new cells.
 This process is called segregation.
 New material must be added to the cell membrane (and the cell wall, in organisms that have one) in order to separate the two new cells in a process called cytokinesis. 





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