Wednesday, 16 May 2012

CHAPTER 5 : CELL DIVISION


 Focus Practice 5.1 ( page 92 )

1.      Give two reason why mitotic cell division is important in living organism
·         Distributing an exact copy of each of their chromosomes to the new cells
·         For normal growth, development and maintenance
       
2.      Describe the process that takes place during the S phase.
·         Synthesis of DNA occurs during the S phase. The DNA in the nucleus undergoes replication. Each duplicated chromosome now consists of the two identical sister chromatids which contain identical copies of chromosome’s DNA molecule

3.      What is cytokinesis?
·         Cytokinesis is the division of the cytoplasm, occurs towards the end of telophase. 

4.      How does a normal cell change into a cancerous cell?
·         When a cell divides through mitosis repeatedly, without control and regulation, it produce cancerous cells.

Focus Practice 5.2 ( page 97 )


  1. State two differences between meiosis I and meiosis II.
   
            Meiosis 1
Meiosis 11
During prophase I, homologous chromosomes pair up and crossing over between non-sister chromatids occurs.
During prophase II, synapsis of homologous chromosomes and crossing over between non-sister chromatids does not take place
During metaphase I, homologous chromosomes align at the metaphase plate (equator) of the cell
During metaphase II, chromosomes align at the metaphase plate (equator) of the cell.
During anaphase I, homologous chromosomes separate and move to opposite poles. Sister chromtids are still attached together and move as a unit.
During anaphase II, sister chromatids separate, becoming daughter chromosomes that move to the opposite poles.
At the end of telophase I, two haploid daughter cells are formed. Each daughter cell has only one of each type of chromosomes; either the paternal or the maternal chromosome
At the end of telophase II, four haploid daughter cells are formed. Each daughter cell has the same number of chromosomes as the haploid cell produced in meiosis I, but each cell has only one of the sister chromatids.


  1. How is mitosis different from meiosis?
    • Mitosis which involves one nuclear division to produce two identical diploid daughter cells
    • Meiosis which involves two nuclear divisions to produce four haploid daughter cells which are not identical


  1. Explain how meiosis I reduces the number of chromosomes in the daughter cells?
During anaphase I, the spindle fibres pull the homologous chromosomes away from one another and move them to the opposite poles of the cell. This means each pole has only one member of the homologous chromosomes which is called haploid.

Focus Practice 5.3 ( page 97 )

  1. Why is it important for both mitosis and meiosis to occur in a controlled manner?
·         To prevent cancer and tummour

  1. What are the things that you can do to minimize the risk of getting cancer?
·         Balance diet
·         Regular exercise
·         No smoking and drink
·         Keep away from radioactive sources  

ASSESSMENT CHAPTER 5

SECTION A

1
A
2
C
3
B
4
D
5
A
6
C
7
B
8
C
9
D




SECTION B

  1. Figure 1 ( refer to page 100 )
a)      Q, R,T,P, S
b)     Plant cell –because no cleavage furrow/no centriole.
c)       -During cytokinesis, there are cell plate in a plant cell but not in the     
         animal cell.  Cleavage furrow is formed in animal cell to split the animal cell into two daughter cells.
-Most of the plant cells do not have centrioles but animal cell has.
                  d)  T (metaphase)- the centromeres of all the chromosomes are lined up on the
                                                  metaphase  plate. The two sister chromatids are still
                                                 attached to one another at the centromere. Metaphase ends
                                                when the centromeres divide.
                        P ( anaphase)-two sister chromatids of each chromosome separate at the
                                               centromere. The sister are pulled apart to the opposite poles
                                               by the shortening of the spindle fibres that connect the
                                               chromosomes to the poles.

  1. a ) anaphase
b ) P-spindle fibres
     Q-chromatid
c) 6

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