chapter 5

MARKING SCHEME

Complete the events  in all stages in Mitosis and Meiosis.

MITOSIS

Stages	Events
Prophase	1.   Chromosomes become visible as they contract and shrink.     2.   Centrioles appear at opposite sides of the nucleus.     3.   Spindle fibres start to form.     4.   The chromosomes become shorter and fatter.     5.   It consists of two chromatids joined at the centromere.     6.   Nucleolus disappear     7.   Prophase ends with the breakdown of nuclear membrane
Metaphase	Chromosomes arrange themselves on the equator of the spindle
Anaphase	Chromatids separate at the centromere and migrate to opposite poles of the cell.  the centromeres leading.
Telophase	Chromosomes reach their destination. The cell starts to constrict across the middle. Nuclear membrane and nucleolus are reformed in each daughter cell. The spindle disappears. Chromosomes eventually regain their threadlike form and the cells return to resting condition. The daughter cell have the same chromosome constitution as the original parent cell.

MEIOSIS I

Stages	Events
Prophase I	1.       The chromosomes begin to condense. They become shorter, thicker and visible 2.       The homologous chromosomes come together to form bivalents through sinapsis process 3.       Each bivalent consists of a four-part structure called a tetrad. 4.       Tetrad consist of two homologous chromosomes. 5.       Non-sister chromatids exchange segments of DNA in a process known as crossing over. 6.       The points at which segments of chromatids cross over are called chismata. 7.       At the end of prophase I, the nucleolus and nuclear membrane disappear
Metaphase I	Pairs of homologous chromosomes align themselves on equator of spindle.
Anaphase I	Homologous chromosomes separate from each other and migrate to opposite poles of the cell
Telophase I	The chromosomes have  reached their destination The cell constricts across the middle as in mitosis. The spindle fibres disappear Nucleous and nuclear membrane for each group of chromosomes reappears

MEIOSIS II

Stages	Events
Prophase II	The nuclear membrane disintegrated The spindle fibres reform in each daughter cell
Metaphase II	The chromosomes arrange themselves on the equator of the spindle
Anaphase II	The centromeres divide and are pulled by the spindle fibres to opposite poles, carrying the chromatids with them
Telophase II	The chromatids uncoil and become indistinct The spindle fibres disappear The nuclear membrane and the nucleoli reform Cytokinesis occurs and four haploid cells are formed from one parent cell

Cytokinesis in Animal and Plant Cell

How cytokinesis happened in animal and plant cell?

Animal Cell	Plant Cell
Explanation: In animal cell, a cleavage furrow forms at the equator of the cell and deepens until the daughter cell separate.	Explanation: In plant cell, the Golgi apparatus buds off carbohydrate-filled vesicles that line up along the cell’s equator The vesicles fuse, producing the cell plate. The cell plate extends outwards to the existing cell wall, and separates the two daughter cells.

The Differences and Similarities between Mitosis and Meiosis

Complete  the table below:

Meiosis

Mitosis

                                                                    

 

Mitosis	Aspects/events	Meiosis
All somatic cells	Where it occurs	Reproductive organs
To replace damaged and dead cells	Purpose	To produce gamete
Pairing of homologous chromosomes (synapsis) does not occur	Synapsis	Homologous chromosomes pair up (synapsis) to form tetrads
Crossing over between non-sister chromatids does not occur during prophase	Crossing over	Crossing over between non-sister chromatids occurs during prophase I
The chromosomes are arranged randomly at the metaphase plate	Metaphase	Homologous chromosomes lineup side by side at the metaphase plate
Sister chromatids separate to move to the opposite poles	Anaphase	-Homologous chromosomes separate to move to the apposite poles -The sister chromatids still remain attached to each other
One	Number of division	Two
Two daughter cells	Number of daughter cells produced at the end of the division	Four daughter cells (gamete)
Diploid (2n) or the same number of chromosomes as the parent cell	Chromosomal number of the daughter cells	Haploid (n) or half the number of chromosomes of the parent cell
Genetically identical to the parent cell and to one another	Genetic content	Different from the parent cell and from each other
Does not cause genetic variation	Genetic variation	Causes genetic variation from one generation to the next
Produce cells for growth and repair	Role	Produce gametes

OBJECTIVE QUESTIONS:

1. B	6. B
2. B	7. C
3. A	8. C
4. D	9. A
5. D	10. D

STRUCTURED QUESTION:

1. (a) (i)  Cell Y

         (ii) For cell Y, synapsis/ homologous chromosome pairs/ crossover only occur in meiosis

    (b)     

                              

      (c)

                                      

       (d) Homologous chromosomes from cell Y go through crossover/genetic  material exchange but cell X does not go through change of genetic material.

       (e)  1.  From exchange of genetic material during crossover

             2. Free segregation of chromosomes, which are randomly arranged during metaphase I, produce different haploid gametes.

ESSAY QUESTION:

1. (a) - Cloning is a technique used to produce organisms or clones that are similar to the parent cell in all aspects.                                                    1

           - Cloning is a form of asexual reproduction because it is based on mitotic cell division                                                                                               1                                                                                                

           - The clones that are produced will have the same genetic content and chromosomal number with one another and with the parent cell.            1

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     (b)

Advantages of Tissue Culture	Disadvantages of tissue Culture
Cloned plants are uniform in size and shape Plants can be produced all the year around Plants maintain the same desired characteristics of the mother plant Tissue culture techniques are cost effective Clones can be produced in vast numbers in a short time	Clones are susceptible to new diseases Clones are easily destroyed if there is a change in the environment

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