Chapter 5 with ans

Chapter 5: Cell Division

Important terms and concept

1. Haploid – Cell with single set of chromosome (n)

2. Diploid – Cell with complete sets of chromosomes (2n)

3. Cell division:

a) Mitosis – 1 parent cell (2n) 2 identical daughter cells ( 2n )

b) Meiosis – 1 parent cell (2n) 4 different daughter cells ( n )

4.

5.1) Mitosis

1. 1 parent cell (2n) 2 identical daughter cells ( 2n )

2. It is part of the cell cycle (Interphase Mitosis Cytokinesis)

3. Interphase is divided into:

a) G1 phase Growth of cell by producing proteins and organelles

b) S phase Synthesis / duplication of DNA (thread-like chromatin)

c) G2 phase Growth of cell by producing proteins and organelles

4. Mitosis is divided into prophase, metaphase, anaphase and telophase

1 © Gabriel Chua, 2013

chromatid sister chromatid

chromosome chromosome

homologous chromosome

Prophase Chromosomes start to appear and condense as 2 identical chromatids

Nuclear membrane disintegrate and nucleolus disappear

Centrioles move apart to opposite sides Spindle fibre begins to form

Metaphase Chromosomes move to cell’s equator Chromosomes line up at cell’s equator with centromeres

attached to spindle fibre Each chromatid faces its own pole

Anaphase Chromosomes divide into two Each sister chromatid separate and move to opposite

poles When the chromatids reached its own pole, they become

independent chromosomes

Telophase There are now 2 sets of chromosomes, one at each pole Chromosomes become thread-like structures Spindle fibre disappear Nuclear membrane begins to form around both sets of

chromosomes Nucleolus reappears Cytokinesis begins

5. Cytokinesis in animal cells is by forming cleavage while that of plant cells is by forming

cell plate.

6. Importance of mitosis

a) Repair damaged cells and replace dead cells

b) Asexual reproduction in unicellular organisms

c) Preserve diploid number of chromosome

d) Ensure new cells are identical to parent cells


7. Application of mitosis

a) Repair damaged cells and replace dead cells

b) Tissue culture

c) Clonnnig

d) Uncontrolled mitosis causes cancer

5.2) Meiosis

1. 1 parent cell (2n) 4 different daughter cells ( n )

2. Meiosis is divided into:

a) Meiosis I b) Meiosis II Prophase I Prophase II Metaphase I Metaphase II Anaphase I Anaphase II Telophase I Telophase II

Prophase I Chromosomes thickens and condense Each chromosome consists of 2 sister chromatids Homologous chromosomes pair together (bivalent) via

synapsis The criss-cross between homologous chromosomes is

known as chiasmata This results in genetic variation Centrioles move to opposite poles Spindle fibre forms Nuclear membrane and nucleolus disintegrate

Metaphase I Paired homologous chromosomes line up at cell’s equator

Each chromosome are attached to spindle fibre at centromeres

Each chromosome faces its own pole

Anaphase I Paired homologous chromosomes separate from each other and move to opposite pole


Telophase I Chromosomes reached its own pole Each pole has haploid chromosome set Spindle fibre disappear Nuclear membrane and nucleolus reform Cytokinesis begins

3. Meiosis II is the same as mitosis

4. Importance of meiosis

a) Allow trait inheritance in offspring

b) Maintain same number of chromosomes in each generation

c) Ensure production of haploid gametes in sexual reproduction

d) Produce genetic variation

Comparison between Meiosis I and Meiosis II

Meiosis I Meiosis IISimilarities

1. Consists of 4 stages, ie. prophase, metaphase, anaphase & telophase2. Involves division of nucleus and cytoplasm

DifferencesYes, at Prophase I Synapsis No

Yes, at Prophase I Crossing over No

In metaphase I, paired homologous chromosomes / bivalent / tetrad line up at equator

Metaphase

In metaphase II, sister chromatids line up at equator

In anaphase I, homologous chromosomes separate and move to opposite side

Anaphase I

In anaphase II, sister chromatids separate and move to opposite side

2 different daughter cells ( n )Number of daughter cells

4 different daughter cells ( n )


Comparison between Meiosis and Mitosis

Meiosis MitosisSimilarities

1. Both process are cell division process2. Chromosomes only replicate once

DifferencesReproductive cells Place occur Somatic cells

Parent cells divide twice Number of division Parent cells divide once

4 different daughter cells (n) Number of daughter cells 2 identical daughter cells (2n)

Yes, at Prophase I Synapsis No

2 Number of cytokinesis 1

Yes, at Prophase I Crossing over No

Each daughter cell has half the number of chromosome of parent cell

Number of chromosomes in daughter cells

Each daughter cell has the complete number of chromosome as parent cell

Genetic composition are different to parent cell or to each other

Genetic composition of daughter cells

Genetic composition are identical to parent cell and each other

Occurs during interphase before Meiosis I begins DNA replication

Occurs during interphase before mitosis begins

Produce gametes

Cause genetic variation

Reduce number of chromosomes to half

Role in animal body

Produce cells for growth

Asexual reproduction


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Chapter 5 with ans