• Describe the 4 stages of mitosis• Explain the behaviour of chromosomes at each stage• Describe briefly about cytokinesis• Compare the cell division in animal & plant cell• State the significance of mitosis

OBJECTIVES

12.3 MITOSISDefinition

a process by which …… a cell nucleus divides

to produce two daughter cells; each contain the identical number of chromosomes to the parent cell

… is followed by cytokinesis

12.3 MITOSISThe Phases

two main phases in mitotic phase: Karyokinesis; the division of nucleus Cytokinesis; the division of cytoplasm

four stages of karyokinesis:

1.prophase2.metaphase3.anaphase

4. telophase

12.3 MITOSISLate interphase: chromosomes have been

duplicated in the form of chromatin

fibers centrosomes have been

duplicated microtubules extend from

centrosomes to form aster

Early Prophase: Chromatin densely

coiled & folded ; become shorten & thicken (condense)

Each chromosome exist as a pair of sister chromatids attached together at centromere

Nucleoli disappear and nuclear envelope

disintegrates

Mitotic spindle (spindle fibers) begins to form …‘pull’ the centrosomes toward the opposite

poles of the cell

Late prophase Microtubules of spindle fibers extend toward the

middle of the cell Kinetochore microtubule attach to the

kinetochore of centromere Nonkinetochore microtubule from one pole of

the cell interact with nonkinetochore microtubule from the opposite pole

kinetochore (chromosomal) microtubules

nonkinetochore (polar) microtubules

Metaphase Centrosomes are at

opposite poles of the cell

spindle fibers pull the chromosomes until they are all alligned at metaphase plate

i.e. imaginary plane that is equidistant between the two poles

Anaphase centromeres divide chromosomes are

pulled to the opposite poles as kinetochore microtubule shorten

the separated chromatids (now called chromosomes) are pulled behind centromeres

both poles have equivalent number of chromosomes

Telophase

nucleoli and nuclear envelope re-form

chromosome becomes uncoiled, lengthen and can’t be seen (in the form of chromatin)spindle fibers disintegrate

cytokinesis begins

Cytokinesis the division of cytoplasm usually follows

telophase

12.3 MITOSIS

in animal cells cleavage furrow is formed

on the cell surface at the old metaphase plate

cell membrane invaginate forming furrow that’ll join up and splits the cell into two

in plant cells In the centre of the cell, Golgi body produce small

fluid-filled vesicles The vesicles fuse to form cell plate The contents of the vesicles is used to form the

new cell walls of the daughter cells The plate enlarges until its fuses with the parent

cell wall and separates the two daughter cells.

DIFFERENCES BETWEEN CELL DIVISION IN PLANT & ANIMAL CELL

PLANT CELL ANIMAL CELL• No aster is formed • Aster is formed• Kinetochore produce the spindle fiber

• Centriole produce the spindle fiber

• Cell plate is formed during cytokinesis

• Cleavage furrow is formed during cytokinesis

• Occur mainly in meristem tissue / cells• Cytokinesis begins from the center outwards

• Occur in cells / tissues throughout the body• Cytokinesis begins from the outer inwards

12.3 MITOSISSignificance / Importance

to facilitate growth and cell replacement Increase number of cells within an organism Replace die or damage cells

to facilitate asexual reproduction Bacteria, Amoeba, Paramecium and Euglena

reproduce by binary fission

to maintain the genetic stability produce 2 daughter cells that possess

identical number of chromosomes to each other & to parent cell