biology f4 c5n7

Group 7Stages Of

MitosisGroup member: Lee Kang Wenn,

Lai Siew Kee, Lin Sing Ka, Leonard Sie

Class: 4ATeacher: Pn Ko Hui Ing

What is Mitosis? Mitosis is a form of nuclear division

that produces daughter nuclei containing the same number of chromosomes as the parent nuclues. The daughter nuclei are genetically identical.

Mitosis results in 2 identical daughter cell

Chromosome

Chromosome

Chromosomes are made up of the molecule deoxyribonuclei acid (DNA). DNA stores all the information that a cell needs in order to grow and to carry out vital activities. This information is stored as sections of DNA or genes. The daughter cells produced by mitosis are genetically identical to the parent cell.

Onion Root Tip Slide

Stages Of Mitosis

Process of mitosis can be divided into 4 stages:

1) Prophase2) Metaphase3) Anaphase4) Telophase

The division is arbitary & whole process of mitosis is continuous.

ProphaseChromatin threads condense, coil and shorten to become chromosomes. Each chromosome consists of two sister chromatids attached at the centromere. The chromosomes are now visible under a microscope as x-shaped structures.

In an animal cell, structures called asters form around the centrioles. Asters are made of microtubules. The two pairs of centrioles move apart to opposite poles or ends of the cell. The nucleolus and nuclear envelope disappear. A spindle forms with the spindle fibres extending from one pole of the cell to the other.

Microtubules: Hollow protein structures found in the cytoplasm of cells.

Metaphase

Chromosome line up along the equatorial plane of the spindle. The centromere of each chromosome is attached on both sides to a spindle fibre.

Anaphase

Each centromere divides. The spindle fibres shorten and pull the chromatids apart to opposite poles of the cell. One the chromatids are seperated, they are called daughter chromosomes.

Daughter chromosomes

Telophase

Spindle fibres break down. A nuclear envelope forms around the chromosomes at each pole of the cell. A nucleolus reforms in each nucleus and the chromosomes uncoil and lengthen to become thin chromatin threads.

Chromatin threads

Nuclear envelope

Nucleolus

Cytokinesis

This is the division of the cytoplasm. In animal cells, cleavage or furrows appear in the cytoplasm between the two nuclei. The furrows deepen and two identical daughter cells are finally produced.

Mitosis in plant cells

Mitosis in plant cell is similar to that in an animal cell except that:- Centrioles are absent in a

plant cell.- Cleavage of cytoplasm does

not occur during cytokinesis. Instead, a cell plate is formed between the two daughter nuclei, dividing the cell into two. The cell plate is formed by the fusion of small fluid-filled vesicles produced by the Golgi apparatus.

Importance Of Controlled

Mitosis

Mitosis is important for the maintenance of the chromosomal set; each cell formed receives chromosomes that are alike in composition and equal in number to the chromosomes of the parent cell.

Mitosis occurs in the following circumstances:Development and growthThe number of cells within an organism increases by mitosis. This is the basis of the development of a multicellular body from a single cell i.e., zygote and also the basis of the growth of a multicellular body.Cell replacementIn some parts of body, e.g. skin and digestive tract, cells are constantly sloughed off and replaced by new ones. New cells are formed by mitosis and so are exact copies of the cells being replaced. Similarly, RBCs (red blood cells) have short life span (only about 4 months) and new RBCs are formed by mitosis.RegenerationSome organisms can regenerate body parts. The production of new cells in such instances is achieved by mitosis. For example, starfish regenerate lost arms through mitosis.Asexual reproductionSome organisms produce genetically similar offspring through asexual reproduction. For example, the hydra reproduces asexually by budding. The cells at the surface of hydra undergo mitosis and form a mass called a bud. Mitosis continues in the cells of the bud and this grows into a new individual. The same division happens during asexual reproduction or vegetative propagation in plants.

Effects Of Uncontrolled Mitosis

Although errors in mitosis

are rare, the process may

go wrong, especially during

early cellular divisions in

the zygote

. Mitotic errors can be especially dangerous to the organism because future offspring from this parent cell will carry the same disorder.

Cancer When mitosis gets out of

control, cells divisions are being made continuously, without an end point. As a result, this problem could lead to various types of cancer. If mitosis became uncontrolled tumor grows. Tumor, an abnormal mass of cells.

Cancer cells can intrude on and spread to other tissues which then lead to the malfunction of tissues and ultimately death.

Cancer cells compete with the surrounding normal cells to obtain sufficient nutrients and energy for their own growth.

THE END