WELCOMERESHMA THANKAPPANBEd NATURAL SCIENCEROLL NO:34

THE MYSTERY OF GROWTH

Living beings are characterized by their ability to grow

Development of organism from the zygote to the fully

grown state taken place by mitosis, this is known as

growth

When a cell attains particular size, it divides

MITOSIS

It is discovered by Flemming in1882

It occurs in somatic cells, so it is called somatic cell

division

During mitosis a cell divides due to two identical

daughter cells ,so it is called as equational division

The divided cells will have nucleus having the same

amount of DNA as the parent cell

TYPES OF MITOSIS

INTRANUCLEAR MITOSIS

It occurs in acellular organism

Nuclear membrane remains intact and mitotic events occurs

within the nuclear envelope

Nucleus divides along the cytoplasm

EXTRANUCLEAR MITOSIS

Nuclear membrane break

Mitotic events occur within the cytoplasm

ANASTRAL MITOSISMitosis without asters is called anastral mitosis

ASTRAL MITOSISMitosis with the appearance of asters is called astral

mitosis

ENDOMITOSISThe multiplication of chromosome without nuclear

division

The life history of a cell called cell cycle The two important phases of cell cycle are:

1.Interphase

2.Mitotic phase

INTERPHASE

It is also known as resting phase

It is considered as the first phase of mitosis

The interphase consist of 3 sub stages: G1, S and G2

During interphase RNA, protein are synthesised,cell organells are

produced,DNA duplication and spindle fibre formation are occur

MITOTIC PHASE

During mitotic phase the duplicated materials are

separated

It takes place in different phase,they are:

1.prophase

2.metaphase

3.anaphase

4.telophase

PROPHASE

Chromosomal materials condences to form

compact mitotic chromosomes

Chromosomes composed of two

chromatids attached together at the

centromere

Initiation of the assembly of mitotic

spindle, the microtubule, the proteinaceous

components of the cell cytoplasm help in the

process

METAPHASEThe complete disintegration of nulclear

envelope occur in this phase

Spindle fibers attach to kinetochores

of chromosomes

Chromosomes are moved to spindle equator

and get alligned along meataphase plate

through spindle fibres to both poles

ANAPHASE

chromatids of each chromosomes are separated and

form two chromosomes called daughter chromosomes

The daughter chromosomes move towards the opposite

poles of the cells

The migration is achieved by the contraction

of the chromosomal fibres and

streching interzonal fibres

TELOPHASE Nuclear membrane and nucleolus reappear,

spindle fibres disappears Golgi complex and endoplasmic reticulam

are reappeared

CYTOKINENSIS

It is as end stage of cell division

Cell plate is developed between two daughter nuclei

SIGNIFICANCE OF MITOSIS

It ensures equal distribution of the nucleus and the

cytoplasm between the daughter cells

The chromosome number is maintain constant

It helps in the growth and development of the organ and

the body of the organisms

It helps in the asexual reproduction in the organism

It helps in the repair of tissues

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