XI Biology Topic - Cell Division - Mitosis. Sturdy material for NEET, CET Exams. It includes phases of mitosis explained with images.

1. Cell Division
Tarini Joshi
M.Sc.,M.Ed.,NET,SET.

2. Cell Division
Cell division is imp for growth
and differentiation.
 The division is achieved by
Karyokinesis and cytokinesis.
 Differentiation of cell leads to
organ development.
 Organ into organism.
 Tissues like Bone marrow
,germinal tissue and
meristematic region divide
continuously.

3. Mitosis:
1. Mitosis was first observed by Strassburger
in plant cells (1870) and Boveri and Flemming
in animal cell ( 1879 ).
2. The term was coined by Flemming in 1882.
3. It is also known as equational division due
to equal distribution of chromosomes in
daughter nuclei.
4. It is often known as somatic cell division
due to occurrence in somatic cells.
5. It is about 1-5% of the total duration of cell
cycle.
6. On the basis of different types of cells and
the species, mitosis takes 30 minutes to 3
hours for completion.
Term mitosis was proposed by Flemming.
Mitosis produces genetically identical cells,
which are similar to mother cell.

4. Did You Know!!!
Some cell do not show
division .E.g. Heart cells
, Neurons.
Many cell divide
occasionally to replace
damaged cells

5. Prophase
1.It is longest phase of mitosis includes early and late
prophase
2. In Early phase involves condensation of chromatin
material.
3.Initially chromosome appears as thin and long
,chromatids attached by centriole.
4.Chromosomes undergo dehydration and becomes
short and thick.
5.In Late prophase The nucleolus starts to disappear.
6. Nuclear membrane disintegrates and disappears
gradually.
7. Centrosome which had undergone duplication during
interphase begins to move towards opposite poles of
the cell.
8. Mitotic apparatus is almost completely formed
9.Microscope which can be seen with its sister-
chromatids connected by centromere.

6. Metaphase:
1. In this phase, chromosomes are
completely condensed so that they
appear very short.
2. Sister-chromatids and centromere
become very prominent.
3. All the chromosome moves at
equatorial plane of the cell. This is
called metaphase plate.
4. Mitotic spindle is fully formed. With
the help of MTOC present in plants.

7. Anaphase:
1. Centromere of each chromosome divides
into two, each being associated with a
chromatid.
2. The chromatids of each chromosome
separate and form two chromosomes
called daughter chromosomes.
3. The formed chromosomes are pulled away
in opposite direction by spindle apparatus.
4. Chromosomes being pulled away appear
like a bunch of banana during midway of
anaphase.
5. Each set of chromosomes reach at
opposite poles of the cells marks the end
of anaphase.

8. Spindle fibres:
1.In animal cells the spindle fibers radiates an
aster from centriole and called as astral rays.
Hence astral mitosis
In plant cells aster absent hence anastral
mitosis.
2. Astral rays radiating from centriole to
periferi of cell.
3. Inter polar fibers- extending between
opposite poles
4. Chromosomal fibers- centromere to poles
5.Interchromosomal fibers- between
chromatids.

9. Telophase:
1. The telophase is the final stage of
karyokinesis.
2. The chromosomes with their
centromeres at the poles begin to uncoil,
lengthen and loses their individuality.
3. The nucleolus begins to reappear.
4. The nuclear membrane begins to appear
around the chromosomes.
5. Spindle fibers break down and get
absorbed in the cytoplasm.
6. Two daughter nuclei are formed in a
cell.

10. Cytokinesis:
1. The division of the cytoplasm into two
daughter cells is called cytokinesis.
2. In animal cell , The division starts with a
constriction. This constriction gradually
deepens and ultimately joins in the center
dividing into two daughter cells.
3. The division of cytoplasm is perpendicular
to the spindle.
4. In Plant cells, cell wall is present. Due to
this, furrow cannot be formed. Partition
starts to appear at the center of the cell and
grows outward to meet the existing lateral
walls.
5. The formation of the new cell wall begins
with 'cell-plate' that represents the middle
lamella between the walls of two adjacent
cells.

12. Significance of mitosis:
1. As mitosis is equational division, the chromosome number is
maintained constant.
2. It ensures equal distribution of the nuclear and the cytoplasmic
content between the daughter cells, both quantitatively and qualitatively.
3. The hereditary material (DNA) is also equally distributed.
4. It helps in the growth and development of organisms.
5. Old and worn-out cells are replaced through mitosis.
6. It helps in the asexual reproduction of organisms and vegetative
propagation in plants.
7. The process of mitosis also maintains the nucleo-cytoplasmic ratio.
8. Although mitosis is a very reliable process for preserving the genetic
make-up of cells or organisms, it cannot introduce variation or new
combination of existing genes.

13. DID YOU KNOW
• Death of cell:
• In many cases, that’s true: it's not good for cells to die because
of an injury (for example, due to scrape or a harmful chemical),
which is called necrosis.
• However, some cells of our body die; not randomly but in a
carefully controlled way.
• For example, during the embryonic development, the cells
between the embryonic fingers died in a process called apoptosis
to give a definite shape to the fingers. This is a common form of
programmed cell death.
• Apoptosis involves the cell death, but it benefits the organism as
a whole (for instance, by letting fingers develop or by eliminating
potential cancer cells).

14. Questions
• What is Mitosis?
• Mitosis takes place in………. cells
• chromosome number in mitotic daughter cell….. of parent cell
• Nucleolus reappears in …… stage.
• Explain in detail phases of Mitosis.
• Sketch and label phases of mitosis.

15. References –
NCERT Textbook of Biology
H.Sc. Textbook of Biology
https://www.google.com/images