|
Cell
division 2. Notes and
diagrams to describe and explain the stages of cell division by mitosis
[Author
©
Dr WP Brown PhD:
Doc Brown's biology exam revision notes suitable for students of UK
IGCSE & GCSE level biology courses & ~ US grades 9-10 biology,
page on cell-division updated
Feb 10th 2026 *]
[Key
points and learning objectives for this page, after the main body of
notes]
Sub-index for biology notes on aspects of
cell division
[email doc b]
*
[privacy-policies-disclaimer] *
]SEARCH doc b's
science website]
(2) Cell division by
mitosis - the
details
Mitosis is the nuclear division giving rise to genetically identical cells
which is important for growth, repair of damaged tissues, replacement of cells
and asexual reproduction.
The precise duplication of chromosomes occurs before mitosis and during
mitosis, the copies of chromosomes separate, maintaining the chromosome number.
 In
the cell cycle
mitosis occurs during growth of new cells, replace damaged cells and asexual reproduction
in multicellular organisms.
In body cells the chromosomes are normally found in pairs and
that the chromosomes contain the genetic information.
Some organisms e.g. certain plants,
use mitosis to reproduce and is called asexual reproduction.
Cell division by mitosis
(diagram and notes below)
You can actually observe mitosis
in the school laboratory with a powerful
optical microscope.
In a fertilised egg, multiple
cell divisions occur by mitosis to produce all the huge number of
cells a complex living organism like ourselves needs to grow and
develop.
As an organism grows develops
the cells produced by mitosis must all contain the same genetic
information.
The genetic information is
found in the nucleus where the many long strands of DNA
aggregate together forming the chromosomes.
Most prokaryotes
like bacteria have a single circular chromosome, and
thus only a single copy of their genetic material.
Eukaryotes like us
humans, in contrast, tend to have multiple rod-shaped
chromosomes and two copies of their genetic material -
diagrams below.
There are 23 pairs of
chromosomes in human cells (diagram below) and they all have
characteristic shapes.
Each chromosome in a pair has
the same type of genes along its length and there are 46
chromosomes in total.
Diagrams (i-ii) of chromosomes from micrographs
(i) In the above diagram the
pairs of chromosomes are shown joined together by a centromere
during duplication to give the X shape.
(image adapted from shutterstock.com 701025034)
e.g. see the
details of cell division by
meiosis.
This profile of a human complete set of
chromosomes.
(ii) In this diagram the pairs of chromosomes are shown as
separate chromatids.
(image adapted from the US National Library of Medicine)
The 23rd pair are the sex
chromosomes, XY for male and XX for female.
(for more on this see
Genetics of Human Reproduction)
As already mentioned, new cells are
needed for growth and development and to replace worn out or damaged body
cells.
When new cells are formed they must be
identical to the parent cell.
When a parent cells split in two by
mitosis, two daughter cells are made.
The full sequence description
Interphase
==>
Prophase
==>
Metaphase
==>
Anaphase
==>
Telophase
==>
Cytokinesis
Acronym:
IPMATC =
I
Perform
Magic
And
Teach
Chemistry
(sorry about the latter
heresy on a biology page!, but it is all biochemistry really!,
however I'll leave it to you to decide on your own memory aid)
MITOSIS diagram shown below plus
text explanations
1.
The interphase.
Starting with the parent cell:
Prior to cell division,
in a cell that's not dividing, the
DNA is spread out in long strings within the very thin membrane of the nucleus.
Before the cell
can divide it has to grow and increase the number of sub-cellular
structures such as the mitochondria (respiration - energy source)
and ribosomes (from DNA to protein synthesis).
When the cell gets the
signal to divide, in the nucleus, the DNA must be copied (duplicated,
exactly to provide for 2 cells), and the result is double
chromosomes, mostly roughly X shaped.
Remember, to make two identical
cells, you need two lots of identical DNA and both V-sections of the
X-shaped arms of chromosome are identical (diagram 2.) - the right and left arms (each
half) of
the chromosomes are identical - an identical set of
genes.
At this point the original,
now duplicated DNA, is only about 1/50,000 thousandth of its
original length in the highly compacted chromosome of genes.
When the cell contents have been
copied the cell is ready to divide by mitosis.
Parts 2.
to 6. illustrate the actual cell division by mitosis
The actual mitosis can be described
in 4 stages - prophase, metaphase, anaphase and telophase.
2.
Prophase
The X shaped chromosomes condense, getting
shorter and fatter.
The nucleus membrane is
temporarily removed (breaks down) and the X-shaped chromosomes are free to move in the
cytoplasm.
3. Metaphase
The X chromosomes line up across the
centre of the cell.
(Note that the chromosomes are
only X shaped just before the cell divides.)
4. Anaphase
Simultaneously, very fine
cell fibres pull each X-shaped
chromosome apart into two identical sections (both V-shaped) which
are pulled to each end of the cell - these two clumps of chromosomes
will eventually form the nuclei of the two new cells.
5.
Telophase
The two sets of chromosomes collect together on
opposite sides of the cell and a nuclear membrane
forms around each set of chromosomes to form the nuclei of the two new
cells.
In other words the nucleus has split into two nuclei, but each
has complete copies of the DNA.
6. Cytokinesis
Finally, before the telophase
finishes, the cytoplasm divides in two
(process called cytokinesis) with both sections surrounded by
its own cell membrane to give two
genetically identical diploid cells - sometimes referred to as
'daughter cells' - which are genetically identical to the parent cell
- in humans, all will have a full set of 46 chromosomes (23 pairs).
Summary of the overall change and comment
Human body cells are diploid
because have two versions of each chromosome, one from the individual's
father and one from the individual's mother (23 pairs of chromosomes in
total).
On cell division, two identical
cells are formed in mitosis, and both nuclei will contain the same number of
chromosomes as the original cell (i.e. both cells are once again diploid).
Mitosis creates new cells for growth,
replacing damaged cells or tissue, and many organisms (both plant and
animal) use mitosis for asexual reproduction.
It should be noted that in asexual
reproduction, there is no genetic variation.
Mitosis is crucial to replacing damaged cells,
growth of new tissue and asexual reproduction.
Key points -
Summary of ideas
Based on
the syllabus-specifications for students taking the AQA, Edexcel and OCR
GCSE level biology examinations (~US grades 9-10).
Cell Division by Mitosis
– Revision Notes
Mitosis is a type of
cell division that produces two genetically identical
daughter cells from a single parent cell.
It is essential for growth, repair,
and asexual reproduction in multicellular organisms.
Stages of Mitosis
Mitosis consists of
four main stages: Prophase, Metaphase, Anaphase,
and Telophase (often remembered using the mnemonic PMAT).
1. Interphase
(Preparation Stage)
-
Not part of
mitosis, but essential
for cell division.
-
The cell grows and
carries out normal functions.
-
DNA
replication occurs,
doubling the genetic material.
-
Organelles and
proteins needed for mitosis are synthesized.
2. Prophase
-
Chromosomes
condense and become visible under a microscope.
-
Each chromosome
consists of two identical sister chromatids joined
at the centromere.
-
The nuclear
membrane breaks down.
-
Spindle fibres
begin to form from the centrioles (in animal
cells).
3. Metaphase
4. Anaphase
5. Telophase
-
Chromatids
decondense (becoming less visible).
-
New nuclear
membranes form around
each set of chromosomes.
-
The spindle
fibres break down.
6. Cytokinesis
(Final Division)
-
Cytoplasm divides,
creating two genetically identical daughter cells.
-
In animal
cells, the membrane pinches inwards.
-
In plant cells,
a cell plate forms between the two new cells.
Key Features of
Mitosis
Produces two
genetically identical daughter cells.
Maintains the same number of chromosomes as the parent
cell.
Essential for growth, repair, and
asexual
reproduction.
Occurs in somatic (body) cells, not gametes.
A rapid process with
no genetic variation.
Importance of
Mitosis
-
Growth:
Increases the number of cells for development.
-
Repair:
Replaces damaged or dead cells.
-
Asexual
Reproduction: Allows
organisms like bacteria, hydra, and plants to
reproduce without gametes.
-
Maintenance:
Ensures genetic consistency in tissues.
Mitosis versus
Meiosis
|
Feature |
Mitosis |
Meiosis |
|
Number of
divisions |
1 |
2 |
|
Number of daughter
cells |
2 |
4 |
|
Genetically
identical cells? |
Yes |
No |
|
Role in the body |
Growth, Repair,
Asexual Reproduction |
Gamete Production |
|
Occurs in? |
Somatic cells |
Gametes |
Summary of
learning objectives and key words or phrases
Be able to interpret and explain diagrams explaining
cell division by mitosis stages in the cell cycle.
Know what happens in the interphase, prophase,
metaphase, anaphase, telophase and the process of cytokinesis in asexual
reproduction to produce genetically identical cells.
WHAT NEXT?
TOP OF PAGE
Index for biology notes on
cell division
INDEX of all my BIOLOGY NOTES
HOME PAGE of Doc Brown's Science
website
UK KS3 Science Quizzes for
KS3 science students aged ~11-14, ~US grades 6, 7 and 8
Biology * Chemistry
* Physics UK
GCSE level students aged ~14-16, ~US grades 9-10
Advanced Level Chemistry
for pre-university age ~16-18 ~US grades 11-12, K12 Honors
Find your GCSE/IGCSE
science course for more help links to all science revision notes
email doc
brown - comments - query?
Doc Brown's school biology revision notes: GCSE biology, IGCSE
biology, O level biology, ~US biology science grade 8, grade 9 and
grade 10 school science courses or equivalent for ~14-16 year old students of
biology IGCSE AQA GCSE Biology Edexcel GCSE Biology IGCSE OCR Gateway Science
Biology OCR 21st Century Science Biology Some of these biology revision notes
might be suitable for UK KS3 Science-Biology courses for ages 12-14 (~US biology
science grades 6, grade 7 and
grade 8)
Explaining the importance of
stages of cell division by mitosis explained
in GCSE level biology, What you need to know about stages of cell
division by mitosis explained for
GCSE level
biology,
Explaining the use of stages of cell division by mitosis explained knowledge in GCSE level biology, Examples of
stages of cell division by mitosis explained when studying GCSE level biology, What is
the significance of stages of cell division by mitosis explained in GCSE level biology, describing and
explaining the theory of stages of cell division by mitosis explained when studying GCSE level biology, revision
notes for stages of cell division by mitosis explained in exams, online help for understanding
stages of cell division by mitosis explained, exam revision
notes for stages of cell division by mitosis explained, what do I need to learn about
stages of cell division by mitosis explained? revision summary for stages of
cell division by mitosis explained, learning notes for stages of cell division
by mitosis explained, help to pass the stages of cell division by mitosis
explained
topic in an exam question, how to prepare for questions on stages of
cell division by mitosis explained in a GCSE
biology examination?
Based on the syllabus-specifications
for students taking the IGCSE/GCSE level biology examinations summary
revision notes and key points on stages of cell division by mitosis
explained for students taking the AQA
igcse/gcse biology notes on stages of cell division by mitosis explained, Edexcel gcse
biology notes on stages of cell division by mitosis explained, OCR 21st century GCSE
biology notes on stages of cell division by mitosis explained, OCR gateway
GCSE biology notes on stages of cell division by mitosis explained, WJEC gcse biology notes on
stages of cell division by mitosis explained, CCEA
gcse biology notes on stages of cell division by mitosis explained for students taking CIE Cambridge igcse
biology, or any other GCSE or IGCSE level biology exams notes on
stages of cell division by mitosis explained, useful for US grade 9-10 biology courses
Website content © Dr
Phil Brown 2000+. All copyrights reserved on revision notes, images,
quizzes, worksheets etc. Copying of website material is NOT
permitted. Exam revision summaries and references to science course specifications
are unofficial. These notes are suitable for AQA gcse
biology,
Edexcel gcse biology, OCR gcse Gateway science biology, OCR 21st Century
science biology, WJEC GCSE biology, CCEA gcse biology, CIE Cambridge IGCSE
biology exams.
|
