Cell Division
Chapter 14
Intro worksheet
Why do cells divide in organisms?
What are chromosomes?
Where are chromosomes found?
In pairs discuss
1. Why do cells divide in
organisms?
2. What are chromosomes?
3. Where are chromosomes
found?
Aidhm
Explain the terms: cell continuity &
chromosomes.
2. Define the terms: haploid number &
diploid number.
3. Describe the cell cycle in the state
of non-division (Interphase) and
division (mitosis).
1.
Cell Cycle – flow chart
4
Cell Continuity
Cell continuity: All cells
develop from pre-existing cells
It involves growth, synthesis and
reproduction.
Chromosome Structure
6
Chromosomes
contain genes
 composed of DNA and proteins
 Chromosomes occur in pairs in most plant
and animal cell nucleii.

A gene is a short section of DNA.
 It is the unit of inheritance.
 It controls the development of a particular
characteristic
 A gene has a particular locus (position) on a
chromosome

7
Chromosomes

When not dividing = Chromatin (long thin
threads)

When dividing = Chromatin forms a numbers of
clearly distinguishable Chromosomes

Each species has a definite no. of Chromosomes,
Humans= 46 chromosomes

Each Chromosomes has 1000s of genes
How many chromosomes?
Each species has a characteristic number of
chromosomes.
 Humans have 46
 23 from their mother
 23 from the father
 A human has 23 pairs
 You have two of each type of chromosome.

12
Haploid
A Haploid cell has one set of chromosomes

has only one set of each type of chromosomes in
the nucleus.

Haploid is symbolised by letter ‘n’ and number of
chromosomes in the cell is n=23

In humans, eggs and sperm are haploid n=23
Diploid
A Diploid has pairs of chromosomes

It has two of each type of chromosome in the
nucleus

These pairs of chromosomes in diploid cell are
called homologous pairs.

Diploid is symbolised as ‘2n’ and total no. of
chromosomes in cell is 2n=46
• In diploid cells,
1 chromosome
from the
homologous
pair comes from
the mother and
the other comes
from the father.
Cell Cycle
Describes the life of a cell.
 Interphase = when cell is not dividing
 Mitosis = when cell divides

Interphase
Mitosis or
Meiosis
Interphase
When cells are not dividing
 Longest phase in cell cycle
 Chromosomes elongated =
chromatin
What occurs during interphase
 New mitochondria
 Chloroplasts are produced
 Duplication of chromosomes occurs

Learning Check
1.
2.
3.
What 2 stages are involved in cell
continuity, which is longest? What is
meant by haploid and diploid?
What is a chromosome, what is it made
up of, what is it known as when not
dividing ?
How many chromosomes are found in a
typical human cell, how many found in a
gamete, what are the chromosomes for
a male and a female?
Can you…..
Explain the terms: cell continuity &
chromosomes.
2. Define the terms: haploid number &
diploid number.
3. Describe the cell cycle in the state
of non-division (Interphase) and
division (mitosis).
1.
5-5-1 Deluxe!
Back to
Plenaries
Now reduce that to 5 key words…
Write 5 sentences summarising today’s
topic…
And finally to one word….
Use shapes and pictures to
deluxe-ify 5-5-1
Aidhm
1.
2.
3.
Define the term: mitosis.
Explain the process of mitosis in simple
terms, with the aid of diagrams to show
chromosome behaviour.
State the primary function of mitosis for
single-celled and multicellular organisms.
https://www.youtube.com/watch?fea
ture=player_embedded&v=VlN7K19QB0
Mitosis

Mitosis is a form of nuclear division in which
one nucleus divides to form two nuclei.
Each nucleus contains identical sets of
chromosomes.

Two new cells called daughter cells and they are
IDENTICAL to each other.
Mitosis
A sentence to help you remember the 4
stages of mitosis
I
 Interphase
 Party
 Prophase
 Monday
 Metaphase
 And
 Anaphase
 Tuesday  Telophase
THE CELL CYCLE
Stages of Mitosis
Stages of Mitosis
Prophase
• Spindle fibres begin to appear
• Chromosomes contract and duplicate. The point
where the strands are held together is called a
centromere
HL
• The nucleolus (part of nucleus where ribosomes are
made) breaks down
• Nuclear membrane starts to break down
Stages of Mitosis
Metaphase
• Nuclear membrane breaks down completely
• Chromosomes contract even more
• Chromosomes line up across the equator of the
cell
• Spindle fibres attach to the centromere of each
chromosome. One fibre attaches from each end to
every chromosome.
Stages of Mitosis
Anaphase
• Spindle fibres contract
• Centromere splits
• One strand from each chromosome is pulled to
either end of the cell.
• The chromosomes at each end of the cell have
identical set of genes
• Shortest phase
Stages of Mitosis: Telophase
OL
HL
• Spindle fibres break down
• Chromosomes elongate to from chromatin
• When mitosis is complete, the cell divides into 2 cells
which are identical.
HL
• One or more nucleolus begin to reform
• Nuclear membrane forms around each of the 2 sets of
chromatin
Functions of Mitosis
Unicellular Organisms
 Reproduction for Amoeba (Asexual reproduction).
In Multicellular Organisms
 Produces new cells, not new individuals
 Responsible for growth
 Responsible for renewal and repair of cells
 Found in root and shoot tips of plants, buds
Root tip of onion
Can you….
1.
2.
3.
Define the term: mitosis.
Explain the process of mitosis in simple
terms, with the aid of diagrams to show
chromosome behaviour.
State the primary function of mitosis for
single-celled and multicellular organisms.
Aidhm
Explain cell division in plants and
animals in more detail
2. Define cancer and state two possible
causes.
3. Define the term: meiosis.
4. State the functions of meiosis.
1.
Cell Division
HL
1. Animal Cells
• Cell division occurs by cleavage
• A cleavage furrow appears along the
equator of the cell
• It deepens and splits the cytoplasm
2. Plant Cells
• Cell wall prevents cleavage
furrow forming
• Vesicles containing
cellulose gather in the area
between the 2 nuclei
• The vesicles form a cell
plate
• The membrane of the cell
plate joins the plasma
membrane of the original
cell
• 2 cell walls form
• Middle lamella = region
between the 2 cell walls
www.edcodigital.ie
Animations of stages on chapter 14
Cancer

A cell or group of cells
lose the ability to control
the rate of mitosis or cell
division.

They form a mass of cells
called a tumour which can be
benign or malignant.
Cancer
Benign tumours
 Benign means kind, not life threatening and do not
invade other tissues. Eg warts, skin tags.
 Cells stop dividing after some time
Malignant tumours
 Uncontrolled multiplication of abnormal cells
 Malignant tumours (cancers) invade other cells
and move around the body
 Movement of these cells called Metastasis.
 Cancer cells divide indefinitely.
Causes of Cancer
Oncogenes: When normal genes are altered
to form cancer-causing genes
1. Carcinogens (cancer causing): cigarette
smoke, asbestos fibres, uv
2.
Some viruses
Learning Check
1.
2.
3.
4.
5.
6.
What is the function of mitosis in multicellular
organisms?
What is the function of mitosis in unicellular
organisms?
How do tumours form?
What is the difference between benign and
malignant tumours?
When cancer cells spread it is called
m......................?
Can you name 3 possible causes of cancer?
Meiosis
Meiosis

A form of nuclear division in which the
daughter nuclei contain half the number of
chromosomes of the parent nucleus.

Human cells have 46 chromosomes
Meiosis occurs in the ovaries and testes to
produce gametes called eggs and sperm so
there are 23 chromosomes in each egg and
sperm
 Meiosis in a diploid (2n) cell produces 4 haploid
(n)cells

Functions of Meiosis
2 functions in Multicellular Organisms
 Allows sexual reproduction without increasing
the number of chromosomes in the offspring
 Allows new combinations of genes
Meiosis
Products of Mitosis
& Meiosis compared
Mitosis
Meiosis
56
Mitosis
Vs
Meiosis
(1/2)
Resulting nuclei not
identical – variation
 Daughter cells have half
the no. of chromosomes
as parent.

Resulting nuclei identical

No reduction in
chromsomes

One cell divides to form 2  One cell divides to form 4

57
4.
9 +8 +3(1)
Example: The cells produced by meiosis are haploid
T
The cells produced by mitosis are identical
T
Meiosis gives rise to variation
T
Mitosis always produces four new cells
F
Meiosis is never involved in gamete formation
F
Single-celled organisms use mitosis for reproduction
T
Can you….
Explain cell division in plants and
animals in more detail
2. Define cancer and state two possible
causes.
3. Define the term: meiosis.
4. State the functions of meiosis.
1.
WWTBM 1
END
As easy as 1 2 3
Most human cells have 46 chromosomes
There are 4 stages of mitosis
Interphase is the longest part of a cell cycle