1) The document discusses the two types of cell division: mitosis and meiosis. Mitosis produces new body cells for growth and repair through copying of chromosomes, while meiosis produces gametes like sperm and egg cells through reducing chromosome number. 2) Meiosis takes place in the gonads/sex organs and results in four gamete cells each with half the number of chromosomes as the original cell. 3) Fertilization occurs when gametes from each parent fuse, restoring the full chromosome number and allowing for reproduction.

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KS4 Biology
Cell Division
and Fertilization

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Cell Division and Fertilization
Contents
Introducing cell division
What is mitosis?
What is meiosis?
Mitosis or meiosis?
Chromosomes and fertilization

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How many cells?
An adult human is made up of about 50 billion cells.
That’s 50 000 000 000 000 cells!
Everyone started out as just one single cell.
How does one cell become 50 million million?

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Cell division
 Growth and repair
of body cells.
 Production of
specialized sex cells.
New cells are needed for two main reasons, so there are
two different types of cell division…
New cells are produced by old cells dividing.
Why are new cells needed?
…mitosis and meiosis.

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Cell division and genetic information
Cells don’t just split in half when they
divide. If they did, there wouldn’t
be much of the cells left!
It is essential that the genetic
information carried in a cell
is transferred to the new cells.
Where is genetic information
carried in a cell?
When a cell divides how can this genetic information
be transferred without any of it being lost?

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Cell division and chromosomes
Chromosomes in the nucleus carry
the genetic information of a cell.
Chromosomes must be accurately
copied and passed on during
cell division.
This is important to make sure
that no genetic information is lost.
Knowing about chromosomes and what happens to them
during cell division is the key to understanding the
differences between mitosis and meiosis.

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Cell Division and Fertilization
Contents
Introducing cell division
What is mitosis?
What is meiosis?
Mitosis or meiosis?
Chromosomes and fertilization

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What is mitosis?
Each new cell has a full set
of chromosomes and is
identical to the original cell.
Mitosis begins with a single cell.
How many chromosomes does
this cell contain?
First the cell makes a copy
of each chromosome…
original
cell
cell
division
2 new cells
…then it divides.

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What is mitosis?
Each new cell can keep on
dividing by mitosis.
Mitosis makes new cells for
growth and repair in all living
things. That’s how you get
from one cell to 50 billion!
Mitosis is also called
copying division.
What does this mean?

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Mitosis activity

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Mitosis animation

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Mitosis summary
How does mitosis turn one cell into two new cells?

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Stages of mitosis activity

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Cell Division and Fertilization
Contents
Introducing cell division
What is mitosis?
What is meiosis?
Mitosis or meiosis?
Chromosomes and fertilization

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How many chromosomes?
How many chromosomes are there in human sex cells?
How many chromosomes are there
in each new human body cell
produced by mitosis?
46 chromosomes
(23 matching pairs)
23 unpaired chromosomes
23 unpaired chromosomes

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How many chromosomes?
Human sex cells have a set of 23 unpaired chromosomes
– that’s half the usual number.
Sex cells in animals and plants follow the same rules.
 They have half the usual number of chromosomes.
 They have a complete set of single chromosomes.
Why is this important for fertilization and reproduction?

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Fertilization animation
FLASH 6 – Fertilisation
FLASH 2 – Mitosis drag & drop

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Chromosomes and fertilization

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Sex cells and cell division
Sex cells have half the usual number of chromosomes.
Why aren’t new sex cells produced by mitosis?
Sex cells have to be produced by a special type of cell
division. This is why there are two types of cell division.
Sex cells are produced by meiosis.
In which organs does meiosis take place?

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Cell Division and Fertilization
Contents
Introducing cell division
What is mitosis?
What is meiosis?
Mitosis or meiosis?
Chromosomes and fertilization

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What is meiosis?
Meiosis begins with a single cell.
First the cell makes a copy
of each chromosome.
Now, there are two stages
of cell division…
original
cell
first
division
second
division
4 new cells
How many chromosomes
do the new cells have
compared to the original?

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What is meiosis?
Meiosis produces four new
sex cells with half the original
number of chromosomes.
Mitosis is also called
reduction division.
What does this mean?
In animals, meiosis
produces ova in females
and sperm cells in males.
In plants, the gametes
produced by meiosis are
pollen grains and ovules.

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Meiosis activity

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Meiosis animation

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Meiosis summary
How does meiosis turn one cell into four new sex cells?

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Stages of meiosis activity

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Cell Division and Fertilization
Contents
Introducing cell division
What is mitosis?
What is meiosis?
Mitosis or meiosis?
Chromosomes and fertilization

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Mitosis or meiosis?

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Who wants to have a million cells?
FLASH 2 – Mitosis drag & drop