Transcript KS4 Cell Division and Fertilization

Contents
Cell Division and Fertilization
Introducing cell division
What is mitosis?
Chromosomes and fertilization
What is meiosis?
Mitosis or meiosis?
1 of 35
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 billion?
Cell division
New cells are produced by old cells dividing.
Why are new cells needed?
 Growth and repair
of body cells.
 Production of
specialised sex cells.
New cells are needed for two main reasons, so there are
two different types of cell division…
…mitosis and meiosis.
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?
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.
Contents
Cell Division and Fertilization
Introducing cell division
What is mitosis?
Chromosomes and fertilization
What is meiosis?
Mitosis or meiosis?
What is mitosis?
Mitosis begins with a single cell.
How many chromosomes does
this cell contain?
original
cell
First the cell makes a copy
of each chromosome…
…then it divides.
cell
division
Each new cell has a full set
of chromosomes and is
identical to the original cell.
2 new cells
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?
Mitosis activity
Mitosis animation
Mitosis summary
How does mitosis turn one cell into two new cells?
Stages of mitosis activity
Contents
Cell Division and Fertilization
Introducing cell division
What is mitosis?
Chromosomes and fertilization
What is meiosis?
Mitosis or meiosis?
How many chromosomes?
How many chromosomes are there
in new human body cells produced
by mitosis?
46 chromosomes
(23 matching pairs)
How many chromosomes are there in human sex cells?
23 unpaired chromosomes
23 unpaired chromosomes
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?
Chromosomes and fertilization
FLASH 6 – Fertilisation
FLASH 2 – Mitosis drag & drop
Chromosomes and fertilization
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?
Contents
Cell Division and Fertilization
Introducing cell division
What is mitosis?
Chromosomes and fertilization
What is meiosis?
Mitosis or meiosis?
What is meiosis?
Meiosis begins with a single cell.
original
cell
First the cell makes a copy
of each chromosome.
Now, there are two stages
of cell division…
How many chromosomes
do the new cells have
compared to the original?
first
division
second
division
4 new cells
What is meiosis?
Meiosis produces four new
sex cells with half the original
number of chromosomes.
In animals, meiosis
produces ova in females
and sperm cells in males.
In plants the gametes
produced by meiosis are
pollen grains and ovules.
Mitosis is also called
reduction division.
What does this mean?
Meiosis activity
Meiosis animation
Meiosis summary
How does meiosis turn one cell into four new sex cells?
Stages of meiosis activity
Contents
Cell Division and Fertilization
Introducing cell division
What is mitosis?
Chromosomes and fertilization
What is meiosis?
Mitosis or meiosis?
Mitosis or meiosis?
Who wants to have a million cells?
FLASH 2 – Mitosis drag & drop