Transcript Cell Division and Fertilization - dp-mti

KS4 Biology
Cell Division
and Fertilization
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Contents
Cell Division and Fertilization
Introducing cell division
What is mitosis?
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How many cells?
An adult human is made up of about 100 trillion cells.
That’s 100 000 000 000 000 cells!
Everyone started out as just one single cell.
How does one cell become 100 trillion?
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By cell division – called…..
MITOSIS
This animation will be
explained in more detail
in the slides to come.
For now, just sit back
and watch it.
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Mitosis
Why is mitosis important?
For growth –
How else would you go
from being a single
fertilized egg cell to the
young person you are
today?
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To replace worn/ damaged cells –
- did you know that we shed our skin cells
about every 35 days. But don't worry, we do
not shed all our skin cells at the same time like
snakes do. In human beings, only the skin
cells that are old are shed, others are not.
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To repair damaged tissue
-when you cut yourself,
new skin cells will grow
to seal the wound.
These new cells come
from preexisting cells
found near the wound
that divided many, many
times.
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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.
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What is mitosis?
Mitosis begins with a single cell.
How many chromosomes does
this cell contain?
(answer: 4)
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
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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!
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Stages of Mitosis
At the end of Interphase, a cell that is ready
to divide looks like this:
Loosely
coiled DNA
The cell has grown to nearly 2X its original size, and the
DNA has been copied.
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The actual process of dividing is
called : Mitosis
There are 4 main stages:
Prophase
Metaphase
Anaphase
Telophase
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Prophase
Prophase
- nuclear membrane starts to break
down
- The loosely coiled DNA
condenses (gets supercoiled)forms chromosomes. You can
see chromosomes (like the letter
“X”) in a microscope
- Centrioles release spindle fibres;
spindle fibers will attach to the
centromere of each chromosome
- by the end of prophase, the
nuclear membrane is completely
gone
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Metaphase
• The chromosomes move
to the middle of the cell
• spindle fibers, attached to
the centromere of each
chromosome, help the
chromosomes move to
the middle
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Anaphase
• Each chromosome
separates so that a
copy of each DNA
molecule moves to
the poles of the cell
• Spindle fibers pull the
separated
chromosomes to the
poles (ends) of the
cell
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Telophase
• The spindle fibers disappear
• A nuclear membrane reforms
around each set of chromosomes
• The chromosomes begin to uncoil
(from supercoiled to loosely coiled)
• The cell begins to pinch apart at
the centre until it completely
separates into 2 distinct cells, each
with its own set of genetic material
(DNA). This division of the
cytoplasm is called cytokinesis.
Cell organelles are also equally
distributed between the daughter
cells
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On the next slide is an animation of mitosis.
In your kit is a step by step narrative of what
you will see. Read the script as you play the
animation. Repeat the process in order to
get a better understanding.
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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
Wwha
Wwhh
Whad
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