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© Boardworks Ltd 2004 1 of 29 KS4 Biology Cell Division and Fertilization

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KS4 Biology. Cell Division and Fertilization. Contents. Cell Division and Fertilization. Introducing cell division. What is mitosis?. How many cells?. An adult human is made up of about 100 trillion cells. That’s 100 000 000 000 000 cells!. - PowerPoint PPT Presentation


Cell Division and FertilizationHow 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?
This animation will be explained in more detail in the slides to come. For now, just sit back and watch it.
© Boardworks Ltd 2004
For growth –
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.
© Boardworks Ltd 2004
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.
© Boardworks Ltd 2004
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?
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.
What is mitosis?
Each new cell has a full set of chromosomes and is identical to the original cell.
original cell
cell division
2 new cells
…then it divides.
Mitosis begins with a single cell. How many chromosomes does this cell contain?
(answer: 4)
of each chromosome…
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!
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.
© Boardworks Ltd 2004
There are 4 main stages:
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
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
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.
1. D, 2. F, 3. A, 4. G,
5. E, 6. C, 7. B, 8. H.