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KS4 Biology

Cell Division and Fertilization


Cell Division and Fertilization

Contents

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!

Everyone started out as just one single cell.How does one cell become 100 trillion?


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.


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?


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.


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.


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 informationcarried 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.


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?(answer: 4)

First the cell makes a copy of each chromosome…

original cell

cell division

2 new cells

…then it divides.


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!


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.


The actual process of dividing is called : Mitosis

There are 4 main stages:

ProphaseMetaphaseAnaphaseTelophase


ProphaseProphase - 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


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


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


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


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.


Mitosis animation


Mitosis summary

How does mitosis turn one cell into two new cells?


Stages of mitosis activity

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