ks4 biology

© Boardworks Ltd 20041 of 29

KS4 Biology

Cell Division and Fertilization



Contents

Introducing cell division

What is mitosis?

What is meiosis?

Mitosis or meiosis?

Chromosomes and fertilization


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?


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.


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.

Knowing about chromosomes and what happens to them during cell division is the key to understanding the differences between mitosis and meiosis.



Contents


What is mitosis?

What is meiosis?

Mitosis or meiosis?



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.


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


What is mitosis?

What is meiosis?

Mitosis or meiosis?



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


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?


Fertilization animation

FLASH 6 – FertilisationFLASH 2 – Mitosis drag & drop


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


What is mitosis?

What is meiosis?

Mitosis or meiosis?



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

firstdivision

seconddivision

4 new cells

How many chromosomes do the new cells have compared to the original?


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.


Meiosis activity


Meiosis animation


Meiosis summary

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


Stages of meiosis activity



Contents


What is mitosis?

What is meiosis?

Mitosis or meiosis?



Mitosis or meiosis?


Who wants to have a million cells?

FLASH 2 – Mitosis drag & drop

ks4 biology

Documents