KS 4 Biology Cell Division and Fertilisation Boardworks

KS 4 Biology • Cell Division • and Fertilisation © Boardworks Ltd 2004

Contents Cell Division and Fertilisation Introducing cell division What is mitosis? Chromosomes and fertilisation What is meiosis? Mitosis or meiosis? © Boardworks Ltd 2004

How many cells? An adult human is made up of about 50 billion cells. That’s 50 000 000 cells! Everyone started out as just one single cell. How does one cell become 50 billion? © Boardworks Ltd 2004

Cell division New cells are produced by old cells dividing. Why are new cells needed? l Growth and repair of body cells. l 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. © Boardworks Ltd 2004

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 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? © Boardworks Ltd 2004

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. © Boardworks Ltd 2004

Contents Cell Division and Fertilisation Introducing cell division What is mitosis? Chromosomes and fertilisation What is meiosis? Mitosis or meiosis? © Boardworks Ltd 2004

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 © Boardworks Ltd 2004

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? © Boardworks Ltd 2004

Mitosis animation © Boardworks Ltd 2004

Mitosis summary How does mitosis turn one cell into two new cells? © Boardworks Ltd 2004

Stages of mitosis activity © Boardworks Ltd 2004

Contents Cell Division and Fertilisation Introducing cell division What is mitosis? Chromosomes and fertilisation What is meiosis? Mitosis or meiosis? © Boardworks Ltd 2004

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 © Boardworks Ltd 2004

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. l They have half the usual number of chromosomes. l They have a complete set of single chromosomes. Why is this important for fertilisation and reproduction? © Boardworks Ltd 2004

Chromosomes and fertilisation FLASH 6 – Fertilisation FLASH 2 – Mitosis drag & drop © Boardworks Ltd 2004

Chromosomes and fertilisation © Boardworks Ltd 2004

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? © Boardworks Ltd 2004

Contents Cell Division and Fertilisation Introducing cell division What is mitosis? Chromosomes and fertilisation What is meiosis? Mitosis or meiosis? © Boardworks Ltd 2004

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 © Boardworks Ltd 2004

What is meiosis? Meiosis produces four new sex cells with half the original number of chromosomes. In animals, meiosis produces eggs in females and sperm cells in males. In plants the gametes produced by meiosis are pollen grains and ovules. © Boardworks Ltd 2004

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

Stages of meiosis activity © Boardworks Ltd 2004

Contents Cell Division and Fertilisation Introducing cell division What is mitosis? Chromosomes and fertilisation What is meiosis? Mitosis or meiosis? © Boardworks Ltd 2004