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KS4 Biology. Cell Division and Fertilization. Contents. Cell Division and Fertilization. Introducing cell division. What is mitosis?. Chromosomes and fertilization. What is meiosis?. Mitosis or meiosis?. How many cells?. An adult human is made up of about 50 billion cells.

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ks4 biology

KS4 Biology

Cell Division

and Fertilization

contents
Contents

Cell Division and Fertilization

Introducing cell division

What is mitosis?

Chromosomes and fertilization

What is meiosis?

Mitosis or meiosis?

how many cells
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
Cell division

New cells are produced by old cells dividing.

Why are new cells needed?

  • 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…

…mitosis and meiosis.

cell division and genetic information
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?

cell division and chromosomes
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.

contents1
Contents

Cell Division and Fertilization

Introducing celldivision

What is mitosis?

Chromosomes and fertilization

What is meiosis?

Mitosis or meiosis?

what is mitosis

Mitosis begins with a single cell. How many chromosomes does this cell contain?

First the cell makes a copy

of each chromosome…

What is mitosis?

original cell

…then it divides.

cell division

Each new cell has a full set of chromosomes and is identical to the original cell.

2 new cells

what is mitosis1
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 summary
Mitosis summary

How does mitosis turn one cell into two new cells?

contents2
Contents

Cell Division and Fertilization

Introducing celldivision

What is mitosis?

Chromosomes and fertilization

What is meiosis?

Mitosis or meiosis?

how many chromosomes

How many chromosomes are there in each new human body cell produced by mitosis?

How many chromosomes are there in human sex cells?

How many chromosomes?

46 chromosomes

(23 matching pairs)

23 unpaired chromosomes

23 unpaired chromosomes

how many chromosomes1
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
Fertilization animation

FLASH 6 – Fertilisation

FLASH 2 – Mitosis drag & drop

sex cells and cell division
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?

contents3
Contents

Cell Division and Fertilization

Introducing cell division

What is mitosis?

Chromosomes and fertilization

What is meiosis?

Mitosis or meiosis?

what is meiosis
What is meiosis?

Meiosis begins with a single cell.

original cell

First the cell makes a copy

of each chromosome.

first

division

Now, there are two stages of cell division…

second

division

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

4 new cells

what is meiosis1
What is meiosis?

Meiosis produces four new sex cells with half the original number of chromosomes.

In animals, meiosis produces ova in females and sperm cells in males.

In plants, the gametes produced by meiosis are pollen grains and ovules.

Mitosis is also called reduction division.

What does this mean?

meiosis summary
Meiosis summary

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

contents4
Contents

Cell Division and Fertilization

Introducing cell division

What is mitosis?

Chromosomes and fertilization

What is meiosis?

Mitosis or meiosis?

who wants to have a million cells
Who wants to have a million cells?

FLASH 2 – Mitosis drag & drop