Learning out comes

Define mitosis and state its importance in

growth , development and asexual

reproduction.

Define meiosis and state its importance in

the formation of gametes and in producing

genetic variation.

How did we change from a baby

to adult?

What caused those changes?

How do we generate new cells?

Here are the answers ................

The cell division

New cells are produced by the

division of the old ones.

Before the cell divide the nucleus must divide.

As the nucleus is finishing its division in to two the cytoplasm divides.

The cell division

In animal cell a construction occurs

between the two nuclei to divide the cell in to two.

The cell division

In plant cell a new cell wall is formed between the nuclei.

The cell division

There are two ways in which nuclei divide

Mitosis: Is a type of nuclear division that occurs during growth and asexual reproduction.

Meiosis: Occurs in sex organs to form gametes the daughter cells are genetically identical.

Mitosis

Mitosis is used when a cell needs to produce exact copies of itself.

Everything in the cell is duplicated.

The two new cells have the same DNA, functions, and genetic code.

The original cell is called the mother cell and the two new cells are called daughter cells.

As a result of mitosis each daughter cell has the same chromosomal number as the original parent cell.

Mitosis

1. Chromosomes make

identical copies of

themselves.

2. They line up along the

centre.

3. They move apart.

4. Two daughter cells

form with identical

chromosomes to the

parent cell.

Some cells continually

divide all through life.

These are stem cells

E.g. Cells of bone

marrow.

They continually

produce red blood

cells and phagocytes .

Stem cells

A stem cell is

essentially

the building block

of the human body.

A stem cell is

pluripotent - When it

divides, it can make any

one of the 220 different

cells in the human

body.

Stem cells

Mitosis occurs in the following process

Growth: In animals this happens all over the

body , in plants it happens in special growing

areas such as the tips of stems and roots.

Repair of wounds: Your skin cells divide by

mitosis to repair damaged tissue and wounds.

Replacement of cells: That wear out and die

such as red blood cells which only live for a

short period.

Asexual reproduction: This occurs in fungi,

protists and in plants but is rare in animal

kingdom.

Mitosis occurs in the following process

Meiosis

Meiosis is the type of cell

division by which gametes (eggs

or sperm) are formed.

If human sperm cell and egg cell both had 46 chromosomes the zygote formed at fertilization would have 92 chromosomes.

If this continued generation after generation the number of chromosomes in the nuclei would double every generation.

This does not happen. Instead the number remains 46 This is because there is a different sort of

nuclear division producing gametes this type of nuclear division is meiosis.

Meiosis

Meiosis halves the number of

chromosomes so egg and sperm cells

only have 23 chromosomes each.

Meiosis

The zygote has 46 chromosomes , 23 from the

mother in the egg and 23 from the father in the

sperm.

In sexual reproduction the number of

chromosomes stays constant from generation

to generation.

Meiosis

Where does Meiosis occur?

Meiosis occurs in sex organs in human - the ovaries

and testis.

In flowering plants meiosis occurs in

anthers and in the ovules.

Where does Meiosis occur?

How are the daughter cells in meiosis

In meiosis daughter cells are not identical.

They are genetically different and this contributes to genetic variation that provides the raw material for selection and allow organisms to evolve in response to changing environments.

Mitosis vs. Meiosis

Diploid cells

Clone

Same genetic information in parent cell and daughter cell.

Haploid cells Daughter cells

different from parent cell and from each other.

Daughter cells have

½ the number of chromosomes as somatic cell.

Key points

Mitosis produces daughter cells genetically

identical and have same number of

chromosomes as parent cell.

Meiosis is involved in gamete production in

sex organs. It produces a halving of

chromosome number in cells from the diploid

to the haploid number.

Meiosis results in genetic variations so, unlike

mitosis the cells are not genetically identical.