Topic 2.5Cell division

2.5.1 Cell Cycle

2.5.2 Uncontrolled cell division: tumour cellsThe cell division cycle is regulated in a number of ways.

Certain agents can damage these regulatory elements.

When this happen, uncontrolled cell division can occur resulting in the formation of tumours.

2.5.2 Uncontrolled cell division: tumours cells

S OF INTERPHASE G2 OF INTERPHASE MITOTIC PHASE

2.5.3 Interphase

2.5.4 The phases of Mitosis: Prophase

MTOC (pair centrioles)

1. Chromosomes supercoil and become visible

2. The spindle of microtubules forms from the

MTOC (microtubule organizing centre)

1. In animal cell, the centrioles divide and

move to opposite ends (poles) of the

nucleus.

2. In plant cells, there are no centrioles and

the spindle microtubules forms

independently.

3. Each chromosome consists of two chromatids

held together by the centromere.

4. Nuclear envelop breaks down.

1. Spindle microtubules attaches to the

chromosomes by means of the centromere.

2. Chromosomes are moved to the equator of

the cell,

2.5.4 The phases of Mitosis: Metaphase

The pair of sister chromatids separate and the

spindle microtubules pull them towards opposite

poles of the cell.

2.5.4 The phases of Mitosis: Anaphase

1. The chromatids have now reached the poles

and can be regarded as distinct chromosomes.

2. The nuclear envelop forms around each group

of chromosomes.

3. Chromosomes uncoil

4. The cytoplasm divide by a process called

Cytokinesis.

2.5.4 The phases of Mitosis: Telophase

Cytokinesis: Cytoplasm division

2.5.5 Explain how mitosis produce two genetically identical nuclei

Reproduction. An ameba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism

Growth & Development. A sand dollar embryo shortly after the fertilized egg divided forming two cells.

Tissue renewal. This dividing bone marrow cells (arrow) will give rise to new blood cells.

2.5.6 Why do cells divide?

1. Asexual Reproduction

2. Growth & Embryonic Development

3. Tissue Renewal