Cell Division

Topic 1.6

Essential idea: Cell division is essential but must be controlled.

Understandings

1.6.U1 Mitosis is the division of the nucleus into two genetically identical daughter nuclei

1.6.U2 Chromosomes condense by supercoiling during mitosis

Mitosis involves four stages, including prophase, metaphase, anaphase and telophase. Textbooks vary in the use of the terms chromosome and chromatid but in these webpages the two DNA molecules formed by DNA replication are considered to be sister chromatids until the splitting of the centromere at the start of anaphase. Once the centromere splits they are individual chromosomes. Growth, embryonic development, tissue repair, and asexual reproduction involve mitosis. After mitosis the cell cytoplasm splits by a process known as cytokinesis to produce two cells.

Cell Division link Cell Division animation
Cell membrane stability

Terminology you need to know!

Difference between sister chromatids and chromosomes

1.6.U3 Cytokinesis occurs after mitosis and is different in plant and animal cells

Difference between animal and plants during cytokinesis

1.6.U4 Interphase is a very active phase of the cell cycle with many processes occurring in the nucleus and cytoplasm

The figure below illustrates the three stages of the cell cycle which occur in the order of interphase, mitosis and cytokinesis. Interphase is an active period in the life of a cell when many metabolic actions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts. Tumours (cancers) are the result of uncontrolled cell divisions where the cells continue through the cell cycle and can occur in any organ or tissue.

Stages in the cell cycle

1.6.U5 Cyclins are involved in the control of the cell cycle

Role of cyclins in the cell cycle

1.6.U5 Mutagens, oncogenes and metastasis are involved in the development of primary and secondary tumours

Formation of tumours

Applications

1.6.A1 The correlation between smoking and incidence of cancers

What do the graphs indicate regarding the correlation between smoking and lung cancer?

Click on Show explanation of importance to view correlation

Graph of smoking and lung cancer
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Correlation between smoking and cancer explained

Skills

1.6.S1 Identification of phases of mitosis in cells viewed with a microscope or in a micrograph

Can you identify the phase of mitosis shown in each micrograph below?
Placing your mouse pointer on each micrograph will reveal the phase of mitosis.

Anaphase micrograph
Prophase micrograph
Telophase micrograph
Metaphase micrograph

1.6.S2 Determination of a mitotic index from a micrograph

Mitotic index calculation

Practice: Mitotic index calculation

Calculate the mitotic index for the micrograph below.
Placing your mouse pointer on micrograph to see the mitotic index calculation.

Practic calculation of mitotic index
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