Biology AS F211 (Cell division)

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Cell cycles


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Stages of the cell cycle

Okay, the cell cycle consits of 4 stages G1, G2, M and S. They go in this order...

- G1 (Growth) In this stage the cell mainly grows, creating new proteins and more organelles.

- S (Synthesis) in this stage the DNA is replicates.

- G2 (more growth) in this stage more growth occurs.

(These first 3 stages occur in the interphase...)

- M (Mitosis) This is the stage where mitosis occurs.

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Stages of Mitosis

- Interphase this is the stage where DNA is replicated and checked.

- Prophase now the replicated chromosomes supercoil (thicken and shorten).

- Metaphase next the chromosomes line up down the middle of the cell.

Anaphase Spindles come from the centriole and attach to the cells centromere.

- Telophase The nuclei reform and two identical nuclei are produced.

The process of two cells splitting is called Cytokinesis.

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Uses of Mitosis

There are many uses of mitosis here are some of the main ones...

- Asexual reproduction

- Growth

- Repair - If you cut or hurt yourself..

- Replacement - Blood and skin cells need to be replaced continously.

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Homologous chromosomes

A homologous pair of chromosones, is a pair of chromosones which consist of two parent chromosomes which pair up, this happens in meiosis.

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Budding in Yeast

Cytokinesis (where the two cells seperate), is different inbetween plants and animals, but in yeast it is even weirder.

In yeast the cell produces a bud which nips off the other cell causing them to seperate.

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Stem cell

Stem cell - A stem cell is a cell which is undifferentiated, and it can become a number of different specialised cells.

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Differentiation and Specialisation

When a cell becomes specialised to a certain job, for example going from being a stem cell in the bone marrow to being a erythrocyte (red blood cell) we call this differentiation, becuase it has become specialised.

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Tissues, organs, and organ systems

Tissue - A group of cells that perform a particular.

Organ - A group of tissues working together to perform a function.

Organ system - A group of organs.

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Specialised Cells (Blood)


- No nucleus

- Lots of Haemoglobin

- Biconcave discs


- Packed full of lysosomes appears granular, these allow it digest invading organisms and pathogens.

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Specialised Cells (Sperm cells)

Sperm cells

- Filled with Mitochondria to provide energy for movement

- The sperm head contains Lysosomes to dissolve the surface of the egg.

- the long flagellum helps movement.

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