Biology AS F211 (Cell division)

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.

- 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.

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.

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

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.

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

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.

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.

Erythrocytes

- No nucleus

- Lots of Haemoglobin

- Biconcave discs

Neutrophils

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

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.