Cell cycle and Mitosis

The cell cycle is the process that all body cells use to grow and divide. The cell cycle starts when a cell is produced by cell division and ends with the cell dividing to produce two identical cells.

Interphase (cell-growth) is sub-divided into three seperate growth stages:

• Gap phase 1- cell grows and new proteins/organelles are made

• Synthesis- cell replicates its DNA, ready to divide by mitosis

• Gap phase 2- cells keep growing + proteins needed for cell division are made

Mitosis (cell division)- The cell cycle starts and ends here

Mitosis is needed for the growth of Multicellular Organisms (Humans) + for repairing damaged tissues.

Some organisms reproduce asexually (Plants, Fungi) using Mitosis. This means new organisms are genetically identical to the parent organism.

(Before Mitosis) is Interphase

- The cells DNA is unravelled + replicated, to double its genetic content. Organelles are also replicated so it has spare ones, ATP is increased. (energy needed for cell division)

Mitosis has 4 division stages:

• Prophase- Chromosomes condense getting shorter/fatter. Centrioles start moving to opposite ends of cell, forming a sprindle (a network of protein fibres). The nuclear envelope breaks down + chromosomes lie free in cytoplasm
  

• Metaphase- The chromosomes (each with 2 chromatids) line up along the middle of the cell and attach to the spindle by their centromere

• Anaphase- The centromeres divide, seperating the sister chromatids. The spindles contract, pulling chromatids to opposite ends of the cell, centromere first

• Telophase- Chromatids reach opposite ends of the sprindle. Chromatids uncoil + become long/thin again. They're now called chromosomes. A nuclear envelope forms around each group of chromosomes (two nuclei). The cytoplasm divides + there are now two daughter cells that are genetically identical to the original cell.
  
  

  Mitosis is finished + each daughter cell starts Interphase

1) Cut the tip from a growing root (Garlic). At about 5mm long

2) Place the sample in a shallow bowl + add a few drops of hydrochloric acid

3) Add a few drops of stain so that chromosomes become darker + easier to see under a microscope

4) Warm the bowl, but do not boil, by passing it through a bunson burner

5) Place the root tip on a microscopic slide + use a mounted needle to break it open + spread the cells out thinly

6) Add a few more drops of stain + place a cover slip over it

7) Squash the cover slip and warm it up for a few more seconds, to intensify the stain