Presentation on theme: "Cells & Mitosis This is a typical plant cell. Chloroplasts contain the green chemical chlorophyll which is used in photosynthesis."— Presentation transcript:
Cells & Mitosis
This is a typical plant cell.
Chloroplasts contain the green chemical chlorophyll which is used in photosynthesis.
The cell wall is a strong rigid boundary around plant cells. It is made of cellulose, and assists in the support of plants.
This is a typical animal cell.
The plasma membrane is a flexible skin like material which surrounds the cell and holds its contents together. It allows some chemicals through and keeps out others.
The cytoplasm is the fluid material in cells. It is mainly water, but has gases and other chemicals dissolved in it.
The mitochondria are small organelles found in all cells which are responsible for energy production.
The nucleus is the ‘control centre’ of the cell. It determines how the cell functions. It contains all the genetic information.
(ie chromosomes, genes, DNA)
When a cell grows large enough it will reproduce by splitting into two new cells.
Each of these new (daughter) cells must contain the same number of chromosomes as the original cell.
The process that enables this to occur is called mitosis. Mitosis is occurring in your body right now. It has been since you were just a fertilized egg. It is how you have gone from just this one cell to the billions of cells that you are now.
The human sperm has 23 chromosomes. The human egg (ova) has 23 chromosomes. When the egg is fertilised these chromosomes pair up. The fertilised egg therefore has 23 pairs of chromosomes. Every human cell (apart from the sperm and ova) have 23 pairs of chromosomes.
If when the fertilised egg underwent its first division, it merely split its contents there’d be only 23 chromosomes in each daughter cell.
Next division there’d be 11 ½ chromosomes in each cell!!! These cells would no longer be human.
Mitosis allows the cells to maintain the correct number of chromosomes with each division.
During the early stage of mitosis the chromosomes thicken and copy themselves. This is called replication.
This process of replication results in two identical sister chromatids.
Cells in an onion root.
When the cell divides the sister chromatids divide and go to each daughter cell.