Cell Division and Growth• Why do the cells need to divide?• There are two main reasons for the cells to divide

1. Cell volume to surface area ratio: Cells cytoplasm and cell organelles grow at much fastre rate than the cell surface. That necessitates a cell division so that extra volume can be divided into two smaller units.

2. The nuclear and cell ratio : As the cell increases in size its nucleus remains the same size. A point comes when cell is too large to be controlled by the nucleus. So the cell divided into two so that the original nucleus to cytoplasm ratio can be maintained and the nucleus can effectively controll cellular processes.

Besides, cells are needed for;growth and development of the body from a single cell to a full bodyrepair the worn out cells in the body and replace the dead cells

Mitosis

• Mitosis is used to;

• Increase the number of cells in non reproductive cells called somatic cell

• Results in two daughter cells from one mother cell

• The daughter cells have exactly the same number of chromosomes as the mother cell

• The daughter cells have identical gene make up as the mother cells

• No variations are produced

• Necessary for asexual reproduction when the progenies are desired to be the same as parents

• Meiosis is used to;

• Produce cells in reproductive parts called gonadic or gametic cells

• Results in four daughter cells from one mother cell.

• The daughter cells have half the number of chromosomes than the mother cell

• All four daughter cells have different gene make up and are also different from the mother cell

• Tremendous variations are produced• Necessary for sexual reproduction when

progenies are desired to be different than parents

We know from cell theory that cells can come only from pre-existing cells. Mitosis is one of the two types of cell divisions found in living things. The other one is Meiosis.

DNA and their relationship to chromosomes

Cell CycleCell Cycle

Cytokinesis in animal cells by cleavage

Cytokinesis in plant cells by internal plate formation

Can you recognize the phase?

Questions to Ponder• How can the cells in an organism have different form and structure if they all

came from the single cell?

• What was Dr. Yoshio Masui’s contribution to the cancer and cell research?

• Why are most research in cancer directed at cell study?

• What is cancer and how does it spread in the body?

• Why is radiation and chemotherapy applied in cancer treatment? What are their limitation?

• What is meant by haploid and diploid number of chromosomes?