Behaviour of chromosomes in plant and animal cells during mitosis using photomicrographs
Answers
Mitosis is a nuclear division giving rise to genetically identical cells in which the chromosome number is maintained by the exact duplication of chromosome.
Significance of mitosis
production of geneticlly identical cells: It keeps the chromosome number constant and genetic stability in daughter cells, so the linear heredity of an organism is maintained.
growth: a single cell divides repeatedly to produce all the cells in the adult organism
repair of tissue and cell replacement: produce new cells to replace ones that have been damaged (repair and generation of lost parts) or worn out (healing of wouds).
asexual reproduction: a single parent gives rise to genetically identical offspring
Strictly speaking, mitosis is division of the nucleus of the cell. After this, the cell itself usually divides as well (cytokinesis).
The cell cycle
The cell cycle is the continuous cycle of growth and mitotic division. It has 2 major phases: Interfase and Miotic phase.
1. Interphase (between mitotic events) has 3 stages:
G1-phase (Gap 1 phase): cells "monitor" their environment, and when the requisite signals are received, the cells synthesize RNA and proteins to induce growth.
S-phase (Synthesis phase): replication of DNA. Each original chromosome has 1 DNA molecule --> after replication each chromosome has 2 identical DNA molecules (2 chromatids), they are joined together at the centromere.
G2- phase (Gap 2 phase): cells continue to grow and prepare for mitosis. Organelles (mitochondria and chloroplasts) are replicated.
For most of the cell cycle, the cell continues with its normal activities. It also grows (produce new molecules of proteins and other substances --> increase the quantity of cytoplasm in the cell).
2. Miotic phase (M-phase): The mother cell divides into 2 genetically identical daughter cells.
a. Mitosis (nuclear division):
2 chromatids split apart and move to opposite ends of the cell.
A new nuclear envelope forms around each group.
These 2 nuclei each contain a complete set of DNA molecules identical to those in the original (parent) cell.
Mitosis produces 2 genetically identical nuclei from one parent nucleus.
b. Cytokinesis (cell division):
The cell divides into 2 daughter cells (genetically identical to each other and their parent cell).