Definitions [2]
Define the following term:
Aster
The centrosome (in animal cell) splits into two along with the simultaneous duplication of the centrioles contained in it. The daughter centrioles move apart and occupy opposite "poles" of the cell. Each centriole is surrounded by radiating rays and is termed an aster (aster : star).
Define cell division.
Cell division is one of the most fundamental characteristics of life. This is the method which enables life to perpetuate generation after generation.
Key Points
Key Points: Cell Division
- Cell division is a vital process for growth, repair, and the formation of new organisms, helping maintain life in all living beings.
- It occurs in two forms: mitosis (in somatic and stem cells) for producing diploid identical cells, and meiosis (in germ cells) for forming haploid gametes.
- Mitosis supports body growth and tissue repair, while meiosis ensures genetic variation and maintains chromosome number in reproduction.
- Before division, the cell’s chromosome number doubles (e.g., from 2n to 4n) to ensure accurate distribution during mitosis or meiosis.
Key Points: Significance of Mitosis
- Mitosis is an equational division that produces genetically identical daughter cells, maintaining chromosome number.
- It is responsible for growth in multicellular organisms by increasing the number of cells.
- Mitosis helps in repair, regeneration, and wound healing by replacing damaged or lost cells.
- It maintains the nucleo-cytoplasmic (surface/volume) ratio, which gets disturbed during cell growth.
- Mitosis also enables asexual reproduction in unicellular organisms and continuous cell replacement (e.g., skin, blood, plant meristems).
Key Points: Significance of Meiosis
- Formation of Gametes - Meiosis is responsible for the formation of gametes in sexually reproducing organisms.
- Reduces Chromosome Number - Meiosis reduces the chromosome number by half in gametes, preventing doubling of chromosomes in each generation.
- Restores Chromosome Number - The original chromosome number is restored when gametes fuse during fertilisation.
- Conserves Species-Specific Number - Meiosis ensures that each species maintains its specific chromosome number across generations.
- Genetic Variability - Meiosis increases genetic variability in the population from one generation to the next, which is crucial for the process of evolution.
