(a) a unicellular organism underwent division to produce two cells which are morphologically and genetically similar to the parent. identify which type of the division is involved. explai all the steps along with the diagram.

(b) elaborate the significance of the mitosis and meiosis

(a). Binary fission is a cell division, in which unicellular organism produces two cells which are morphologically and genetically similar to the parent. It represents a mitotic cell division. Here is the complete explanation of mitosis along with diagram.
 

Mitosis (M Phase)

• Also called equational division as number of chromosomes in parent and progeny remain the same

• Mitosis (M phase) is divided into 4 stages.

  • Prophase (1^st stage)

  • Metaphase

  • Anaphase

  • Telophase (Last stage)

Phase	Characteristic features
Prophase	→ Follows G1 and S phases of interphase → Chromosome material condenses and untangles. → Centriole, duplicated during S phase, starts moving towards opposite poles. → Mitotic spindle starts assembling. → Microtubules appear.
Metaphase	→ Chromosomes condense completely. → Sister chromatids held together by centromere → At the surface of centriole, kinetochore appears. Here, spindle fibres attach. → Chromosomes lie at centre (equator) with each sister chromatid attached to spindle fibre of their respective poles with the help of kinetochore. [Alignment is called Metaphase plate]
Anaphase	→ Here, chromosome splits and daughter chromatids separate. → Chromatids move towards opposite poles. → Centromere leads and arms follow.
Telophase	→ Chromosomes reach at opposite poles. → Chromosomes start losing their individuality. → Chromatin material collects at poles. → Nuclear envelope appears around chromosome clusters. → Cell organelles such as ER, Golgi, reappear. → This phase is followed by interphase of next cycle.

Cytokinesis

• Cyto (cell) kinesis (division) follows the process of karyokinesis (nuclear division).

• Process of cytokinesis in plant cell:

  • New cell wall begins to form with precursor cell plate equivalent to middle lamella.

  • This new cell wall grows outwards.

  • Organelles such as mitochondria and plastids also get distributed between two daughter cells at the same time.

• Process of cytokinesis in animal cell:

  • Furrow appears in the cell membrane.

  • This furrow deepens and joins in the centre to divide the cytoplasm.

• If cytokinesis does not follow karyokinesis, then cell becomes multinucleate, leading to the formation of syncytium.

(b)

Significance of mitosis

• Results in formation of diploid genetically identical daughter cells

• Growth of the body takes place by mitosis.

• Cell repair and replacement of worn out tissues

• Maintenance of nucleo-cytoplasmic ratio

• Vegetative reproduction in plants takes place by mitosis​

​Significance of Meiosis

• It results in reduction of chromosome number by half in gametes, which again doubles during fertilization. Therefore, it helps to conserve the chromosome number of species from generation to generation.

• Crossing-over, occurring in pachytene stage of meiosis I, is a source of genetic variability in sexually reproducing organisms.

• The variation thus formed serves as the raw material for evolution.