Cytokinesis
சைட்டோகைனசிஸ்
Karyokinesis without cytokinesis is a biological disaster. It creates a syncytium, a single cell with multiple nuclei. In the human body, this is a pathological state, not a functional one.
The idea
Cytokinesis is the physical division of the cytoplasm into two daughter cells. In animal cells, this occurs via the appearance of a furrow in the plasma membrane, which deepens centripetally. In plant cells, it occurs by the formation of a cell plate that grows centrifugally from the center to the walls. This process marks the final completion of cell division.
Why it matters
It physically separates the two newly formed nuclei into distinct, independent daughter cells.
NEET lens
NEET focuses on the contrast between animal and plant cytokinesis. Remember: animal cells use centripetal furrowing; plant cells use centrifugal cell plate formation. Do not confuse the cell plate with the middle lamella; the cell plate is the precursor. Expect a 'Match the Following' or 'Correct Statement' question on this mechanism.
Clinical significance
Failure of cytokinesis in human zygotes leads to polyploidy, which is incompatible with life. In cancer cells, uncontrolled cytokinesis or its failure contributes to genomic instability and aneuploidy. Precise regulation is the only barrier between healthy tissue and malignancy.
Introduction
Cytokinesis is the physical process of cytoplasmic division following karyokinesis (nuclear division), resulting in two separate daughter cells. It differs between plant and animal cells.
Core concept
Animal cells: cleavage furrow forms. Actin-myosin contractile ring assembles at the cell equator → constricts inward → pinches cell in two (centripetal). Plant cells: cell plate forms. Golgi vesicles containing cell wall materials (pectin, cellulose precursors) migrate to cell equator along phragmoplast (spindle remnant microtubules) → fuse from center outward (centrifugal) → new cell wall between daughter cells.
Go deeper
Phragmoplast: spindle fiber remnants that guide vesicle trafficking to the cell plate in plants. Acts like a railway track. The cell plate begins in the center and grows outward to the existing cell wall — opposite of animal cleavage which starts at the outside.
From Class 10
After the nucleus divides, the cell cytoplasm also needs to split into two. This splitting of the cytoplasm is called cytokinesis.