Cytokinesis as splitting of cytoplasm in a parent cell between daughter cells
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Question
What is cytokinesis?
Answer
The division of the **cytoplasm** to form two separate daughter cells, after mitosis has divided the nucleus.
Question
What is the difference between mitosis and cytokinesis?
Answer
**Mitosis** divides the **nucleus** (chromosomes); **cytokinesis** divides the **cytoplasm** into two cells.
Question
How does cytokinesis happen in an animal cell?
Answer
A **contractile ring** contracts and pulls the membrane inwards, forming a **cleavage furrow** that deepens until the cell is pinched in two.
Question
How does cytokinesis happen in a plant cell?
Answer
**Vesicles** of wall material fuse to form a **cell plate**, which grows **outwards** to the existing walls and divides the cell.
Question
Why do plant cells form a cell plate instead of pinching inwards?
Answer
Plant cells have a rigid **cell wall** that cannot pinch in, so a new wall (cell plate) must be built across the middle.
Question
What is a cleavage furrow?
Answer
A groove formed in an **animal** cell's membrane that deepens until the cell is pinched into two daughter cells.
Question
What is a cell plate?
Answer
A new wall built across the middle of a dividing **plant** cell, growing outwards until it separates the two daughter cells.
Question
Is the cytoplasm usually shared equally between daughter cells?
Answer
**Yes** — in most divisions the cytoplasm is split roughly equally.
Question
Which process is an exception to equal cytoplasm sharing?
Answer
**Egg (gamete) formation** — almost all the cytoplasm goes to one large egg, leaving tiny polar bodies.
Question
What is the mitotic index?
Answer
The proportion of cells that are dividing: **cells in mitosis ÷ total cells counted**.
Question
How do you calculate the mitotic index from a cell count?
Answer
Divide the number of cells **in mitosis** by the **total** number of cells counted (e.g. 30 ÷ 200 = 0.15).
Question
What does a high mitotic index indicate?
Answer
A **large proportion of cells are dividing** → rapidly growing tissue (a meristem), or uncontrolled division in a tumour.
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Topic 4.4 hub
Cell and nuclear division
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