Question 1

Why does the plasma membrane need to expand during cell division?

Accepted Answer

A spherical cell requires approximately 1.6 times more surface area to double its volume. Membrane expansion is essential for maintaining the required composition and surface area for cell division. The secretory pathway provides additional membrane through secretory vesicles that bud from the Golgi apparatus and fuse with the plasma membrane during exocytosis.

Question 2

How does membrane growth differ between early and late stages of the cell cycle?

Accepted Answer

In eukaryotic organisms like yeast, plasma membrane expands uniformly during early G1 phase. From late G1 through mitosis, membrane growth becomes polarized to the region where cell separation occurs. Between metaphase and cytokinesis, the plasma membrane surface area increases by approximately 30%.

Question 3

What role does the plasma membrane play in phagocytosis?

Accepted Answer

During phagocytosis, the plasma membrane expands to extend pseudopodia, allowing the cell to change shape and surround particles for engulfment. This membrane enlargement is essential for the cell to engulf foreign materials or pathogens effectively. The expansion provides the additional surface area needed for this process.

Question 4

How does the cell repair membrane damage from wounds?

Accepted Answer

When mechanical stress damages the cell membrane, extracellular calcium enters and triggers regulated exocytosis of lysosomes. Proteins like Lamp1 dock lysosomes to the plasma membrane, while synaptotagmin VII regulates fusion. This process expands the ruptured membrane and helps reseal it.

Question 5

What happens to the plasma membrane during Drosophila cellularization?

Accepted Answer

During cellularization, a syncytium containing 6,000 nuclei surrounded by a single plasma membrane converts into separate epithelial cells. This process requires a 25-fold increase in plasma membrane area. Cytoplasmic vesicles provide the additional membrane needed for this vast expansion of the cell surface.

Question 6

How do organelle membranes contribute to plasma membrane enlargement?

Accepted Answer

The plasma membrane expands when organelle membranes or cytoplasmic vesicles fuse with the cell membrane, adding their molecular components. The fusion of secretory vesicles with the plasma membrane is a major mechanism for increasing membrane surface area and maintaining proper cellular composition during growth.

Question 7

What controls whether a cell can proceed with division?

Accepted Answer

Cell division is precisely controlled so cells divide only after reaching a specific size. This size checkpoint ensures the cell has grown sufficiently and expanded its plasma membrane adequately before cytokinesis begins. The control mechanism prevents premature cell division and ensures proper cellular development.

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