A longer cell isn't always a bigger cell
- The idea
- Predict
- See it
- Why
- Check
The idea
“The cell that stretches farther is the bigger cell.”
Length is the number you notice first, so it stands in for size. Being thin in two directions can cancel being long in one.
The short version
The mistake: The cell that stretches farther is the bigger cell.
What's actually true: A cell's size is its volume, so a long, thin cell can hold the same amount as a compact one, or less.
- Size means volume. For a box-shaped cell, that's length × width × height, and length is only one of the three.
- At the same volume, a long, thin or flat cell has more membrane than a compact one, so its surface area-to-volume ratio is higher.
- A bigger cell is sure to have a lower ratio only when the shapes match. Otherwise, work out each cell's volume and surface area.
On the exam: Size is volume. Compare volumes, not lengths, before calling a cell bigger.