A changed rate doesn't prove membrane damage
- The idea
- Predict
- See it
- Why
- Check
The idea
“If a treatment changes how fast something enters a cell, it must have damaged the membrane.”
Harsh treatments can tear membranes, so a leak is the easy guess when a rate changes. But a leak makes predictions, and the data often break them.
The short version
The mistake: If a treatment changes how fast something enters a cell, it must have damaged the membrane.
What's actually true: A leak lets molecules through both ways without choosing between them, so it can't pile one up above the outside level.
- A damaged membrane leaks, and a leak lets molecules move both ways. Net movement stops when inside matches outside, so the inside can't go higher.
- Building a molecule up against its gradient takes active transport by a pump or cotransporter, or trapping it inside. Both need an intact membrane.
- A hole also doesn't choose, so molecules of similar size should leak in too.
- Harm usually grows with dose, too. A rate that levels off and holds steady points to some other limiting factor.
On the exam: A leak evens things out, lets similar molecules in, and worsens with dose. Check for all three.