Shape and pressure come from the plant cell wall
- The idea
- Predict
- See it
- Why
- Check
The idea
“The plasma membrane keeps a plant cell in shape and stops it from bursting.”
Diagrams draw the membrane as the cell's edge, so it seems to hold everything in. In a plant cell, a stiff wall outside it takes the strain.
The short version
The mistake: The plasma membrane keeps a plant cell in shape and stops it from bursting.
What's actually true: The cell wall gives a plant cell its shape, resists water pressure and holds neighbors together. The membrane picks what crosses.
- The cell wall is a stiff mesh of cellulose outside the membrane, so it sets the cell's shape. A shared layer between neighboring walls glues plant cells together.
- In fresh water, water moves in and the cell presses on its wall. The wall presses back. That turgor pressure keeps the cell firm and whole.
- The plasma membrane is thin and flexible, and it controls what crosses. The porous wall lets most small molecules through.
On the exam: Shape, strength and sticking together come from the wall. Choosing what crosses comes from the membrane.