Rigid, but not sealed

The idea

Although rigid, the cell wall is permeable to water and some dissolved minerals; together with the selectively permeable cell membrane, this lets plant roots absorb water and nutrients from the soil.

A thirsty root

A plant root is surrounded by a rigid cell wall. Yet it must take in water and minerals from the soil.

How can a rigid wall let water in?

• The wall is permeable: water and some dissolved minerals pass through it
• It cannot; roots take in water some other way
• The wall is not rigid at all

Soil to root

Send different things from the soil. See where each one is stopped.

Wall and membrane work as a team

Although rigid, the cell wall is permeable: water and some dissolved minerals can pass through it. Together with the selectively permeable cell membrane, this helps plant roots absorb water and nutrients from the soil.

Wall first, membrane second: the wall does not choose, the membrane does.

• Layer | What it does
• Cell wall | permeable: water and dissolved minerals pass
• Cell membrane | selective: lets in what the cell needs

Notes

The cell wall is permeable to water and some dissolved minerals. With the selectively permeable membrane it lets roots absorb water and nutrients from the soil.

Check yourself

The cell wall is…

Which layer chooses what enters the cell?

How do plant roots absorb water and nutrients from soil?

A large soil grain touches a root cell. What happens?

• permeable to water and some dissolved minerals — correct. Yes.
• completely sealed. Then roots could not take in water.
• selective, like the membrane. The selective layer is the membrane.
• The cell membrane — correct. Yes. It is selectively permeable.
• The cell wall. The wall is permeable to water and minerals; it does not choose.
• The soil. The soil does not choose.
• Through the permeable wall and the selectively permeable membrane together — correct. Yes.
• Through the wall alone. The membrane is needed to choose.
• Through the membrane alone, with no wall. Plant cells have a wall outside the membrane.
• It cannot pass through the wall — correct. Yes. Only water and dissolved substances pass the wall.
• It passes through the wall easily. It is far too big.
• It dissolves into the cell. A grain does not enter the cell.