Page 13 - E-Biology Sec.2 2024-2025 U1_Handy

2. Selective permeability
phenomenon

The semi-permeable plasma membrane selects and allows some ions to pass while
other aren’t permitted according to the plant requirements only .

not their size / conc. / charge.

3. Active transport
phenomenon

Moving of ions from low conc. med. Plasma membrane high conc. med. inside

the cell with the help of chemical energy which is needed to force the ions to move

against this conc. gradient.

Nitella algae live in swamps and prove the occurrence of active transport:

1- The conc. of ions in its cellular sap is higher than that in swamp, so

the cell uses energy to absorb these ions.
2- The conc. of some ions in 1 cellular sap is higher than the other cells, so the ions

are selectively absorbed according to the cell’s requirements.

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First Term