When some substances can pass across them but others cannot biological membranes are said to have?

The biological membranes like the cell membrane or the membrane enclosing the organelles are all semi-permeable. The semi-permeability is the property of membranes that gives them the ability to selectively allow the movement of particles/ solute/ solvent across it. The semi-permeability allows the cell to maintain a concentration gradient across its membrane that further drives various cellular processes within the cell.

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.

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