some of the special structures in the members of these phylum as follows:
Members of porifera are sponges. they have collar cells and cellular -level body organization. Cnidarian have stinging cells present on the tentacles around the mouth. Ctenophorans have comb-like plate cells for swimming. Platyhelminthes - members are first to have sensory and nervous tissue in the head region.
The cell membrane's main trait is its selective permeability, which means that it allows some substances to cross it easily, but not others.
<em><u>Small molecules that are non-polar (have no charge) can cross the membrane easily through diffusion, but ions (charged molecules) and larger molecules typically cannot.</u></em>
Charged ions such as N+ and K+ Cannot permeate the cell membrane for the since uncharged molecules repel uncharged molecules present in the membrane structure.
