Which characteristics makes a cell membrane selectively preamble

Did you mean permeable?

The hydrophobic center to a cell membrane (also known as a phospholipid bilayer) gives the membrane selective permeability.  If a substance is permeable , something such as water or gas can pass through it or soak.

Some solutes cross the membrane freely, some cross with assistance, and others do not cross at all.

Large molecules do not cross intact cell membranes, except in certain special cases.

Cells are selectively permeable due to the Phospolipid Bilayer. It allows only certain molecules to pass through. The cell membrane is made of two sheets of phosolipid bilayers

parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.

the missing space is phylum