Answer;
Cell membrane
A cell membrane acts as a boundary that separates things that are inside the system from those that are outside the system.
Explanation;
It is a thin semipermeable structure that surrounds the cytoplasm of a cell.
The membrane functions to protect the integrity of the internal environment of the cell by allowing selective movements of materials in and out of the cell.
The membrane consists of a phospholipid bilayer with proteins embedded in it.
Fat, more specifically, triglyceride which are the main constituents of natural fats and oils in humans and other animals
Because water is a polar molecule, it makes an excellent solvent for polar and ionic compounds found within cells and tissues.
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CO2 is a normal waste that normally diffuse across placenta from embryo to the mother.