It's a class of chemical compounds. They are naturally found in plants, and have a foamy appearance.
saponin removes cholesterol from cell membranes, leaving 100 Angstrom "holes" in the membrane, causing the cell to be permeable.
yes, and sometimes it can b very deadly.
Saponin creates 40-50 Å-wide pits in the plasma membrane of a cell.
It has a strong hemolytic effect on the RBC.