Covalent bond is when two atoms share one or more pairs of electrons, an example of this could be H20 or C02.
ionic bonds are when one or more electrons from am atom are removed and attached to another, which can result in positive or negative ions which attract each other, an example of this could be table salt.
For question 3, it would not leak through the whole sandwich because the cell membrane is thick
Lipids don't dissolve in water because of the different polarities. Water is polar and lipids are not polar which is why they don't dissolve. What this means is that they don't bond and don't share electrons and therefore don't mix.
