Which statement about the cell membrane is true?
it contains cellulose and sugars that are involved in communication.
it is present in animal cells only.
it is rigid and elastic for supporting the cell’s shape.
it prevents harmful substances from entering a cell.

It prevents harmful substances from entering a cell. I uses carrier proteins to do so.

The proton has a positive charge while the neutron has no charge they both make up the nucleus of the atom while the elections have a negative charge and surround the nucleus of the atom. the protons and electrons are used to calculate the atom's mass whereas the neutrons don't affect the mass