(1) they keep toxic substances out of the cell;
(2) they contain receptors and channels that allow specific molecules, such as ions, nutrients, wastes, and metabolic products, that mediate cellular and extracellular activities to pass between organelles and between the cell and the outside environment;
(3) they separate vital but incompatible metabolic processes conducted within organelles.
A virus is not a bacteria, but it is caused by a bacteria. A virus causes the immune system to weaken.
Atom refers to a tiny particle, which is the basic building block of all the substances and whose properties determine the characteristics of an element made up of only of those atoms.
All the living and nonliving matter in this world are made up of atoms and elements. Everything in the universe is matter, and matter comprises elements. Some of the elements are important to living things.
Elements are formed by atoms, and atoms comprise protons, electrons, and neutrons. The number of protons in an element's atom signifies the identity of the element.
