Plato answer:
Stimulation of a neuron causes a change in the charge inside the cell from negative to positive. This change is caused by ions, which are atoms with an electrical charge, moving across the cell. This change within the cell is consistent with the definition of an electric charge.
I suppose it is the density, having more pockets of air in between the granules of sawdust. Air has oxygen. What does a fire need to strive? Oxygen.
28 sex cells the pea plant will have