At the cellular level indicate that the living organisms are made up of the smallest building blocks called cell. It refer to unicellular organisms i.e organism with one cell.
At the cellular level, membranes; for the whole organism, the skin is Reproduction because a single parent cell divides into two cells (offsprings), two divides into four cells and so on. It is called cell division and cell reproduction because a single cell skin divides to produce many cells.
Air pressure is what you measure with a tire gauge. Atmospheric pressure is what you measure with a mercury barometer. Let me be more specific. Pressure is the amount of force per unit area that a gas exerts on a surface.
