A community is where a group of people live really close by vs. a population counts how many people live in a area
Well its a little deeper than that. The oxygen transport is made through Hemoglobin (red blood cells) which is pumped from the heart
One function of a plant stem is to transport water and nutrients from the roots to the other parts of the plant such as the leaves.
Another important function of the plant stem, because of its structurally rigid design, is to support the rest of the plant's body.
Plant stems also serve in elevating the leaves of the plant so that they can have better access to sunlight.
I hope this helped!