A plant is made up of microscopic living structures called cells. Like animal cells, plant cells have a nucleus and an oily membrane surrounding the whole cell. A plant cell is also encased in a tough cell wall and usually contains a large, fluid-filled bubble called a vacuole.he stem is the main support of the upright plant, and connects the roots and leaves. It contains bundles of microscopic tubes – xylem vessels, carrying water and minerals, and phloem vessels, carrying food. The stem also has cells with special thickened walls that help to provide strength.