Falsecolour transmission electron micrograph TEM of a cell in the root tip of a maize plant Zea mays Plant cells are distinct from animal cells in having an additional external envelope the plant cell wall outside the plasma membrane In this micrograph the cell wall made of proteins polysaccharides appears as the thin layer between the cells The wall defines the shape of the cell expands as it grows The prom inent round organelle in the cell is the nucleus which contains a smaller red nucleolus The yellow areas in the cytoplasm are vacuoles Magn ification x at mm size x at xcm size Reference MICROCOSMOS figure page