Light micrograph of Closterium Sp. , a fresh water unicellular desmid. The cell is divided into two sections (visible here), it has a single nucleus & two chloroplasts, the site of photosynthesis within the cell. The cell walls have an inner layer rich in cellulose and an outer, thickened pectin layer. The pinkish dot visible at each pole is a vacuole containing crystals of gypsum. The term desmids is applied to a group of genera of green algae with a great variety of morphology but who are related by common features of cell structure and method of reproduction. Bright field illumination. Magnification: x 200 at 35mm size.