Cheek cells. Light micrograph of squamous epithelium cells from the inside of a human cheek. The nuclei (round), which contain the cell's genetic information, are seen within each cell's granular cytoplasm. Epithelial tissues cover all body surfaces, external and internal, apart from the blood and lymph vessels. These cells form a protective layer in the mouth. Cheek cells are often used for DNA (deoxyribonucleic acid) tests. Magnification: x700 when printed at 10 centimetres wide.