Chlamydomonas cells are comprised of a spherical cellulose membrane termed the theca and a superficially located stigma, which is sensitive to light. This eyespot enables the primitive unicellular life form to respond to varying intensities of light and move to regions of higher concentration in order to enhance photosynthesis. Chlamydomonas move by propelling themselves with whip-like movements using two flagella or thread-like appendages, which are especially helpful during certain reproductive phases. A single nucleus is present within the algae cell, however, most of the cell volume is occupied by carbohydrate producing chloroplasts, which manifest in a variety of shapes. This minute organism is typically only ten microns in diameter. Although some cells are solitary, many may aggregate into randomly organized colonies referred to as plamelloid.