Photosynthesis takes place primarily in the leaves of plants. The structure of the leaf consists of the upper and lower epidermis, the mesophyll, the vascular bundles, and the stomates (Carter). The upper and lower epidermises serve mainly as protection for the leaf, and the stomates only function in air exchange. Carbon dioxide enters through the stomates and oxygen gas exits. The vascular bundles are the plant’s transportation system; all water and nutrients moves via the vascular bundles to different parts of the plant. Chloroplasts are only found in mesophyll, and that is where photosynthesis occurs. The spongy mesophyll layer of a leaf normally contains various gases, like oxygen and carbon dioxide. As a result, leaves float in water. Consequently, if a vacuum is created and the gases are drawn out of the leaf, the leaf would be expected to sink because of its increased density. In order for the leaf to perform photosynthesis, the plant needs access to carbon dioxide as well. Bicarbonate ions dissolved in water would be a way of allowing a leaf to perform photosynthesis while submerged in water. As the leaf performs photosynthesis, however, oxygen is produced and accumulates in the air spaces within the mesophyll. When cellular respiration occurs, oxygen is consumed so the two processes counter each other. Therefore, the oxygen that ends up in the mesophyll after both processes is the net rate of photosynthesis occurring in the tissue. The light source a plant is under greatly affects the rate of photosynthesis. All light and its color variations have a specific wavelength associated with them. A wavelength is defined as the distance from the top of one wave to the top of the next (Russell). Light with wavelengths ranging from 400 – 700 nanometers (nm) is known as visible light (Madigan). The visible colors from shortest to longest in terms of wavelength are as follows: violet, blue, green, yellow, orange, and red. According to scientists like Samuel Pierpont Langley, light with longer wavelengths have the ability to radiate more energy in the form of heat (Madigan). Langley passed light through a prism and discovered that light with a wavelength beyond 700 nm, infrared light, makes other objects warm. To test how the color of a light source affects the rate of photosynthesis in plants, an experiment was performed. If spinach leaves are placed under red, blue, and white light, the plants will have the highest rate of photosynthesis under the red light. This is due to the fact that red light has the longest wavelength of all visible light, allowing it to radiate more energy to the plant. To test this, three medicine cups contained 10 spinach leaf disks each that had air pulled out of their mesophyll layers. These three cups were then placed under varying colored light sources and the rate of photosynthesis was analyzed in the form of net oxygen production.