Phenol red is a biological indicator used to monitor changes in pH. The phenol red indicator changes color ranging from yellow to pink with respect to changes in pH. In an acidic pH i.e. <7, the phenol red changes to a YELLOW color while in an alkaline pH i.e. >7, the phenol red changes to a PINK pH.
The presence of carbon dioxide (CO2) increases the hydrogen ion concentration (H+) of a solution (lowering its pH or making it acidic).
Therefore, in a reaction where CO2 is created as a product, it means the CO2 content of that solution increases. Hence, the phenol red solution will be shifting towards the YELLOW color in response to a decreasee in pH (acidic).
Despite their frequency in the intertidal zone, in tide pools, sea urchins can be found at many different depths and in any habitats. They can also be found in nearly any ocean temperature. Sea urchins inhabit the polar seas as well as the warm tropics.
