Choose the statement that explains the difference between the diatom colony and the more advanced Spirogyra. Select one: a. The diatom cells are not interconnected and are very similar to diatoms that are living unicellularly. The Spirogyra cells are the building blocks of the filaments. b. The diatoms are protected by cellulose cell walls. The Spirogyra are protected by silicate shells that could link together to form several larger structures. c. The diatoms are only photosynthetic thanks to symbiotic algae. The Spirogyra have their own chloroplasts. d. The diatoms do not have any specialized structures. The Spirogyra have specialized structures, such as holdfasts and leaves.