Final answer:
Tannins contain phenol groups as their functional groups.
Step-by-step explanation:
Tannins are a type of biomolecule found in various plants. They belong to the class of compounds known as polyphenols, which contain multiple phenol groups. Phenol groups are functional groups that consist of an aromatic ring bonded to a hydroxyl (OH) group. Therefore, the functional groups present in tannins are phenol groups.