Use the drop-down menus to identify the terms described below. a group of cells that secretes substances into the blood or directly into an organ a substance produced by cells that specific groups of cells to perform specific functions a channel or tube that conveys a substance

Endocrine gland - a group of cells that secretes substances into the blood or directly into an organ. Differ from exocrine glands, endocrine glands have no ducts and secrete products (hormones) directly into blood.  

Hormone - a substance produced by cells that helps specific groups of cells to perform specific functions. It is a product of endocrine gland which functions as chemical messengers to stimulate other cells.  

Duct – a channel or tube that conveys a substance.  It is part of the exocrine glands (such as salivary glands) which makes contact with surface .

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.