Close examination of an organ reveals a lining of several layers of cells. The layers do not contain any blood vessels and one surface of the cells is open to the internal cavity of the organ. This tissue is probably

Epithelium

Explanation:

Epithelium are tissue massage found mostly in the skin and serve as protective covering for the internal and external parts of the body.

A major characteristic of the epithelium is that its layers do not contain any blood vessels such as the artery or vein. The surface of the cells is also usually open to the internal cavity of the organ.

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.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.