CHORIONIC VILLI THAT ARE MADE OF CYTOTROPHOBI -AST AND SYNCYTIOT ROPHOBLAST - ARE __ Select one: primary tertiary secondary quaternary

## Step 1<br />The problem is asking us to identify the type of structure that chorionic villi, which are made up of cytotrophoblast and syncytiotrophoblast, represent in the context of biological structures.<br /><br />## Step 2<br />In biology, structures are often categorized into four levels: primary, secondary, tertiary, and quaternary. <br /><br />### **Primary structure** refers to the sequence of amino acids in a protein.<br />### **Secondary structure** refers to the local folded structures that form within a polypeptide due to hydrogen bonding between the backbone atoms.<br />### **Tertiary structure** refers to the overall three-dimensional structure of a single protein molecule.<br />### **Quaternary structure** refers to a protein that consists of two or more separate peptide chains, each with its own tertiary structure, that function as a single protein complex.<br /><br />## Step 3<br />Chorionic villi are structures that develop from the cytotrophoblast and syncytiotrophoblast, which are part of the placenta. They are not a single protein molecule, but rather a complex structure composed of multiple cells. Therefore, they do not represent a primary, secondary, or tertiary structure.<br /><br />## Step 4<br />However, chorionic villi do represent a quaternary structure because they are composed of multiple cells (cytotrophoblast and syncytiotrophoblast) that function together as a single complex.