The correct answer is A. Complex macromolecules are formed via condensation reactions (also called dehydration synthesis), named for the fact that water is produced as a byproduct. Hydrolysis reactions involve break down of complex molecules into simpler ones and require an input of water. Condensation reactions are endergonic (require energy input) rather than exergonic. Condensation reactions are anabolic rather than cataboic reactions.

C is the correct answer. Phosphodiester bonds are formed via condensation reactions between the ribose on one nucleotide monomer and the phosphate on another. They form the sides of the DNA double helix ladder. In DNA, hydrogen bonds between nitrogenous bases form the "rungs" of the DNA double helix ladder. RNA, a single-stranded molecule, lacks these bonds. Peptide bonds between amino acid monomers form proteins. Glycosidic bonds are found in carbohydrates.

C is the correct answer. A hexose contains 6 carbons. The prefix aldo refers to presence of an aldehyde functional group. A 3-carbon sugar is called a triose. Glucose is a monosaccharide, a carbohydrate monomer, and therefore cannot be composed of monomers.

A is the correct answer. Both cellulose and chitin form lattice-like structures when adjacent chains of linked monomers form hydrogen bonds with each other. Both molecules are carbohydrates and do not contain protein myofibrils. Both have glycosidic bonds, but they are not what produce the stable structural latticework. Acetylamino groups are found in chitin but not cellulose. Cellulose interacts with lignin in plant cell walls to give plants structural support.

The correct answer is D. Phospholipids are composed of long, fatty-acid chains bonded to a phosphate head. This forms a polar structure with a high hydrophilic phosphate head and hydrophobic fatty-acid tails. The polar phosphate heads repel each other, such that molecules line up with hydrophilic heads facing outward, toward water in solution. The hydrophobic tails line up away from the watery solution facing inward such that a bilayer of molecules will spontaneously form in solution. Intermembrane proteins do not influence the alignment of phospholipids in membranes.

C is the correct answer. Primary protein structure is the result of peptide bonds between amino acid monomers. Seocndary structure results when hydrophobic amino acids are turned toward the inside of the molecule away from a watery exterior. Bonding of multiple polypeptides produces quaternary structure.

The correct answer is D. The degree to which enzymes affect chemical reaction rates is described by the Michaelis-Menten equation. Allele frequencies are described by the Hardy-Weinberg equation. Although antibodies are specific for the antigens they neutralize, there is no equation to describe that specificity. Enzymes function by lowering the activation energy necessary to get a chemical reaction to go.

C is the correct answer. Although pH and temperature both affect enzyme activity, these are not mechanisms used by cells to regulate enzyme activity. Cells regulate enzymes via allosteric inhibitors and activators, as well as by feedback inhibition. Substrates bind at enzyme active sites, regulators do not.

he correct answer is A. Cytosine, thymine, and uracil are all single-ringed pyrimidines. Adenine and guanine are double-ringed purines.

A is the correct answer. Unsaturated fats are those that contain at least one carbon double bond. They are unsaturated because they do not contain the maximum number of H atoms possible. A polyunsaturated fat has more than one double bond. The bending of fatty acids in unsaturated fats (or oils) makes them liquid at room temperature. Saturated fats are solid at room temperature.

The correct answer is D. Lipoproteins transport cholesterol and other steroids throughout the body. Antibodies are proteins important in immunity; they act by binding to neutralizing antigens. Cholesterol is a steroid, as are some kinds of hormones. Phospholipids are the primary structural component of cell membranes.

B is the correct answer. Amino acids are composed of an amine and a carboxyl group bonded to either end of one or more carbons (the R group). Carboxyl functional groups contain a C double-bonded to an O and single-bonded to an OH. The hydroxyl portion of the carboxyl group often gives up H ions in solution, defining the acid nature of amino acids.