Explanations
Explanations

1.      B     

Isotopes of elements share the same chemical properties as standard elements. They differ only in their number of neutrons, which has no effect on chemistry.

2.      D     

To compute the number of atoms in a compound, add the subscripts in the formula. In this case, 6 + 12 + 6 = 24.

3.      A     

Electrons are shared equally only in nonpolar covalent bonds. In polar covalent bonds, electrons are shared, but their distribution between the partners is unequal. In ionic bonds, one partner hogs all the electrons. Dipole-dipole and hydrogen bonds are weak intermolecular interactions.

4.      D     

Carbon is the element common to all organic compounds. Its unique properties arise from the fact that it can form up to four bonds with other atoms.

5.      B     

Bonds between monosaccharides are formed by dehydration synthesis, a common biochemical reaction in which a new compound is formed by the joining of two monomers with the by-product of water. Hydrolysis is the reverse of dehydration synthesis; “lysis” means breaking, and “hydro” means water, so hydrolysis is the splitting of a polymer with the uptake of a water molecule.

6.      B     

Glycogen is the molecule animals use to store carbohydrates. Plants use starch to store the glucose produced in photosynthesis. Cellulose is also a polysaccharide, but it is a structural component of cell walls. Glucose and fructose are monosaccharides.

7.      D     

The fluid mosaic model states that the cell membrane is made up primarily of phospholipids and proteins. Though cholesterol is found in the membrane, it is not a major constituent.

8.      B     

Nucleotides are made of sugars, phosphates, and nitrogenous bases. Glycerols and fatty acids are part of fats; when these combine with a phosphate, you get phospholipids. Amino groups (NH2) and carboxyl groups (COOH) are found in proteins. Protons, neutrons, and electrons are the basic components of the atom.

9.      E     

Adenine binds only to thymine and uracil. Cytosine binds exclusively to guanine. None of the other answer choices contain correct pairings of nitrogenous bases.

10.      B     

Enzymes cannot work on many different substrates. In fact, the reason enzymes are able to function as they do is because of their specificity in the substrates they can catalyze.

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