IMAT 2012 Q43 [Molecules]

Which one of the following molecules will contain the greatest number of different elements?

A. amino acids
B. polysaccharide carbohydrates
C. lipids
D. monosaccharide carbohydrates
E. water

The answer to this question is A.

It is important to understand fully what the question is asking for: greatest number of different elements. Thus, keep in mind that you are to not supposed to consider the number of units, atoms, or any form of terms that denote quantity.

Amino acids: The elements contained in amino acids are carbon, hydrogen, oxygen, and nitrogen for a total of 4 different elements. This makes choice A as the answer, as the other choices given contain only 3 or less elements. It is important to note however, that this choice assumes amino acids in general. Which means that you are not supposed to count the presence of sulfur which is present in cysteine and methionine. You are to take “amino acids” in general, and count only the elements that are common to all amino acids.

Carbohydrates: The elements contained in carbohydrates are carbon, hydrogen, and oxygen, for a total of 3 different elements. However, do not be confused by the terms “polysaccharide and monosaccharide”, as these are terms used to denote sugars as units. Monosaccharides are the simplest units of carbohydrates, while polysaccharides are long chains of monosaccharides.

Lipids: The elements that make up lipids are carbon, hydrogen, and oxygen, for a total of 3 different elements. However, do not be too haste to consider this choice if you are thinking of phospholipids that contain phosphorous and nitrogen, since this choice explicitly mentioned lipids. Phospholipids are one of the major types of lipids, which include triglycerides and sterols. Thus, you are to consider “lipids” in general.

Water: The elements contained in water are hydrogen and oxygen, for a total of 2 different elements.

Thus, the correct answer would be choice A, amino acids with 4 different elements.