Which of these is the largest molecule?

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Question restatement: Which of these is the largest molecule? Options: A polysaccharide; A carbohydrate monomer (eg. Glucose); A phospholipid; An amino acid.

Option 1: A polysaccharide. This is typically a long chain or branched polymer made up of many sugar units. Its size can range from thousands to tens of thousands of atoms, making it substantially larger than the other listed molecules. The polymeric nature and repeated glycosidic linkages contribute to its large molecular weight and complex structure, which is why this option is considered the largest.

Option 2: A carbohydrate monomer (eg. Glucose). A single sugar molecule is relatively small compared to polymers. Its molecular formula is C6H12O6 with a modest molecular weight, so it is much smaller than a polysaccharide composed of many monosaccharide units. Thinking in terms of size, one glucose is simply not as large as polymeric carbohydrates.

Option 3: A phospholipid. Phospholipids are larger than small amino acids or simple sugars but still small relative to polysaccharides when considering overall molecular size. They have a hydrophilic head and hydrophobic tails, and their typical molecular weight is in the range of hundreds to a few thousand Daltons. While sizeable, they do not reach the scale of a long polysaccharide.

Option 4: An amino acid. An amino acid is a small organic molecule with a central carbon, amino group, carboxyl group, and side chain. Its molecular weight is on the order of ~100 Da, which is far smaller than even a single polysaccharide monomer and much smaller than a polysaccharide polymer.

Overall reasoning: When comparing typical molecular scales among these options, polymers formed from repeating units (like polysaccharides) accumulate many monomer units, drastically increasing size and mass relative to monomers (glucose), phospholipids, or amino acids. Thus, the polysaccharide stands out as the largest option.

AGRI10050_2025_SM1 W2 Progress Quiz - Molecular building blocks

Which of these is the largest molecule?

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