Question

you are given four test - tubes containing purified biological molecules. the test - tubes are unlabeled except for a number between 1 and 4. you are told that one test - tube contains a protein, one contains a lipid, one contains a carbohydrate, and one contains a nucleic acid. you then perform some tests on the macromolecules and collect the following information. 1) test tubes #2 and #4 contain nitrogen, but the other tubes do not. 2) the contents of test tube #3 are not soluble in water, but the contents of the other test tubes are soluble in water. 3) the contents of test tube #1 can be broken down into subunits that are exactly identical to each other. 4) the macromolecules in test tube #2 is found to have a globular shape. what is the identity of the macromolecule in test tube #2? a) lipid b) nucleic acid c) carbohydrate d) protein

Explanation:

1. Lipids: Lipids are insoluble in water, which matches the description of test - tube #3.
2. Nucleic acids: One test - tube contains a nucleic acid as given in the problem statement.
3. Carbohydrates: Carbohydrates can be soluble in water and some can have simple subunits. But the key here is the description of test - tube #1 being broken down into identical subunits which is more characteristic of proteins.
4. Proteins: Proteins can have a globular shape and can be broken down into subunits (amino - acids) that are identical to each other. Test - tube #2 has a globular shape and can be broken down into identical subunits, so it is a protein.

Answer:

D. Protein