A scientist observes some cells under a compound microscope and needs to determine if they are bacteria or yeast. Aside from size, what chemical compounds (not organelles!) would positively identify the cell as either a bacterium or a yeast?

The chemical compounds that will help differentiate a yeast from a bacteria is chitin and murein.

Chitin is found in fungi which is the kingdom  yeast belongs to. It is a polysaccharide tightly packed in the exoskeleton and consists of chains of modified glucose known as N-acetylglucosamine.

Murein is a structure  which consists of sugar and amino acids. Murein forms a layer outside the plasma membrane of bacterial cell. Bacteria lacks chitin and Yeast lacks murein which makes it a good way of differentiating between bacteria and yeast.

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chitin and murein

Explanation:

The chemical compounds that distinguish bacteria cell from yeast cell are  

chitin and murein

Chitin is a polysaccharide present in the exoskeleton of fungi made up of chains of modified glucose known as N-acetylglucosamine. N-acetylglucosamine is derived from glucose

While murein is a mesh like structure made up of sugar and amino acids. Murein forms a layer outside the plasma membrane of bacterial cell.  

since there are no options posted i'll give you a few examples.

a dolphin's flipper, bird's wing, cat's leg.