The end product of protein digestion is:a.glycerolsb.protein moleculesc.peptidesd.amino acids

The end product of protein digestion is: d. amino acids

Here's the step-by-step process:

1. Proteins in the food we eat are broken down into smaller pieces, or peptides, by enzymes in our stomach and small intestine.

2. These peptides are then broken down further into their building blocks, which are known as amino acids.

3. These amino acids can then be absorbed through the small intestine into the bloodstream, where they can be used by our bodies to build and repair tissues, among other things.

So, the end product of protein digestion is amino acids.