Hydrogen and hydroxyl (OH) are removed during dehydration synthesis because they are used to form a water molecule (H₂O). This is the core principle of dehydration synthesis:

* Two monomers (smaller molecules) are joined together.

* One monomer loses a hydrogen atom (H) and the other loses a hydroxyl group (OH).

* The hydrogen and hydroxyl combine to form a water molecule (H₂O).

* The remaining portions of the monomers join together, forming a larger molecule called a dimer.

Here's a simplified breakdown:

Monomer 1 + Monomer 2 → Dimer + H₂O

This process is crucial for building complex molecules like:

* Carbohydrates: Sugars like glucose are joined together to form complex carbohydrates like starch and cellulose.

* Proteins: Amino acids are linked together to form long chains of proteins.

* Nucleic acids: Nucleotides are joined together to form DNA and RNA.

Essentially, dehydration synthesis is like using a "water bridge" to join two molecules, and the water molecule is the "bridge" itself.