The type of reaction that results in the formation of all macromolecules is called dehydration synthesis.

Here's why:

* Macromolecules are large polymers. Polymers are long chains of repeating subunits called monomers.

* Dehydration synthesis is a chemical reaction where a water molecule is removed from two monomers, linking them together to form a dimer. This process can continue, adding more monomers to the chain, creating a larger polymer.

* Hydrolysis is the opposite of dehydration synthesis. In hydrolysis, a water molecule is added to break the bond between monomers, breaking down the polymer.

Examples of macromolecule formation through dehydration synthesis:

* Carbohydrates: Monosaccharides (simple sugars) are joined together to form disaccharides and polysaccharides (like starch and cellulose).

* Proteins: Amino acids are linked together to form polypeptide chains, which fold into proteins.

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

* Lipids: Fatty acids are linked to glycerol to form triglycerides.

In summary, dehydration synthesis is the key reaction responsible for building all the major classes of macromolecules.