How do you explain the presence of an aldehydic group in a glucose molecule?

Explanation

Glucose on reacation with bromine water produces gluconic acid. This indicates the presence of `CHO` group.
`overset(" "CHO)overset(|)underset(" "CH_(2)OH)underset(|)(" "(CHOH)_(4))overset(Br_(2)//H_(2)O)rarroverset(" "COOH)overset(|)underset(" ""Glucose acid")underset(" "CH_(2)OH)underset(|)(" "(CHOH)_(4))`