Part (i): Ring form of glucose.
Step 1: The clues.
Pure glucose gives two solids with different melting points and optical rotations that slowly settle to a common value in water (mutarotation), and it fails a few typical aldehyde tests. An open \(-CHO\) chain cannot account for this, so a cyclic structure is proposed.
Step 2: Intramolecular hemiacetal.
The oxygen of the C-5 hydroxyl adds across the C-1 carbonyl within the same molecule. An alcohol adding to an aldehyde gives a hemiacetal; here it produces a six-membered oxygen-containing ring named the pyranose form.
Step 3: Birth of two anomers.
Ring closure turns C-1 into a fresh stereocentre, the anomeric carbon. Its \(-OH\) can point down (\(\alpha\)-D-glucopyranose) or up (\(\beta\)-D-glucopyranose). These two diastereomers are the \(\alpha\) and \(\beta\) anomers, differing only at C-1.
Step 4: Take-away.
Because most glucose stays cyclic, the free \(-CHO\) is scarce, which is why some aldehyde reactions do not occur; equilibrium through the open form allows \(\alpha\) and \(\beta\) to interconvert.
Part (ii): Comparing the two units.
Step 5: Two components vs three.
A nucleoside has just two parts, a nitrogen base linked to a pentose sugar at the sugar's C-1' by an N-glycosidic linkage. Examples: adenosine, cytidine.
Step 6: Adding phosphate.
Attach a phosphate group at the C-5' hydroxyl of that sugar and the unit becomes a nucleotide (three parts: base + sugar + phosphate). Examples: adenosine monophosphate (AMP). Chains of nucleotides joined by phosphodiester bonds make up DNA and RNA.
\[ \boxed{\text{nucleotide} = \text{nucleoside} + \text{phosphate}} \]