Oligo- Saccharides are those carbohydrates which on hydrolysis yield 2 to 10 monosaccharide units (monomers).
In oligosaccharides, monosaccharides are linked together by glycosidic bonds. Aldehyde or ketone group
of one monosaccharide reacts with alcoholic group of another monosaccharide to form glycosidic bond. One
molecule of `H_2O` eliminates during glycosidic bond formation (dehydration synthesis). Direction of glycosidic
bond is 1'-4".
When another monosaccharide unit is fructose then the direction of linkage is 1'-2". (Non reducing sugars). For
e.g. Sucrose

(i) Disaccharides- composed of two monosaccharide units. e.g. Maltose, Sucrose, Lactose, Trehalose.
# All disaccharides are water soluble and sweet in taste, so they are known as sugar.

# Maltose is commonly called malt sugar. It is intermediate compound in starch digestion. Maltose has 1'
glycosidic linkage between `alpha-D` glucose and `alpha-D` glucose

# Lactose is milk sugar with `beta -1'-4" `glycosidic linkage between glucose and galactose
# Lactose is least sweetest sugar.
# Maximum % of lactose = Human milk ` approx 7%`
# In plants transport of sugar is present in form of sucrose.
# Sucrose is also known as invert sugar.
# Sucrose is called Cane Sugar or Table Sugar or Commercial Sugar. Sucrose composed of `alpha-D` Glucose and
fructose.
# Trehalose is present in haemolymph of insects. It has glycosidic linkage between two anomeric carbon (`alpha-` glucose and `beta-` gluocse).

(ii) Trisaccharides - e.g. Raffi nose ( Calacfose -t-Clucose +Fructose)
(iii) Tetrasaccharides - e.g Stachyose (Gal. + Gal. + Glu. + Fructose)
(iv) Pentasaccharides - e.g Verbascose (Gal. + Gal. + Gal. Gu + Fructose)

Raffinose and stachyose occur in phloem and may be enwloyed for lrcmslocation of carbohydrates.