What are those carbohydrates called that cannot be hydrolysed further to give a simpler unit of polyhydroxy aldehyde or ketone?

Monosaccharides

The correct answer is option 1. Monosaccharides.

Let us break down each term and their properties to understand why monosaccharides are the carbohydrates that cannot be hydrolyzed further:

1. Monosaccharides

Monosaccharides are the simplest form of carbohydrates. They consist of a single sugar unit, which means they are the basic building blocks for more complex carbohydrates. Monosaccharides have a basic structure that includes one polyhydroxy aldehyde (aldose) or ketone (ketose) group, along with multiple hydroxyl (-OH) groups. Their general formula is \((\text{CH}_2\text{O})_n\), where \( n \) typically ranges from 3 to 7.

Examples:

Glucose (an aldohexose, a 6-carbon sugar), Fructose (a ketohexose, a 6-carbon sugar), Galactose (an aldohexose, a 6-carbon sugar), etc. 

Monosaccharides cannot be hydrolyzed further because they are the most basic unit of carbohydrates. They are already in their simplest form and do not break down into simpler sugars.

2. Polysaccharides

Polysaccharides are complex carbohydrates composed of long chains of monosaccharide units linked by glycosidic bonds. They are formed through the condensation of multiple monosaccharide units.

Examples:

Starch: A storage form of glucose in plants.

Cellulose: A structural component in plant cell walls.

Glycogen: A storage form of glucose in animals.

Polysaccharides can be hydrolyzed into their component monosaccharides. For example, starch can be broken down into glucose units.

3. Oligosaccharides

Oligosaccharides are carbohydrates consisting of a small number of monosaccharide units (usually 2 to 10) linked by glycosidic bonds.

Examples:

Maltose: Composed of two glucose units (a disaccharide).

Raffinose: Composed of three monosaccharides (a trisaccharide).

Oligosaccharides can be hydrolyzed into their constituent monosaccharides. For example, maltose hydrolyzes into two glucose units.

4. Carbohydrates

Carbohydrates encompass all types of sugars and starches, including monosaccharides, oligosaccharides, and polysaccharides. They are organic compounds consisting of carbon, hydrogen, and oxygen.

Why Monosaccharides Cannot Be Hydrolyzed Further:

Monosaccharides are the simplest form of carbohydrates. They cannot be broken down into simpler carbohydrates because they already represent the basic unit of sugar. They are the fundamental units from which more complex carbohydrates (like oligosaccharides and polysaccharides) are built.

In summary, monosaccharides are the carbohydrates that cannot be hydrolyzed further into simpler units. They are already at the simplest level of carbohydrate structure.