Introduction:
Polysaccharides are complex carbohydrates composed of repeating units of monosaccharides. These monosaccharides are linked together by a specific type of bond known as the glycosidic linkage. The glycosidic linkage is a covalent bond formed between the anomeric carbon of one monosaccharide and a hydroxyl group on another monosaccharide. It is the key structural feature that gives polysaccharides their unique properties and functions.

Explanation:
The correct answer is option 'D', the glycosidic linkage. Let's understand why this is the correct answer and explore the other options:

1. Peptide linkage:
- Peptide linkages are covalent bonds that connect amino acids to form proteins.
- Polysaccharides are not formed by peptide linkages, so this option is incorrect.

2. Glycogen linkage:
- Glycogen is a storage polysaccharide found in animals, including humans.
- While glycogen is composed of glucose monomers, the linkage connecting these monomers is the glycosidic linkage, not the glycogen linkage.
- Therefore, this option is incorrect.

3. Nucleosidic linkage:
- Nucleosidic linkages are covalent bonds that connect nucleotides to form nucleic acids, such as DNA and RNA.
- Polysaccharides are not formed by nucleosidic linkages, so this option is incorrect.

The Glycosidic Linkage:
The glycosidic linkage is a specific type of covalent bond formed between the anomeric carbon of one monosaccharide and a hydroxyl group on another monosaccharide. It is formed through a condensation reaction, where a molecule of water is eliminated.
- The anomeric carbon is the carbon atom that is involved in forming the ring structure of a monosaccharide.
- The hydroxyl group can be located on a different monosaccharide or on the same monosaccharide, resulting in different types of glycosidic linkages.

Properties and Functions:
The glycosidic linkage plays a crucial role in determining the properties and functions of polysaccharides:
- The type of glycosidic linkage determines the structure and shape of the polysaccharide molecule.
- It affects the solubility, digestibility, and stability of the polysaccharide.
- Different types of glycosidic linkages result in different polysaccharides with distinct functions, such as energy storage (e.g., starch, glycogen) or structural support (e.g., cellulose, chitin).

Conclusion:
In polysaccharides, the linkage connecting monosaccharides is called the glycosidic linkage. This covalent bond is formed between the anomeric carbon of one monosaccharide and a hydroxyl group on another monosaccharide. The glycosidic linkage determines the structure, properties, and functions of polysaccharides.