Carbohydrates

Carbohydrates contain the following elements; Carbon (C), Hydrogen (H), Oxygen (O)

Structure: Carbohydrates consist of simple sugars. General Formula: (CH₂O)_n , The ration of these elements is generally 1:2:1.

Types of carbohydrate	Reducing sugars	Soluble in water	Example
Monosaccharides (1 sugar unit)	Yes	Yes	Glucose C₆H₁₂O₆(fruit e.g. grapes), fructose (honey, sweet fruits)
Dissacharides (2 sugar units joined together)	Some dissacharides e.g. maltose, lactose (but not sucrose)	Yes	Sucrose (table sugar) lactose (milk), maltose (germinating seeds)
Polysaccharides	No	No	Starch (bread, pasta, potatoes), cellulose (vegetables, wholemeal bread), glycog

Role of carbohydrates in cell structure and metabolism:
- Cell structure: Cellulose forms the structure for plant cell walls, whilst Chitin forms the structure for fungi cell walls and exoskeleton of insects.
- Metabolism:
  Catabolic reactions e.g. respiration

C₆H₁₂O₆ + 6O₂ ->    6CO₂ + 6 H₂O + Energy

         Anabolic reactions e.g. photosynthesis

6CO₂ + 6 H₂O -> C₆H₁₂O₆ + 6O₂

Energy storage: carbohydrates are stored in plants as starch & in animals (muscles and liver) as glycogen