starch,fats,proteins

• Complex carbohydrate


  Made up of many similar molecules of single sugar joined together to form a large molecule
• Types of complex carbohydrates

  • Starch
  • Cellulose
  • Glycogen
• Starch


  • A starch molecule is made up of several thousand glucose molecules joined together
• Cellulose


  • A cellulose molecule is made up of many glucose molecules joined together. The bonds between glucose units are different from that in starch
• Glycogen


  • Glycogen is a branched molecule. It is made up of many glucose molecules joined together
• Role of starch


  It is a storage form of carbohydrates in plants. When needed, it can be digested to glucose to provide energy for cell activities
• Role of cellulose


  The cellulose cell wall protects plant cells from bursting or damage. Cellulose cannot be digested in our intestines. They serve as dietary fibre that prevents constipation
• Role of glycogen


  It is a storage form of carbohydrates in mammals. When needed, it is digested to glucose to provide energy for cell activities
• Plants store glucose in the form of starch. Animals cannot make or store starch in their bodies</b>
• In animals, the main store of glucose is glycogen. Glycogen is sometimes called 'animal starch'
• Glycogen is stored mainly in the liver and the muscles of mammals
• Reasons why glycogen and starch are suitable as storage materials in cells

  • They are insoluble in water, so they do not change the water potential in the cells
  • They are large molecules that cannot diffuse through cell membranes, so they will not be lost from the cell
  • They can easily be easily broken down to glucose when needed, for example, in tissue respiration
  • Their molecules have compact shapes, so they occupy less space than all the individual glucose molecules that make up a glycogen or starch molecule
• Breakdown of starch


  1. Starch in the foods we eat may be digested in our alimentary canal

  2. The enzyme amylase digests starch to form the sugar maltose

  3. Amylase cannot break maltose down to glucose

  4. Maltose is hydrolysed to glucose by another enzyme, maltase

  5. Complete digestion of starch gives glucose molecules
• Polypeptide


  Many amino acid molecules are joined in a linear manner to form a polypeptide
• Protein


  A protein molecule is made up of one or more polypeptide chains folded together
• In most proteins, the polypeptide chains are folded into a more complex, three-dimensional shape