3.2 Carbohydrates, lipids and proteins

3.2.1 Distinguish between organic and inorganic compounds:
Living organisms contain many living compounds some are organic others are inorganic. Organic compounds are the once that contain carbon found in living organisms. There are some compounds that contain carbon yet they are inorganic.
  1. Carbon dioxide
  2. carbonates
  3. hydrogen carbonates
All compounds that contain no carbon are inorganic compounds. Carbohydrates, lipids and proteins are found in large amount.
3.2.2 Identify amino acids, glucose, ribose and fatty acids from diagrams showing their structure:

Amino Acid
Fatty Acids


3.2.3 List three examples each of monosaccharide’s disaccharides and polysaccharides:
Examples of monosaccharide:
  • Glucose
  • galactose
  • fractoses
Example of disaccharides:
  • Maltose
  • Lactose
  • Sucrose
Examples of polysaccharides:
  • Starch
  • Glycogen
  • Cellulose

3.2.4 State one function of glucose, lactose and glycogen in animals, and of fructose, sucrose and cellulose in plants:
Examples in animals
Example in plant
Glucose is carried by the blood to transport energy to cells throughout the body
Fructose is used to make fruits sweet-tasting, attracting animals to disperse seeds in the fruit.
Lactose is the sugar in milk that provides energy to young mammals until they are weaned
Sucrose is carried by phloem to transport energy to cells throughout the plant.
Glycogen is used as a short-term energy store in liver and in muscles
Cellulose are used to make strong fiber used to make the plant cell wall.

3.2.5 Outline the role of condensation and hydrolysis in the relationships between monosaccharide’s disaccharides and polysaccharides; between fatty acids, glycerol and triglycerides; and between amino acids and polypeptides:
It is the reaction that builds up stuff: when two materials join together they make larger molecules as well as water E.g.
Amino acid + amino acid = dipeptide + water
The new bond formed is called a peptide linkage.
Polypeptide- proteins:
Further condensation reactions can link amino acids to either ends of a dipeptide forming a long chain at amino acids.
Polysaccharides- carbohydrates:
Condensation reactions can be used to build up carbohydrates and lipids. The basic subunits of carbohydrates are monosaccharide. When two monosaccharides join together they form a disaccharide. When more monosaccharide join together with disaccharides they form polysaccharides.
Triglyceride- lipids:
Fatty acids can be joined to glycerol to form a lipid called glyceride. A max of 3 fatty acids can be liked to each glycerol to form triglyceride.
Hydrolysis reactions:
Large molecules such as polypeptide, polysaccharides and triglyceride can be broken down into smaller molecules by hydrolysis reactions. Water molecules are used in this type pf reaction. Hydrolysis reactions are the reverse of condensation. E.g.
  • Polypeptide + water = dipeptide or amino acids
  • Polysaccharides + water = disaccharide or monosaccharide
  • Gyceride+ water = fatty acid = glycerol

3.2.6 State three functions of lipids:
  1. Energy storage in the form of fat in humans and oil in plants.
  2. Heat insulation: a layer of fat under the skin reduces heat loss.
  3. Buoyancy: lipids are less dense than water so it helps animals to float.

3.2.7 Compare the use of carbohydrates and lipids in energy storage:
  • Carbohydrate and lipids in energy storage
  • Both carbohydrates and lipids have advantages as energy storage in living organisms.
  • Carbohydrates – short periods
  • Lipids- long periods
Advantages of carbohydrates:
  • Carbohydrates are more easily digested than lipids. So the energy stored by them can be released more rapidly.
  • Carbohydrates are soluble in water so they are easier to transport to and from the store.
Advantages of lipids:
  • Lipids contain more energy per gram than carbohydrates, so stores of lipids are lighter than stores of carbohydrates that contain the same amounts of energy.
  • Lipids are insoluble in water, so they do not cause problems with osmosis cells