Life at the molecular

• All living organisms are made of atoms of different elements such as sulphur, hydrogen, chlorine, carbon, nitrogen, and potassium
• Some of these elements are essential for the functioning of all living organisms and are called minerals
• Atoms of different elements may combine to form molecules of different compounds such as the various inorganic and organic compounds
• All substances are made of

  • Atoms
  • Elements
  • Compounds
• Organic compounds


  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic acids
  • Vitamins
• Inorganic compounds


  • Water
  • Mineral salts
• Larger organisms are multicellular. The many cells they are composed of arise from existing cells through a type of cell division called mitosis
• The many cells formed by mitosis become specialized and form tissues which perform particular functions
• The various tissues are further arranged to form organs which are also specialized to carry out particular functions
• Minerals


  • Sodium
  • Calcium
  • Potassium
  • Phosphorus
  • Iron
  • Iodine
  • Nitrogen
  • Magnesium
• Sodium


  Maintains osmotic balance in plants, plays a role in the functioning of nerves and muscles, regulates the secretion of HCL in the stomach
• Calcium


  Required for the formation of bone and teeth, blood clotting
• Potassium


  Regulation of blood pressure, nerve functions, muscle control and cellular respiration
• Phosphorus


  Required for the formation of cell membranes, nucleic acids (DNA and RNA), the energy carrier ATP, bones and teeth
• Iron


  Required for the formation of chlorophyll, haemoglobin found in red blood corpuscles
• Iodine


  Required for the formation of the hormone thyroxin secreted by the thyroid gland
• Nitrogen


  Required for formation of amino acids which go to make up proteins, nucleic acids (DNA and RNA), the chlorophyll molecule
• Magnesium


  Forms the central atom of the chlorophyll molecule, required for bone and teeth formation, functioning of nerves and muscles
• When crops are grown and harvested on a regular basis, there may be little time to allow the farms to lie fallow for natural nutrient recycling to take place, so farmers use fertilizers (containing nitrates and phosphates) to quickly replace the nutrients that were used up by the plants
• If too much fertilisers are used, rain causes them to be drained into the streams, rivers, ponds, lakes and into the oceans as well
• The high amount of nutrients in the water, especially nitrates and phosphates, causes algae and other water plants, to grow very rapidly. This is called eutrophication
• The resulting overpopulation of algae or other plants which prefer this rich water supply decreases the ability of light to reach the plants lower down in the water. These plants die and start to rot
• The number of bacteria which bring about decomposition increases, using up large quantities of oxygen. The amount of oxygen available in the water for other organisms decreases, leading to the death of many of them
• Water


  The only substance that exists naturally on Earth in all three states - solid, liquid and gas
• Functions of water


  • Breakdown larger organic compounds into smaller substances
  • Facilitate chemical reactions in cells
  • Transport food down the alimentary canal
  • Transport mineral salts in plants
  • Dissolve waste products produced by the body, forming urine and sweat
• Organic compounds


  • Carbohydrates
  • Lipids
  • Proteins
  • Nucleic acids
  • Vitamins
• Carbohydrates


  Made up of carbon, hydrogen and oxygen, serve as an important energy source, can be broken down in a step-wise fashion to release energy, can be stored as substances like starch and cellulose
• Monosaccharides are simple or single sugars, disaccharides are sugars made up of two monosaccharides, and polysaccharides are carbohydrates made of more than two monosaccharide units
• This activity is meant to test for the presence of starch using iodine solution
• Glucose solution preparation


  1. Make a glucose solution using a spatula and approximately 5ml (5 cm) water in a small test tube

  2. Transfer approximately 2ml of this solution into a small test tube
• Benedict's/Fehling's solution test


  1. Add 4ml of Benedicts Solution (or 2ml of Fehlings Solution A and 2ml Fehlings Solution B) to the test tube

  2. Note the deep blue colour

  3. Place the test tube in a large beaker of hot water

  4. Observe and record any colour changes
• Chalk experiment


  1. Repeat experiment using crushed white chalk

  2. Write down your conclusion from the observations made
• Lipids


  Made up of carbon, hydrogen and oxygen. Lipids may also contain other elements such as phosphorous (as in phospholipids that make up cell membranes) whereas carbohydrates contain carbon, hydrogen and oxygen only. The ratio of hydrogen to oxygen is greater than 2:1 i.e. there are many more hydrogen atoms
• Lipid composition


  Lipids are made up of two kinds of smaller molecules, viz. glycerol and fatty acids. One glycerol molecule combines with three fatty acid molecules, to form a fat molecule. Water molecules are released when this combination takes place
• Types of lipids


  • Saturated fats
  • Unsaturated fats
• Saturated fats


  • Animal fat, butter, lard and beeswax are examples of saturated fats. They are usually solid at room temperature
• Unsaturated fats


  • Most plant fats are unsaturated and they form unsaturated fats. Unsaturated fats are usually liquid at room temperature. Examples of unsaturated fats are olive oil (a plant fat) and fish fat
• Lipid functions


  They are able to store a lot of energy. They act as packing tissue between organs. They reduce heat loss from the body. Phospholipids make up the cell membrane
• Saturated fats, cholesterol and heart disease
• If a person's diet is high in saturated fats, fatty deposits are likely to be formed on the inside of his/her arteries, narrowing the inside of these arteries and slowing down blood flow. High levels of low-density cholesterol appear to increase the formation of these fat deposits inside the arteries