Summary
Highlights
Living organisms are composed of chemicals, primarily carbohydrates, fats, and proteins, which are organic molecules containing carbon. Carbohydrates, fats, and proteins all contain carbon, hydrogen, and oxygen, while proteins additionally contain nitrogen and sometimes sulfur.
Carbohydrates are large molecules made from simple sugars. Monosaccharides are the simplest form (e.g., glucose). Disaccharides are formed from two sugar molecules (e.g., maltose from two glucose molecules). Polysaccharides are formed from many glucose molecules (e.g., starch, glycogen, cellulose).
Fats are large molecules made from smaller units of fatty acids and glycerol. Their basic unit consists of one glycerol molecule bonded to three fatty acid chains. Fats that are liquid at room temperature are called oils.
Proteins are made of long chains of amino acids joined end-to-end. There are about 20 different amino acids, and their arrangement determines the type of protein formed. Even small changes in the amino acid order result in different proteins.
To test for starch, add iodine solution to the food sample. A positive result is a color change from orange-brown to blue-black.
For reducing sugars, add Benedict's solution to the food sample and heat it in a water bath at 60-70°C for 5 minutes. A positive test results in a color change from blue to orange or brick-red.
To test for proteins, add Biuret solution to the food sample. A positive test shows a color change from blue to violet or purple.
To test for fats and oils, mix the food sample with 2 cm³ of ethanol and shake. Add this mixture to an equal volume of cold distilled water. A positive test results in a cloudy or milky emulsion forming.
To test for Vitamin C, add 1 cm³ of blue DCPIP solution to a test tube, then add a small amount of the food sample solution. A positive test shows the blue color of the dye disappearing.
DNA (deoxyribonucleic acid) contains instructions for growth and development. It consists of two strands wound into a double helix. The strands are held together by hydrogen bonds between pairs of bases: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).