Identifying Organic Compounds in Plants


A. Carbohydrates

Simple Sugars

Benedict's Solution (alkaline solution of copper sulfate) will react when heated in the presence of simple sugars to form a red precipitate.


I2KI (Solution of elemental ioding and potassium iodide) will become opaque purple in the presence of starch

  • Link to positive starch test in a corn grain

B. Lipids

Sudan IV: this stain is dissolved in alchohol. It has a greater affinity for nonpolar compounds than for polar compounds like water. It will diffuse into plant tissues containing lipids and color them light red.

  • Link to photomicrograph of peanut tissue testing positive for lipids

C. Proteins

Concentrated Nitric Acid: will react to phenolic "R" groups on amino acids to form a yellowish product. When followed by a treatment with Ammonium Hydroxide, will form an orangish color.

  • Link to positive protein test in a corn grain

C. Nucleic Acids

DNA: In lab we extracted DNA from wheat germ.

  • Link to view extracted DNA