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Testing for Plant Macromolecules
Detect the presence of carbohydrates, proteins, and lipids in seeds and seed products, fruits, and
vegetables (roots, stems, leaves) at the macroscopic scale.
Determine the percent of total food calories contributed by lipids. by protein, or by carbohydrate, given
food label information.
Text Reading You Should Do Before Beginning This Lab
Chapter 2 in Stern's Introductory Plant Biology, 12" ed. (or 13" ed.) by Bidlack and Jansky.
What You'll Need to Turn in For This Lab:
The first page (this page!), with your name and email address, pages 5, 7, 9-11 of the lab unit, and two
photographs that have been electronically embedded into an MS Word document and labeled
appropriately. If you are using a film camera, the photos should be developed and affixed to a sheet of paper
with appropriate labeling provided on the paper.
Plant foods are substances containing large (macro-) molecules. Macromolecules can be broken down into their
molecular subunits (smaller molecules). The subunits may provide an organism with structural or functional
components of cells, or may be further broken down to provide energy. Three very important kinds of
macromolecules are carbohydrates, proteins, and lipids.
Carbohydrates are composed of simple sugar subunits. Proteins are specific sequences of amino acids. Lipids
consist of glycerol and various fatty acids. Each of these subunits is composed of some combination of Carbon,
Hydrogen, and Oxygen atoms. The bonds between the atoms represent stored chemical energy.
Because molecules of sugars, amino acids, and fatty acids contain different configurations of C, H, and O, they
will contain different amounts of energy. When they are broken down in cells by the process of respiration, they
yield their energy up as newly made molecules of ATP or other energy carrying compounds. When they are
combusted, their energy is released as heat, in the form we know as calories. A calorie (note lowercase "c') is
the amount of heat required to raise the temperature of 1 ml of water by 1"C, at normal temperatures and
pressure. A Calorie (uppercase "C") is 1000 calories, also known as a Kilocalorie (Kcal). In general,
carbohydrates produce an average of 3.9 Kcal/g, compared with 3.5 Kealg for proteins. Lipids, on average,
produce about 9.3 Keallg. Because of their relatively lager size, lipids contain the most potential energy.
Seeds contain macromolecules that store energy and cellular building blocks that can be used during seed
nation and initial seedling growth. Seeds of some species contain large amounts of carbohydrates. Other
senad contain large amounts of proteins or lipids. Since the three different macromolecules yield different
mounts of Kcallg. then seeds of different species will contain different Kcal/g. Humans and animals can use
this energy from seeds.
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- Fall '07
- Energy, Plant Macromolecules