. Principles of modern biology. Biology. ARROWROOT CORN POTATO WHEAT Fig. 4-9. Starch grains from different plants, all drawn to the same scale. soluble in water, but readily soluble in such organic solvents as ether, chloroform, and hot alcohol. Lipids that are liquid at room tem- perature (about 20° C) are commonly called oils (olive oil, cod-liver oil, etc.); but even fats such as butter, lard, and tallow, which are solid or semisolid at room temperature, are generally liquid at the body temperature of the warm-blooded animals in which they occur. Generally the lipid components of the proto
. Principles of modern biology. Biology. ARROWROOT CORN POTATO WHEAT Fig. 4-9. Starch grains from different plants, all drawn to the same scale. soluble in water, but readily soluble in such organic solvents as ether, chloroform, and hot alcohol. Lipids that are liquid at room tem- perature (about 20° C) are commonly called oils (olive oil, cod-liver oil, etc.); but even fats such as butter, lard, and tallow, which are solid or semisolid at room temperature, are generally liquid at the body temperature of the warm-blooded animals in which they occur. Generally the lipid components of the protoplasm are relatively light (low spe- cific gravity) and tend to be thrown to the "light end" when the cell is centrifuged (Fig. 4-10). Because of their diverse chemical nature, lipids are not treated as a single group, but are subdivided into three groups: (1) the true fats, (2) the phospholipids, and (3) the steroids. The True Fats. The true fats include many familiar substances, such as olive oil, butter fat, and beef fat. Beef fat (C57H110O6) shows the typical chemical structure of a true fat in that: (1) true fats are composed en- tirely of C, H, and O; and (2) the natural fats have large molecules, containing usually about 50 and 100 atoms respectively of C and H, but only 6 atoms of O. The fats in protoplasm serve mainly as accessory fuels. However, fats do not oxidize as readily as glucose, although the quantity of energy per gram of oxidized fat is con- siderably greater (9 Cal as compared to 4). Much of the fat in complex animals such as man is localized in special cells, which col- lectively make up the adipose tissue of the body. A molecule of fat represents a combina- tion of simpler units that can be liberated by hydrolysis. In practice this hydrolysis is accomplished by boiling the fat in a strongly basic solution, although cells hydrolyze fats at ordinary temperatures. When hydrolyzed, each fat molecule liberates: (1) one molecule of glycerol, which is
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