By Harold McGee
Like animals, plants are built up out of innumerable microscopic chambers called cells. Each cell is surrounded and contained by a thin, balloon-like cell membrane constructed from certain fat-like molecules and proteins, and permeable to water and other small molecules. Immediately inside the membrane is a fluid called the cytoplasm, which is filled with much of the complex chemical machinery necessary to the cell’s growth and function. Then within the cytoplasm float a variety of other membrane-contained bags, each with its own chemical nature. Nearly all plant cells contain a large watery vacuole, which may be filled with enzymes, sugars, acids, proteins, water-soluble pigments, and waste or defensive compounds. Often one large vacuole will fill 90% of the cell volume and squeeze the cytoplasm and nucleus (the body that contains most of the cell’s DNA) up against the cell membrane. Leaf cells contain dozens to hundreds of chloroplasts, bags filled with green chlorophyll and other molecules that do the work of photosynthesis. The cells of fruits often contain chromoplasts, which concentrate yellow, orange, and red pigments that are soluble in fat. And storage cells are often filled with amyloplasts, which hold many granules of the long sugar chains called starch.