Waxes, another common group of simple lipids, contain an alcohol molecule that is larger than the glycerol molecule. Complex lipids have a more complicated structure than simple lipids. Phospholipids are found in all bacteria, and in the cells of all plants and animals. They are most plentiful in sperm, eggs, embryos, and brain cells. A molecule of phospholipid contains a molecule of glycerol, a phosphate ion, and two molecules of fatty acid.
Most phospholipids also have a nitrogen compound.
Some contain inositol, a substance found in vitamin B complex. Steroids make up an important part of living things. Cholesterol, a substance found in the membranes of animal cells, is a steroid. Yeasts and other fungi and the seeds of higher plants also contain steroids. Quinton R. Rogers, Ph.D., Professor of Physiological Chemistry, Univ. of California, Davis.