ter can be formed after several reaction steps. The formation of short carbon chain fatty acids is similar in the cells of advanced plants, animals, fungi, bacteria, and algae. For example, in the cell of green algae, the reaction routes of primer such as palmitoleic acid, oleic acid, linoleic acid, linolenic acid in fatty acid synthesis are similar to that in plant cells and yeast cells [27]. The desatura- tion of carbon chain of fatty acid occurs from C18 and further elon- gation of carbon chain takes place to produce long-chain fatty acids which are unusual in normal plant oils (Fig. 2). Long-chain fatty acids (C20–C22) often exist in microalgae and the content varies from species to species [28]. Normally, short-chain fatty acids (C14–C18) which are the main components of biodiesel are majority of fatty acids in Chlorella sp., but high content of long-chain fatty acid and hydrocarbons exist in some specific species of microalgae. So, It is vital to choose proper microalgae species as materials of biodiesel production.