Organisms are all made of Carbohydrates, Proteins, Lipids, Steroids and Nucleic acids. Organisms all have metabolic pathways. Organisms are open systems that interact continuously with their environment. Organisms transform energy. Darwin observed that individuals in a population vary greatly in their heritable traits and he observed an overproduction of individuals creating a situation where not all can possibly survive, thus a struggle for existence.
Animals evolve through time.
There is a tremendous struggle for existence among all organisms. Individuals with appropriate variations are the ones that leave more offspring. A buffer a. maintains pH at a value of 7. Cellulose a. is a polypeptide made of many monomers. A glucose molecule is to starch as a. a steroid is to a lipid.