Polymers are molecules that are made of two or more repeating units of the same molecule or atom. For example, a polysaccharide is made of two or more monosaccharides bonded by dehydration synthesis. Lipids, on the other hand, are not. For example, triglycerides are composed of a glycerol molecule covalently bonded to three fatty acids via dehydration synthesis; however, fatty acids are elongated by the addition of methyl groups to the fatty acid chain. 

Lipids are a diverse group of organic compounds containing 4-28 carbons. Lipids include fats, cholesterols, and vitamins. Lipids have a hydrophilic region with a polar carboxyl group and a hydrophobic region with a non-polar hydrocarbon chain. Lipids can be either saturated fatty acids (i.e. no double bonds) or unsaturated (i.e. one or more double bonds). The double bonds add a kink and reduce the melting point. Glycogen is a polysaccharide that is used for energy storage in animals. 

Glycogen is a polysaccharide made by animals for energy storage. If it is not used, then it will be converted to fat for more permanent storage. Starch is a polysaccharide that functions as plant storage. The polysaccharide cellulose provides structure to plants. Glucose is a ubiquitous fuel source used by most organisms in some of the following ways: aerobic respiration, fermentation, or anaerobic respiration. Glucose is also the product of photosynthesis. 

Maltose is a type of disaccharide that consists of two molecules of the monosaccharide glucose. Monosaccharides come together to produce a disaccharide and a molecule of water: condensation reaction. Polysaccharides include starch, glycogen, and cellulose. Starch is responsible for plant energy storage and includes amylose and amylopectin. Glycogen is used in animals for energy storage. Cellulose is a structural molecule utilized in plants. 

Monosaccharides come together to produce a disaccharide and a molecule of water. Lactose is a disaccharide that consists of a molecule of the monosaccharides glucose and galactose. Maltose is a type of disaccharide that consists of two molecules of the monosaccharide glucose. Sucrose is a disaccharide that consists of a molecule of both the monosaccharides glucose and fructose.

Vitamins A, D, E, K are all fat-soluble vitamins. Fat-soluble vitamins are absorbed through the intestinal tract with the help of fat (i.e. lipids). Because these vitamins are not water-soluble they are not excreted in urine and thus are more likely to accumulate in the body, leading to hypervitaminosis (i.e. excess amounts of vitamins A, D, E, and K can lead to health consequences.). Vitamin C is water-soluble and is excreted in urine; therefore, regular intake is important.

Humans can obtain vitamins from a variety of mechanisms. Diet—consumption of food—is an intuitive resource that provides humans with vitamins; however, there are certain vitamins that are obtained by other means. Intestinal microorganisms help us produce both vitamin K (a fat soluble vitamin) and biotin. After exposure to sunlight’s natural ultraviolet light vitamin D is synthesized within the skin. Vitamin deficiencies can be very serious and include the following disorders: rickets, beriberi, scurvy, and night-blindness. 

Cholesterol is the precursor to all steroid hormones. Cholesterol is used as a structural component in cell membranes. It is also a precursor for many hormones—including testosterone and progesterone—and vitamins. Cholesterol is involved in cell communication including: intracellular transport, cell signaling, and nerve conduction. There are two primary types of cholesterol: LDL and HDL.

Phospholipids are a type of complex lipid. They consist of a glycerol, two fatty acids, and a polar phosphate group with an alcohol. Their function is to create cell membranes, specifically the fluid mosaic model. They have a polar "head" and a non-polar "tail." The head is hydrophilic ("water loving"), and the tail is hydrophobic ("water hating"), making it perfect for making membranes. 

Carbohydrates are composed of carbon, hydrogen, and oxygen. Carbohydrates include sugars, starches, cellulose, and chitin. Carbohydrates can be organized into four chemical groups including: monosaccharides, disaccharides, oligosaccharides, and polysaccharides. The small carbohydrates called monosaccharides and disaccharides are typically referred to as sugars. Carbohydrates perform many roles in living organisms most notably energy and structural components (e.g. cellulose and chitin).