Fats have an incredibly high potential to produce a lot of energy when broken down. This is because they are very saturated, which means they have a lot of bonded hydrogens. They also have a lot of carbon-carbon bonds, which have a lot of potential energy stored. When you break down a fat, especially one that has fourteen or more carbons in the chain, you release the energy from every carbon-carbon and carbon-hydrogen bond.

Comparing this to a sugar, alcohol, or protein (amino acids make up proteins), we can see that there aren't as many of these bonds to break. Proteins, in fact, require a lot of energy to break down because they have to be converted into other forms first.

Amphipathic molecules have both a polar and nonpolar region. This amphipathic quality allows phospholipids to create the plasma membrane in eukaryotic cells. The polar region is the phosphate head, which interacts with the aqueous cytosol and extracellular environment. The nonpolar region is the fatty acid tail, which is sequestered in the bilayer of the membrane and helps reduce the permeability to certain molecules.

Water is a very polar substance that will not interact well with nonpolar macromolecules. Enzymes (proteins), oligosaccharides (carbohydrates), and nucleic acids all contain polar regions that make them soluble in aqueous environments. Lipids, however, are hydrocarbons and generally lack a polar region. Lipids would not be soluble in water, but would be soluble in nonpolar organic solvents, like chloroform. We can conclude that cholesterol is a lipid.

Lipids are composed of hydrocarbon chains and are very nonpolar. Polar solvents interact well with polar solutes, but do not solvate nonpolar solutes. When lipids are placed in a polar solvent, they will group together to minimize surface contact with the solvent. These droplets of lipids, or micelles, act like containers for the lipid, keeping them grouped together instead of being distributed through the solvent.

The lipids do not precipitate as they are not necessarily in a solid form. Even lipids in the liquid state can form micelles.

Triglycerides are made up of a glycerol backbone and three fatty acids. They are commonly used to store energy within cells.

A polar head group, a glycerol backbone, and three fatty acids very nearly describes a phospholipid (phospholipids only have two fatty acids). The other answers are not compounds that are readily observed in cells.

Lipids are primarily found in membranes. This includes both the plasma membrane and membranes surrounding particular organelles. Lipids are very useful in membranes because their nonpolar nature helps them act as a barrier between the cell and the outside environment.

Remember that steroids are derived from cholesterol, a four-ringed structure. The four-ringed structure is a constant in all cholesterol-derived molecules. Variation between molecules comes from the final constituent on the four rings.

Plasma membranes are mostly made up of phospholipids. Phospholipids are lipid molecules that contain both polar and nonpolar regions. This amphipathic nature of phospholipids is very important in plasma membranes. Several hormones of the endocrine system are derived from steroids (a type of lipid). Some examples of steroid derived hormones include testosterone, estrogen, and cortisol; therefore, lipids are precursors to molecules in the endocrine system. By definition, unsaturated fatty acids contain carbon-carbon double bonds.

Glycerol is a three-carbon molecule and forms the backbone of triglycerides and phospholipids. Triglycerides have three fatty acids, one attached to each of the carbons in glycerol. Phospholipids use two glycerol carbons to bind fatty acids, and the third to bind a phosphate group.

There are several types of lipids, including fatty acids, phospholipids, sphingolipids, and sterol lipids as well as many more.

Triglycerides fall under the category of glycerolipids and contain a three-carbon glycerol backbone with three fatty acids tails. Phospholipids contain a polar phosphate group, a glycerol backbone, and two fatty acid tails. Sterol lipids contain a four-ring base structure. Cholesterol and steroids are sterol lipids.

Glucose is a monosaccharide (carbohydrate), not a lipid.

Lipids are the fat molecules of biology and are frequently composed of fatty acids. Glycerol is a short 3-carbon chain that is often used to bind different fatty acids together and form lipid structures. When glycerol binds to three fatty acid chains, it forms a triglyceride. Triglycerides are used to store energy in the body.

Phospholipids, which make up the cell membrane, are formed when a glycerol binds to two fatty acids and a phosphate group. Phosphates are complex ions formed from one phosphorus atom and four oxygen atoms: . Steroids are another type of lipid, but do not contain glycerol.

Carbohydrates, proteins, and nucleic acids are the other primary classes of biological macromolecules, and generally do not contain glycerol. Nucleotides are the monomers of nucleic acids and are composed of a pentose sugar, a phosphate group, and a nitrogenous base. Carbohydrates are formed from monosaccharide monomers.