Spinghomyelin has a head group of phosphotidylcholine, which makes sphingomyelin a phospholipid. None of the other lipids have phosphates, and therefore are not phospholipids. 

To answer this question we need to recall the structure of the different macromolecules. Proteins are made up of amino acids, nucleic acids are made up of nitrogenous bases, phosphate groups and 5-carbon sugars, carbohydrates are made up of monosaccharides, and most of the lipids are made up of a three-carbon glycerol molecule attached to varying numbers of fatty acids and other molecules. If there are three fatty acids attached to three of the carbons of glycerol, then it is classified as a triglyceride. If there are two fatty acids and a phosphate group, then it is a phospholipid; therefore, the molecule mentioned in this question is phospholipid. Recall that phospholipids are mainly found in cellular membranes, such as plasma membrane.

Note that certain lipids such as cholesterol and sphingolipids don’t have 3-carbon backbone molecule with fatty acids. They are organized in a different manner. Cholesterol is a ring structure with four rings and hydroxyl group whereas sphingolipids are synthesized from sphingosine.

Recall that there are four main nonpolar vitamins (lipids): vitamins A, D, E, and K. Vitamin A is an important vitamin for proper functioning of eye and can be found in foods containing carotene, such as carrots. Vitamin D is involved in the absorption of key minerals such as iron, calcium, and phosphate. It is usually obtained through sun exposure. Vitamin E is an antioxidant and is used to prevent the effects of reactive oxygen species (free radicals). Finally, Vitamin K is a clotting factor that is essential to repair and clot damaged endothelial walls and tissue.

Decreased levels of lipids will actually increase the absorption of these essential lipid vitamins. The body will try to absorb even the slightest amount of vitamins in diet to compensate for the depletion of these vitamins; therefore, the rate of absorption of Vitamin D will increase.

Phospholipids, as the name implies, require a phosphate head group attached to two fatty acid tails. Their polar phosphate head groups and non-polar fatty acid tails are perfect for a bi-layer membrane, where 2 layers of phospholipids are arranged such that their non-polar tails face each other and their polar phosphate head groups face outwards.

The correct answer is "sterols." The most common sterol in animals is cholesterol, which is an important structural component of cell membranes and the precursor to steroid hormones. Acetyl-CoA is not a lipid but is a precursor to cholesterol itself. The other answers are lipids with other functions. While phospholipids are an important part of cell membranes, they are not precursors to steroid hormones.

Glucose is a monosaccharide that is utilized for energy production in cells. Decrease in glucose levels in blood and tissues will lead to decreased production of energy (ATP) and, subsequently, will cause the person to be lethargic. Recall that glucose undergoes glycolysis to create products that will eventually undergo Krebs cycle and/or oxidative phosphorylation to generate ATP.

Glycogen is a storage molecule found typically in liver. It is made up of numerous glucose molecules bonded together by glycosidic bonds. If there is a decrease in blood glucose levels, liver initiates the breakdown of glycogen to individual glucose molecules and deposits these molecules in the blood; therefore, this patient’s liver will break down glycogen and create individual glucose molecules.

Fatty acid is another type of macromolecule used to synthesize energy. If there is a decrease in levels of glucose, fatty acids from adipose tissue and muscle will be mobilized and released into the blood. These fatty acids will now travel to tissues and supply energy (by generating ATP).

Carbohydrates are first lines of energy source for tissues. If there is a decrease in the amount of carbohydrates, then other energy sources such as fatty acids and proteins are mobilized and undergo metabolism to produce energy. One of the byproducts of fatty acid metabolism are ketone bodies; therefore, a decrease in carbohydrates will lead to an increase in fatty acid metabolism and, subsequently, an increase in ketone bodies.

Glycogen stores will be depleted because liver will respond to the decreased glucose levels and break down glycogen to component glucose molecules. Low carbohydrate concentration will decrease blood glucose levels.

Pyruvate carboxylase is an enzyme involved in gluconeogenesis, which is the generation of glucose from non-carbohydrate carbon substrates. This enzyme aids in the formation of PEP (phosphoenolpyruvate) from pyruvate. It converts pyruvate to oxaloacetate in the mitochondrion, requiring the hydrolysis of one molecule of ATP.

Proteins are the most diverse group of macromolecule. They can be fibrous (structural) or globular (receptors, enzymes, signaling molecules, and more).

Cysteine (C) is the only amino acid of the group to possess an uncharged R group at normal blood pH levels.

Arginine (R) and lysine (K) have positively charged R groups, and are considered basic. Aspartate (D) and glutamate (E) have negatively charged R groups, and are considered acidic.