Beta oxidation is the process by which fatty acid molecules are broken down in the mitochondria to produce acetyl-coA, which can then enter the citric acid (Krebs) cycle. The correct transition from reactant to product for beta oxidation is fatty acid to acetyl-CoA.

Fatty acids are stored as triacylglycerols in adipose tissue, while cholesterol is stored as cholesteryl esters in a number of different tissues. Both fatty acids and cholesterol are hydrophobic molecules, which is why they are stored as lipid droplets within their respective tissues. 

Both cortisol and aldosterone are synthesized in the adrenal cortex with cholesterol as the precursor. Mineralocorticoid refers aldosterone, which is also secreted by the adrenal cortex. All of these hormones are steroidal, which means they are derived from cholesterol. Other steroid hormones are the sex hormones.  

Gluconeogenesis, the process of creating new glucose from precursors, occurs in the liver and to a very small extent in the cortex of the kidney. The largest stores of glycogen are also located in the liver, but become quickly depleted in situations of low blood glucose.

Glycogen is the polymer form of glucose, stored in the liver and other tissues when glucose is abundant. When glucose levels are high, glucose-1-phosphate is assembled into branching chains of glycogen. When glucose levels fall, glycogen is broken down by glycogen phosphorylase back into glucose-1-phosphate units. These monomers can be used in glycolysis and cellular respiration. Glycogen is the first source of energy that is used when glucose stores are low.

Pyruvate can be converted to acetyl-CoA by decarboxylation. Beta oxidation can convert fatty acids to acetyl-CoA. Transaminases can be used to make alpha-keto acids, which can be converted to acetyl-coA. Glucose cannot be directly converted to acetyl-CoA; it must be transformed into pyruvate first.

Carbohydrates can be stored as glycogen in the liver, fats can be stored as triglycerides or fatty acids in adipose tissue, and proteins can be made into alpha-keto acids. Hence, all of these are forms of energy storage that can be used as alternative energy sources.

Cellulose is a polysaccharide that is found in plants. Humans cannot digest cellulose due to its beta-glycosidic linkages.

The three ketone bodies utilized by the body are acetoacetate, beta-hydroxybutyrate, and acetone. These are produced from acetyl-CoA during beta-oxidation. Acetyl-CoA undergoes conversion reactions to the three ketone bodies in the liver.

Even if you did not know the names of the ketone bodies, you should know that aldehyde is not a ketone because its carbonyl moiety does not have carbons connected from both sides to the carbonyl carbon.

The correct answer is arrow B. An amide group is a carbonyl group with a nitrogen that is in the alpha position (directly attached to the carbonyl carbon). Penicillin has two different amide groups in its chemical structure, but only one has an arrow pointing to it in the diagram. Arrow B points to a primary secondary amide, bond to one hydrogen and two carbons. The other amide in the molecule is a tertiary amide, bond to three carbons and no hydrogens.

Amides have a structure of a ketone group adjacent to an amine group.

In an amide bond, all of the atoms (the nitrogen, the carbonyl oxygen, and carbonyl carbon) are hybridized because of resonance; the lone pair on nitrogen can delocalize into the carbonyl pi bond. The amide bond is polar, mildly acidic, with a secondary amide having the structure shown. Finally, amides are often formed by a condensation reaction between a carboxylic acid and an amine, which produces water as a byproduct.