Enzymes are all proteins, however there are some RNA molecules that have been found to catalyze reactions, but they are termed ribozymes, not enzymes. They speed up reactions by lowering the activation energy of a reaction and do not change the energy states of the reactants or products. 

Enzymes work by lowering the activation energy of a reaction, which can occur either by bringing reactants closer together or by destabilizing the transition state. They do not affect the equilibirum of the reaction, meaning they do not affect the amount of reactants or products. They simply increase the speed at which products can be formed by reducing the amount of energy needed to power the reaction.

A competitive inhibitor will temporarily bind to the active site on an enzyme. This forbids substrates from entering the enzyme's active site and stops the enzyme from catalyzing the reaction.

In contrast, non-competitive inhibitors will bind to other regions of the enzyme, outside of the active site, and cause the active site to change shape. This change then prevents substrates from binding.

Inhibitors are able to prevent maximum enzymatic rates in a variety of ways. Some inhibitors, like noncompetive inhibitors, are able to attach at a point on the enzyme and alter its conformation. Competitive inhibitors, however, bind directly at the active site, which prevents substrate from entering the enzyme.

Competitive inhibitors are the only inhibitor type to bind directly to the enzyme actve site.

An inhibitor binds to an enzyme and stops it from performing its normal function. It does not destroy the enzyme and does not change the amount present, but it decreases the amount of activity of that enzyme.

Most inhibitors work by binding to an enzyme so that the substrate cannot bind to the enzyme, and thus the function cannot take place.

Inhibitors generally affect functionality by interfering with the reaction without altering the amount of substrate or enzyme molecules.

The correct answer is competitive inhibiiton by Compound A. You can gather that because Compound A's inhibitory properties were negated, the reaction rate increased. As a result, competitive inhibition by Compound A takes place since the reaction rate increases as reactant concentration increases which occurs regardless of inhibitor presence (assuming enough enzymes are present). In contrast, the concentration of reactants would be irrelevant in the case of allosteric regulation either by Compound A or an unknown compound. Enzyme Breakdown would not result in an increase of the reaction rate. 

A noncompetitive inhibitor does not directly compete with the substrate binding to the substrate-binding site of an enzyme. The inhibitor instead binds to another site on the enzyme, which alters the enzyme's affinity for its substrate; therefore, adding more substrate would not cause a change in enzymatic activity.

Hemoglobin is a protein found in red blood cells. It has a high affinity to bind to oxygen, carbon dioxide, and carbon monoxide. In the lungs, where oxygen concentrations are high, hemoglobin will bind to oxygen molecules and carry them through the blood to deliver to the cells of the body. Oxygen can then be used by these cells to gain energy through oxidative phosphorylation and the electron transport chain, which require oxygen as an electron receptor.

Though hemoglobin can bind carbon dioxide, most carbon dioxide waste is dissolved in the blood in the form of bicarbonate and carbonic acid. Hemoglobin's high affinity for carbon monoxide means that, when the gas is present in excess, it can block the binding sites for oxygen. This is the reason for the toxicity associated with carbon monoxide poisoning.

Proteins have the most diverse functions in biological systems. Their remarkable diversity in function is due to their diversity in structure. Structural proteins, such as tubulin and collagen, have a fibrous structure that aids their function. Enzymes have active sites that allow them to bind specific molecules (substrates) and enact a conformational change to facilitate chemical reactions. Signaling proteins include several types of hormones, known as peptide hormones. Protein receptors are commonly found embedded in the cell membrane and contain active sites to bind substrates, hydrophilic regions to interact with the cell environment and extracellular space, and hydrophobic regions to interact within the lipid bilayer.