**Core Concept**
Competitive inhibition is a type of enzyme inhibition where the inhibitor molecule structurally resembles the substrate, competing with it for binding to the active site of the enzyme. This results in a decrease in the enzyme's catalytic activity, as the inhibitor occupies the binding site, preventing the substrate from accessing it.

**Why the Correct Answer is Right**
In competitive inhibition, the substrate and inhibitor have similar chemical structures, allowing them to compete for binding to the active site of the enzyme. This competition increases the substrate concentration required to achieve a half-maximal rate of reaction, a phenomenon known as the **Michaelis constant (Km)**. The enzyme's maximal velocity (Vmax) remains unchanged, as the inhibitor does not alter the enzyme's catalytic activity, but rather its ability to access the substrate.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to competitive inhibition, as it does not describe the mechanism of enzyme inhibition.
**Option B:** Non-competitive inhibition, on the other hand, involves the inhibitor binding to an allosteric site, altering the enzyme's conformation and reducing its activity, regardless of substrate concentration.
**Option C:** Uncompetitive inhibition is a type of inhibition where the inhibitor binds to the enzyme-substrate complex, reducing the enzyme's activity and Km.
**Option D:** Irreversible inhibition involves the covalent binding of the inhibitor to the enzyme, permanently inactivating it, and is not related to substrate affinity.

**Clinical Pearl / High-Yield Fact**
Remember that competitive inhibitors can be overcome by increasing the substrate concentration, as the inhibitor is outcompeted for binding to the active site.

**Correct Answer: D. Uncompetitive inhibition is a type of inhibition where the inhibitor binds to the enzyme-substrate complex, reducing the enzyme's activity and Km.**