True statement about fatty acid:
**Core Concept**
Fatty acids play a crucial role in various biological processes, including energy production, membrane structure, and signaling pathways. The classification of fatty acids into saturated, monounsaturated, polyunsaturated, and trans fatty acids is essential for understanding their functions and effects on human health.
**Why the Correct Answer is Right**
The correct answer is D. All, as each of the statements is true. Polyunsaturated fatty acids (PUFAs) are essential for membrane structure and are a crucial component of phospholipids, which make up cell membranes. Arachidonic acid, a polyunsaturated omega-6 fatty acid, is essential for various physiological processes, including inflammation and immune response. Hydrogenated vegetable oils contain trans fatty acids, which are formed during the hydrogenation process and are known to have adverse effects on cardiovascular health.
**Why Each Wrong Option is Incorrect**
**Option A:** While polyunsaturated fatty acids are essential for membrane structure, not all polyunsaturated fatty acids are essential for life. Some polyunsaturated fatty acids can be synthesized in the body, making them non-essential.
**Option B:** Although arachidonic acid is biologically important, it is not essential to life in the classical sense. Humans can synthesize arachidonic acid from linoleic acid, making it a conditionally essential fatty acid.
**Option C:** This statement is partially incorrect. Hydrogenated vegetable oils may contain trans fatty acids, but not all trans fatty acids are found in these oils. Some trans fatty acids occur naturally in meat and dairy products.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that trans fatty acids are formed during the hydrogenation process, which alters the chemical structure of unsaturated fatty acids, making them more solid at room temperature. This process is used to extend the shelf life of vegetable oils, but it also increases the risk of cardiovascular disease.
**✓ Correct Answer: D. All. All the statements are true.**