Humber Admissions Practice Test

What is the main characteristic of phospholipids in biological membranes?

1. A polar, hydrophilic head and a nonpolar, hydrophobic tail

2. Only hydrophilic properties

3. A nonpolar head and a polar tail structure

4. Insoluble in water

The correct answer is: A polar, hydrophilic head and a nonpolar, hydrophobic tail

Phospholipids are essential components of biological membranes, and their unique structure is key to their role. They consist of a polar, hydrophilic (water-attracting) head and two nonpolar, hydrophobic (water-repelling) tails. This amphipathic nature allows them to form bilayers, which are the fundamental building blocks of cell membranes. In aqueous environments, the hydrophilic heads face outward towards the water, while the hydrophobic tails are oriented inward, away from the water. This arrangement creates a semi-permeable barrier that is crucial for maintaining the integrity of cells and facilitating the selective transport of substances. The other options do not accurately describe the structure of phospholipids. Only considering hydrophilic properties neglects the necessary hydrophobic aspects that are vital for membrane formation. Describing phospholipids as having a nonpolar head goes against the fundamental chemical properties that define them, as the head is indeed polar. Having a statement indicating that they are insoluble in water is misleading, since while the tails are hydrophobic, the heads are soluble or interact favorably with water. Thus, the option that accurately captures the dual nature of phospholipids and their functionality in biological membranes is