Question

question 3 of 13 biological membranes are present in all cells, and they make up the endomembrane system of eukaryotic cells. they have many functions, including acting as barriers that selectively allow the transport of small molecules and ions into and out of the cell or organelle. a biological membrane is a bilayer that contains lipids with hydrophobic head groups oriented toward the solvent (extracellular fluid and cytosol) and hydrophilic tail groups pointing inward. hydrophilic head groups pointing inward and hydrophobic tail groups oriented toward the solvent (extracellular fluid and cytosol). hydrophilic head groups oriented toward the solvent (extracellular fluid and cytosol) and hydrophobic tail groups pointing inward.

Explanation:

To solve this, we recall the structure of biological membranes (phospholipid bilayer). Phospholipids have hydrophilic (water - attracting) head groups and hydrophobic (water - repelling) tail groups. In an aqueous environment (like extracellular fluid and cytosol), the hydrophilic heads face the water (solvent), and the hydrophobic tails face inward (away from water), forming the bilayer.

• The first option is wrong because heads should be hydrophilic, not hydrophobic, and tails hydrophobic (not hydrophilic).
• The second option is wrong as heads should face the solvent (outward) and tails inward (not the other way around).
• The third option correctly describes the orientation: hydrophilic heads toward the solvent (water - based extracellular fluid and cytosol) and hydrophobic tails pointing inward (away from water).

Answer:

C. hydrophilic head groups oriented toward the solvent (extracellular fluid and cytosol) and hydrophobic tail groups pointing inward. (Note: Assuming the third option is labeled as C; adjust the label based on the actual question's numbering if different, but the content is as above.)