Antigens in cell membranes are glycoproteins and glycolipids

Steps:

• Identify antigens as surface molecules triggering immune responses, typically glycoproteins and glycolipids with carbohydrate chains.
• Label 1 as glycoprotein (protein with attached sugars) and 2 as glycolipid (lipid with sugars) in the diagram.
• Label 3 as phospholipid (basic membrane lipid without antigenic sugars) and 4 as cholesterol (structural component, not antigenic).
• Select components with sugar chains: 1 and 2.

Why A is correct:

• Antigens are defined as glycoproteins and glycolipids bearing unique carbohydrate markers for immune cell recognition.

Why the others are wrong:

• B includes 3, a phospholipid lacking antigenic carbohydrates.
• C includes 3, which is structural but not immunogenic.
• D includes 4, cholesterol that stabilizes membranes without triggering immunity.

Final answer: A