Cell transport—active transport across biological membranes In cellular physiology, which membrane component carries out active transport by moving solutes against their electrochemical gradients using metabolic energy?

Introduction / Context:
Active transport is a cornerstone concept in cell biology and biochemistry. It explains how cells accumulate nutrients, exclude toxins, regulate ion homeostasis, and maintain membrane potentials. Unlike passive processes, active transport requires energy and specific membrane machinery.

Given Data / Assumptions:

• Active transport moves solutes against their electrochemical gradient.
• Energy sources include ATP hydrolysis or coupling to existing ion gradients.
• Membranes contain lipids, proteins, and carbohydrates with distinct roles.

Concept / Approach:
The fluid mosaic model states that the lipid bilayer provides a hydrophobic barrier, whereas proteins carry out most selective and energy-dependent transport. Pumps and transporters are integral (transmembrane) proteins that span the bilayer and provide a pathway for ions and metabolites through conformational cycles powered by ATP or ion gradients.

Step-by-Step Solution:
Identify what defines active transport: movement against gradient with energy input.Match this function to the membrane component capable of catalyzing conformational cycles: integral proteins (for example, Na+/K+-ATPase, Ca2+-ATPase, H+-ATPase, ABC transporters).Exclude membrane constituents lacking catalytic transport function (cholesterol, carbohydrates, freely diffusing solutes).Therefore, the component responsible is integral (transmembrane) proteins.

Verification / Alternative check:
Pharmacologic inhibition of specific pumps (for example, ouabain on Na+/K+-ATPase) collapses gradients, confirming that proteinaceous pumps—not lipids or glycans—perform active transport.

Why Other Options Are Wrong:

• Cholesterol molecules: Modulate fluidity and permeability; they are not enzymes and do not move solutes uphill.
• Carbohydrates: Serve in recognition and protection; they lack transport activity.
• Hydrophobic molecules: May passively diffuse; diffusion is not active transport.
• Peripheral proteins: Do not span the bilayer; they generally cannot catalyze translocation across the membrane.

Common Pitfalls:
Equating any movement across membranes with “active” transport; forgetting that “active” requires energy and a protein pathway.

Final Answer:
Integral (transmembrane) proteins.