**Question:** Absorption of glucose is intestine is by

A. Passive diffusion
B. Active transport
C. Sodium-glucose co-transporter
D. Simple diffusion

**Correct Answer:** B. Active transport

**Core Concept:** Glucose absorption in the intestine is a crucial process for maintaining blood glucose levels and overall carbohydrate homeostasis. Glucose is absorbed passively through simple diffusion in the small intestine, specifically in the villi and microvilli of the enterocytes (intestinal epithelial cells).

**Why the Correct Answer is Right:** Active transport is a specific type of secondary active transport mechanism that plays a significant role in glucose absorption. In the small intestine, glucose is actively transported through the brush border membrane of the enterocytes using energy provided by the sodium-potassium pump (Na+/K+-ATPase). This active transport ensures an efficient and regulated absorption of glucose despite its low concentration gradient across the intestinal wall.

**Why Each Wrong Option is Incorrect:**

A. Passive diffusion (Option A) is a passive transport process that relies on concentration gradients and does not require energy input. While glucose can diffuse passively through the intestinal wall, active transport is essential for efficient and regulated absorption.

B. Simple diffusion (Option D) is a passive transport process that occurs when there is a concentration gradient, but it requires no energy input. In this context, active transport is necessary for glucose absorption due to the low glucose concentration gradient across the intestinal wall.

C. Sodium-glucose co-transporter (Option C) refers to a specific glucose transporter protein, SGLT1, which facilitates glucose uptake. While SGLT1 plays a role in glucose absorption, active transport, specifically through the use of energy, is the primary mechanism for efficient glucose absorption across the intestinal wall.

**Clinical Pearl:** Understanding the difference between passive and active transport is crucial for understanding the physiological mechanisms behind nutrient absorption, as well as medication absorption and distribution. Active transport ensures efficient and regulated absorption of essential nutrients like glucose, while passive transport relies on concentration gradients.