**Core Concept:** Glucose-6-phosphate is a key intermediate in glycolysis, the primary pathway for glucose utilization in tissues. In a well-fed state, the liver and muscles primarily undergo gluconeogenesis and glycogenesis, respectively, while the kidney filters glucose for excretion.

**Why the Correct Answer is Right:** In a well-fed state, glucose-6-phosphate is mainly converted into glycogen (stored glucose) in the liver through a process called glycogenesis. This process involves the enzyme glycogen synthase, which is activated under conditions of high glucose availability.

**Why Each Wrong Option is Incorrect:**

A. Option A (Gluconeogenesis) occurs when glucose levels in the body are low, not in a well-fed state.
B. Option B (Photosynthesis) is a process taking place in plants, not animals.
C. Option C (Gluconeogenesis) occurs in the liver when glucose levels are low, not in a well-fed state.
D. Option D (Gluconeogenesis) is a process taking place in the kidney to filter glucose for excretion, not in the liver or muscle.

**Clinical Pearl:** Understanding the correct answer helps in grasping how glucose homeostasis is maintained in the body, and appreciating the role of different organs in glucose disposal during well-fed states. This is crucial in postgraduate medical exams as it demonstrates knowledge of glucose homeostasis and the actions of various enzymes and organs in this process.