**Core Concept**
Gluconeogenesis is a metabolic process that generates glucose from non-carbohydrate sources, such as amino acids, lactate, and glycerol. This process is crucial for maintaining blood glucose levels during fasting, starvation, or intense exercise.

**Why the Correct Answer is Right**
Gluconeogenesis occurs in the liver and kidneys, where enzymes such as pyruvate carboxylase, phosphoenolpyruvate carboxykinase (PEPCK), and glucose-6-phosphatase catalyze the conversion of these substrates into glucose. The process involves several key steps, including the conversion of pyruvate to oxaloacetate, oxaloacetate to phosphoenolpyruvate, and finally, phosphoenolpyruvate to glucose. This process is tightly regulated by hormones such as glucagon and epinephrine, which stimulate gluconeogenesis, and insulin, which inhibits it.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct substrates involved in gluconeogenesis. While gluconeogenesis can utilize various substrates, the key substrates include amino acids, lactate, and glycerol.
**Option B:** This option is incorrect because it does not mention the key enzymes involved in gluconeogenesis, such as pyruvate carboxylase and PEPCK. These enzymes are essential for the conversion of pyruvate to glucose.
**Option C:** This option is incorrect because it does not specify the correct tissues involved in gluconeogenesis. While the liver and kidneys are the primary sites of gluconeogenesis, other tissues such as the small intestine and brain can also contribute to glucose production.

**Clinical Pearl / High-Yield Fact**
Gluconeogenesis is a critical process for maintaining blood glucose levels during fasting or starvation. In patients with impaired gluconeogenesis, such as those with liver disease or diabetes, glucose levels can drop precipitously, leading to hypoglycemia.

**Correct Answer: D. Gluconeogenesis occurs in the liver and kidneys, where pyruvate carboxylase, PEPCK, and glucose-6-phosphatase catalyze the conversion of amino acids, lactate, and glycerol into glucose.**