Correct Option: B. Liver Detailed Explanation: The liver is a vital organ in the body that plays a crucial role in regulating various metabolic processes, including the management of amino acids and glucose levels. Here’s a step-by-step breakdown of why the liver is the correct answer:

1. Role of the Liver in Metabolism:
2. The liver is responsible for the metabolism of carbohydrates, proteins, and fats. It helps maintain homeostasis by regulating the levels of glucose and amino acids in the bloodstream.
3. When you consume food, especially carbohydrates, the liver converts excess glucose into glycogen for storage. This process is called glycogenesis. When blood glucose levels drop, the liver can convert glycogen back into glucose through glycogenolysis.
4. Regulation of Amino Acids:
5. The liver also plays a key role in amino acid metabolism. It can convert excess amino acids into glucose through a process called gluconeogenesis, especially during fasting or low-carbohydrate intake.
6. Additionally, the liver is involved in the deamination of amino acids, which is the removal of the amino group. This process is essential for the production of urea, which is excreted by the kidneys.
7. Hormonal Regulation:
8. The liver responds to hormones such as insulin and glucagon. Insulin, released by the pancreas after eating, promotes the uptake of glucose by the liver and its conversion to glycogen. Conversely, glucagon stimulates the liver to release glucose into the bloodstream when blood sugar levels are low.
9. Storage and Release:
10. The liver acts as a storage site for various nutrients, including glucose (as glycogen) and amino acids. It releases these nutrients into the bloodstream as needed to maintain stable levels, ensuring that the body has a constant supply of energy and building blocks for proteins.

Why the Other Options Are Incorrect:

• A. Kidney:
• The kidneys primarily function in filtering blood, removing waste products, and regulating electrolyte balance and fluid levels. While they do play a role in amino acid reabsorption and glucose reabsorption, they do not regulate the overall levels of these substances in the body like the liver does.
• C. Pancreas:
• The pancreas produces hormones such as insulin and glucagon, which are crucial for regulating blood sugar levels. However, it does not directly regulate the levels of amino acids or glucose in the same way the liver does. The pancreas acts more as a signaling organ rather than a regulatory one for these nutrients.
• D. Spleen:
• The spleen is primarily involved in filtering blood, recycling iron from red blood cells, and playing a role in the immune response. It does not have a direct role in regulating amino acids or glucose levels in the body.

Summary of Key Points:

• The liver regulates glucose and amino acid levels through processes like glycogenesis, gluconeogenesis, and deamination.
• It responds to hormonal signals (insulin and glucagon) to maintain homeostasis.
• The kidneys and pancreas have important functions but do not directly regulate amino acids and glucose like the liver.
• The spleen is involved in blood filtration and immune response, not metabolic regulation.

This understanding of the liver's role in metabolism is crucial for grasping how the body maintains energy balance and nutrient levels.