Which of the following is filtered from blood but not normally found in urine?

• A. Water
• B. Red blood cells
• C. H⁺
• D. Urea
• E. Amino acids

Answer: (E)

Verified step by step guidance

1. Understand the process of filtration in the kidneys: Blood is filtered in the glomerulus, where small molecules and water pass into the nephron, forming the filtrate.
2. Identify what is typically filtered: Substances like water, ions (e.g., H+), small molecules (e.g., urea), and nutrients (e.g., amino acids) are filtered from the blood.
3. Recognize what is reabsorbed: The nephron reabsorbs essential nutrients and molecules, such as amino acids, back into the bloodstream to prevent their loss in urine.
4. Consider what is not reabsorbed: Substances like urea are not fully reabsorbed and are excreted in urine, while amino acids are reabsorbed almost completely.
5. Conclude that amino acids, although filtered, are not normally found in urine because they are reabsorbed back into the blood, unlike substances like urea.