Filtrates in the Bowman's capsule contain vitamins because

Step 1: Analyze the question The question asks why vitamins are found in the glomerular filtrate in the Bowman's capsule.

Step 2: The concept: ultrafiltration Blood enters the glomerulus under high hydrostatic pressure. This forces water and small dissolved substances out of the capillaries into the Bowman's capsule. The basement membrane acts as a filter, so only substances with a low molecular weight pass through.

• Pass through (small molecules): water, glucose, amino acids, urea, mineral salts, vitamins (especially water-soluble ones)
• Stay in the blood (large molecules): red blood cells, white blood cells, platelets, plasma proteins

Step 3: Evaluate the options

• A. They have low molecular weight. Correct. Vitamins are small molecules, so they pass through the basement membrane during ultrafiltration.
• B. Most of them are fat soluble. Incorrect. Fat-soluble vitamins (A, D, E, K) are mostly carried bound to proteins, so they filter poorly. Many filtered vitamins are water-soluble (B and C).
• C. They cannot be reabsorbed into the blood. Incorrect. Many useful substances in the filtrate, such as glucose and amino acids, are reabsorbed in the proximal convoluted tubule. Reabsorption happens after filtration and does not explain why substances are in the filtrate.
• D. Little amount is required by the blood. Incorrect. How much the body needs has no effect on what passes through the filter. Filtration depends on size and pressure.

Step 4: Answer Vitamins are present in the filtrate because they are small enough to pass through the filtration barrier.

Exam tip: Filtration in the kidney depends on size, not on need. Remember: "Small passes, big stays." Later, the tubules reabsorb what the body needs.