Ultrafiltration and Selective Reabsorption in the Nephron · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

How the nephron filters then reclaims

Science · The Human Body · ages 17-18
Name ______________________   Date ____________

  1. Which of these is too large to pass the filter?

    • Urea
    • Glucose
    • Plasma proteins

  2. Why is pressure in the glomerulus high enough to force filtration?

    • The exit arteriole is narrower than the entry one
    • The tubule squeezes the blood vessels tight
    • The capsule lining pumps fluid out actively

  3. Where is glucose normally reclaimed from the filtrate?

    • In the collecting duct by osmosis alone
    • In the glomerulus by high pressure
    • In the proximal tubule by carrier proteins

  4. Why does healthy urine contain no glucose?

    • Glucose is never filtered out at all
    • The tubule reabsorbs every filtered glucose molecule
    • Glucose is destroyed inside the capsule

  5. How do filtration and reabsorption differ as mechanisms?

    • Filtration uses pressure, reabsorption uses carriers
    • Filtration uses carriers, reabsorption uses pressure
    • Both steps use the same carrier proteins

  6. What powers glucose recovery in the proximal tubule?

    • Stronger blood flow through the kidney
    • Stretching of the capsule wall
    • Sodium co-transport riding a sodium gradient

  7. Glucose appears in urine when blood glucose overwhelms the tubule carriers.

    Circle one:   True   False

  8. A student says glucose stays in blood because the filter blocks it. What is wrong?

    • Glucose is filtered freely, then fully reabsorbed downstream
    • Glucose is too large to ever leave the blood
    • The filter uses carriers to hold glucose back
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Answer key

For grown-ups. Fold this page away before handing over the rest.

How the nephron filters then reclaims W1-mt_vSKfoJN6zh-s1

  1. Plasma proteins · Cells and plasma proteins are held back while small cargo crosses.
  2. The exit arteriole is narrower than the entry one · A wide entry and narrow exit pile blood up, so pressure climbs.
  3. In the proximal tubule by carrier proteins · Carriers in the proximal tubule pull every glucose molecule back into the blood.
  4. The tubule reabsorbs every filtered glucose molecule · All filtered glucose is reclaimed because normal levels sit below the carriers ceiling.
  5. Filtration uses pressure, reabsorption uses carriers · Filtration is pressure forcing fluid through membranes. Reabsorption is carriers winning cargo back.
  6. Sodium co-transport riding a sodium gradient · Sodium potassium pumps build a gradient and symporters ride it to pull glucose back.
  7. True · Carrier numbers are limited, so extreme blood glucose saturates them and the excess spills over.
  8. Glucose is filtered freely, then fully reabsorbed downstream · Glucose passes the filter easily. Its absence from urine is due to reabsorption, not blocking.
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