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Biology 20

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Excretion and movement

Ten questions of mixed difficulty, covering Excretion and movement. Print it, or work through it on screen — the answer key starts on its own page.

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Excretion and movement

Biology 20 · maddyhelps.com

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  1. The functional unit of the kidney is the

    1. a) alveolus
    2. b) glomerulus
    3. c) villus
    4. d) nephron

  2. Filtration at the glomerulus forces out of the blood

    1. a) everything, including blood cells
    2. b) water, glucose, salts and urea, but not proteins or blood cells
    3. c) only wastes
    4. d) only urea and water

  3. According to the sliding filament model, a muscle fibre shortens because

    1. a) the filaments dissolve and reform shorter
    2. b) actin filaments are pulled past myosin filaments, without either changing length
    3. c) actin and myosin filaments both contract
    4. d) water leaves the muscle cell

  4. The main role of the kidneys is to

    1. a) filter the blood, removing wastes and adjusting water and salt balance
    2. b) produce bile
    3. c) store urine
    4. d) break down proteins into amino acids

  5. The loop of Henle makes concentrated urine possible because it

    1. a) adds urea to the filtrate
    2. b) actively pumps water out of the filtrate
    3. c) creates a salt concentration gradient in the medulla that water can be drawn into
    4. d) filters the blood a second time

  6. Aldosterone acts on the nephron to

    1. a) increase glucose reabsorption
    2. b) increase sodium excretion
    3. c) reduce blood volume
    4. d) increase sodium reabsorption, with water following

  7. Urea is produced in the

    1. a) large intestine
    2. b) liver, from the breakdown of amino acids
    3. c) bladder
    4. d) kidney, from filtered blood

  8. Nearly all of the glucose in the filtrate is reabsorbed in the

    1. a) proximal tubule
    2. b) loop of Henle
    3. c) Bowman's capsule
    4. d) collecting duct

  9. ADH raises the amount of water reabsorbed by

    1. a) increasing the rate of filtration
    2. b) making the collecting duct more permeable to water
    3. c) adding sodium to the filtrate
    4. d) slowing the heart

  10. Filtrate moves through the nephron in the order

    1. a) collecting duct, loop of Henle, glomerulus, Bowman's capsule
    2. b) glomerulus, Bowman's capsule, proximal tubule, loop of Henle, distal tubule, collecting duct
    3. c) glomerulus, loop of Henle, Bowman's capsule, distal tubule
    4. d) Bowman's capsule, glomerulus, loop of Henle, proximal tubule, collecting duct

Answer key · Excretion and movement

Biology 20 · maddyhelps.com

  1. d) nephron — Each kidney holds about a million nephrons, and each one does the whole job in miniature: filter, reabsorb, secrete. The glomerulus is only the filtering part of a nephron.
  2. b) water, glucose, salts and urea, but not proteins or blood cells — Filtration is driven by pressure and sorted by size, so small molecules go through whether the body wants to lose them or not. That is why useful substances have to be reclaimed further along.
  3. b) actin filaments are pulled past myosin filaments, without either changing length — Myosin heads bind, pivot and release repeatedly, walking the actin inwards. The filaments keep their own length throughout — the overlap increases and the sarcomere gets shorter.
  4. a) filter the blood, removing wastes and adjusting water and salt balance — Excretion is only half the job — the kidney also decides how much water and salt to keep, which makes it the main regulator of blood volume and pressure.
  5. c) creates a salt concentration gradient in the medulla that water can be drawn into — Water is never pumped directly. The loop builds a salty medulla, and when the collecting duct passes through it under the influence of ADH, water leaves by osmosis. Mammals with long loops can make very concentrated urine.
  6. d) increase sodium reabsorption, with water following — Water follows salt by osmosis, so reclaiming sodium reclaims water and raises blood pressure. ADH and aldosterone both conserve water, but by different routes — one moves water directly and one moves salt.
  7. b) liver, from the breakdown of amino acids — Deamination in the liver produces ammonia, which is toxic, so the liver immediately converts it to the much safer urea. The kidney removes urea but does not make it.
  8. a) proximal tubule — Active transport in the proximal tubule reclaims essentially all of it. Glucose only appears in urine when blood levels are so high that these transporters are saturated — which is why it is a sign of diabetes.
  9. b) making the collecting duct more permeable to water — Anti-diuretic hormone is released when the blood is too concentrated, and it makes the final stretch of the nephron leaky to water so more is recovered. The result is less urine, and more concentrated urine.
  10. b) glomerulus, Bowman's capsule, proximal tubule, loop of Henle, distal tubule, collecting duct — Blood is filtered into the capsule first, and everything after that is adjustment. Knowing the order matters because each segment does a different job.