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Biology 20

Biology 20 · Worksheets

Final exam challenge

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

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Final exam challenge

Biology 20 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. The biosphere is

    1. a) all the water on Earth
    2. b) the layer of gases surrounding Earth
    3. c) the zone of Earth where living things are found
    4. d) the solid outer layer of Earth

  2. Aerobic respiration of one glucose molecule yields about

    1. a) 36 to 38 ATP
    2. b) 100 ATP
    3. c) 4 ATP
    4. d) 2 ATP

  3. Villi increase the efficiency of the small intestine by

    1. a) secreting acid
    2. b) greatly increasing its surface area for absorption
    3. c) pushing food along by peristalsis
    4. d) producing digestive enzymes

  4. The Krebs cycle takes place in the mitochondrial matrix and

    1. a) consumes oxygen directly
    2. b) produces most of the cell's ATP directly
    3. c) converts pyruvate back into glucose
    4. d) releases CO₂ while loading NADH and FADH₂ with electrons

  5. Denitrification differs from the other steps of the nitrogen cycle because it

    1. a) returns nitrogen to the atmosphere as N₂ gas
    2. b) fixes nitrogen into ammonia
    3. c) converts ammonium into nitrite
    4. d) releases ammonia from dead tissue

  6. Of these, the density-dependent limiting factor is

    1. a) disease spreading through a crowded population
    2. b) an early frost
    3. c) a forest fire
    4. d) a drought

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

    1. a) filters the blood a second time
    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) adds urea to the filtrate

  8. Peristalsis is

    1. a) waves of smooth muscle contraction that push food along the tract
    2. b) the reflex that closes the epiglottis
    3. c) the mixing of food with enzymes in the stomach
    4. d) the absorption of nutrients into the blood

  9. Most of the ATP from aerobic respiration is produced in the

    1. a) mitochondrion
    2. b) nucleus
    3. c) chloroplast
    4. d) cytoplasm

  10. Glycolysis converts one glucose molecule into

    1. a) one pyruvate and 2 NADH
    2. b) six CO₂ and 2 ATP
    3. c) two pyruvate, with a net gain of 4 ATP
    4. d) two pyruvate, with a net gain of 2 ATP and 2 NADH

Answer key · Final exam challenge

Biology 20 · maddyhelps.com

  1. c) the zone of Earth where living things are found — The biosphere is the thin shell where the atmosphere, hydrosphere and lithosphere overlap enough to support life. It is defined by the presence of life, not by a particular substance.
  2. a) 36 to 38 ATP — Roughly 2 from glycolysis, 2 from the Krebs cycle and the rest from the electron transport chain. The number is given as a range because the yield depends on how the cytoplasmic NADH is shuttled in.
  3. b) greatly increasing its surface area for absorption — Each villus carries microvilli, and the folding multiplies the area by a factor of hundreds. A structure that maximizes surface area for exchange shows up again in the lungs and the kidney.
  4. d) releases CO₂ while loading NADH and FADH₂ with electrons — The carbon dioxide you breathe out comes from here. The cycle makes very little ATP itself; its real product is the loaded electron carriers that feed the next stage.
  5. a) returns nitrogen to the atmosphere as N₂ gas — Nitrification, fixation and ammonification all keep nitrogen inside the ecosystem in usable forms. Denitrifying bacteria, working in oxygen-poor soils, remove it — which is why waterlogged soils lose fertility.
  6. a) disease spreading through a crowded population — Disease spreads faster the more closely packed the population is, so its effect depends on density. A fire or a frost kills much the same proportion whether the population is dense or sparse.
  7. 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.
  8. a) waves of smooth muscle contraction that push food along the tract — The muscle behind the food contracts and the muscle ahead relaxes, moving the bolus onward. It does not rely on gravity, which is why swallowing works upside down.
  9. a) mitochondrion — Glycolysis happens in the cytoplasm and yields a small amount, but the Krebs cycle and electron transport chain are both in the mitochondrion and produce the great majority.
  10. d) two pyruvate, with a net gain of 2 ATP and 2 NADH — Four ATP are made but two were invested at the start, so the net gain is two. The 2 NADH matter as much as the ATP, because they carry electrons to the chain later.