How Diffusion Works · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

How Diffusion Works

Science · Organisms & Life Processes · ages 12-13
Name ______________________   Date ____________

  1. Diffusion needs the cell to use energy to push particles around.

    Circle one:   True   False

  2. What is diffusion?

    • Net movement of particles from crowded to spread out
    • Particles moving from low concentration to high concentration
    • Particles staying still until something stirs them

  3. In the alveoli, oxygen moves from the air into the blood. Why?

    • Oxygen concentration is higher in the blood than in the air
    • Oxygen concentration is higher in the air than in the blood
    • The lungs use muscles to pump oxygen into the blood

  4. The doodle shows dots in two spaces linked by a membrane. How many more dots are on the crowded side than the empty side?

    >

    Answer: ______________

  5. Blood reaching the alveoli is high in carbon dioxide, and the air there is low in carbon dioxide. Which way does carbon dioxide diffuse?

    • From the air into the blood
    • It stays in the blood because gases cannot diffuse out
    • From the blood into the air

  6. A muscle cell is using up glucose fast, so its glucose concentration is lower than the blood next to it. How does the cell get more glucose?

    • Glucose moves from blood high to cell low
    • The cell pumps water out to pull glucose in
    • Glucose moves from the cell into the blood

  7. Lungs contain millions of tiny alveoli instead of one large sac. How does this help gas diffusion?

    • It lowers the concentration gradient between air and blood
    • It makes the distance for gases to travel longer
    • It gives a bigger surface area for gases to cross

  8. Lin says a thicker cell membrane makes diffusion happen faster because there is more material to move through. What is wrong with Lin's idea?

    • Lin is right, thicker membranes speed up diffusion
    • A thicker membrane means a longer distance, which slows diffusion
    • Membrane thickness has no effect on diffusion at all
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Answer key

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

How Diffusion Works W1-mt_i80I-1MLP2-s1

  1. False · Diffusion is passive. Particles move on their own because of their constant random motion, no energy from the cell is needed.
  2. Net movement of particles from crowded to spread out · Diffusion is the net movement of particles from high concentration to low concentration, caused by their constant random motion.
  3. Oxygen concentration is higher in the air than in the blood · Air breathed into the alveoli has more oxygen than the blood arriving there, so oxygen diffuses from air into blood.
  4. 6 · 8 minus 2 is 6. A bigger difference like this is a steeper concentration gradient, which makes diffusion happen faster.
  5. From the blood into the air · Carbon dioxide moves from where it is more concentrated, the blood, to where it is less concentrated, the air, the opposite direction to oxygen.
  6. Glucose moves from blood high to cell low · Glucose moves from where it is more concentrated to where it is less concentrated, with the help of a protein carrier in the cell membrane.
  7. It gives a bigger surface area for gases to cross · More alveoli means more surface area for gas exchange, and a larger surface area speeds up the total rate of diffusion.
  8. A thicker membrane means a longer distance, which slows diffusion · A shorter distance lets particles reach the other side sooner, so a thinner membrane speeds up diffusion, not a thicker one.
Worksheet · LightMySky