Gas Exchange: Lungs and Gills Online Microscope Lab

An online microscope lab for high school science on StudyScope. Students work through 4 real prepared microscope slides in order: Lung (top section) Slice 4, Lung (top section) Slice 3, Fish Gill (Cross Section), and Oyster Gill (Cross Section).

Students compare three gas exchange surfaces: the air sacs of a human lung, the thin plates of a fish gill, and the folded gill of an oyster. On each slide they describe the surface first, then check their ideas against labeled structures, and they use the ruler to measure how thin an alveolar wall and a gill lamella really are. The big idea: every gas exchange surface is thin, folded into a large area, and close to blood, because diffusion only works over short distances. You drive the slides; students follow on their own screens and can pan and zoom. Have students keep a table with four columns: "Organism," "Air or water," "Surface," and "Thickness I measured." About 35 minutes.

Grade level
High school
Time
35 minutes
Subject
Physiology & Organs
Slides
4
NGSS
HS-LS1-2

NGSS alignment

Lab steps

  1. Human lung: alveoli

    Slide: Lung (top section) Slice 4

    • This is a thin slice of human lung, stained pink and purple. Look at the whole piece before you zoom in. Describe the pattern. What does it remind you of? What do you think fills the white spaces in a living lung?
    • Zoom in here. The white spaces are air sacs called alveoli. The purple lines between them are the walls, and the dark dots in the walls are cell nuclei. Pick one wall and trace it with your eyes. How many cells thick does it look?
    • Check the labels. One alveolus is boxed, along with a stretch of its wall and one cell nucleus. Tiny blood vessels called capillaries run inside these walls, so the blood sits right next to the air. Sketch two or three alveoli and label the air space and the wall.
    • Measure it. Use the ruler tool to measure across the thinnest part of a wall, from the air on one side to the air on the other. The slide is calibrated, so the ruler reads in micrometers (1 micrometer is a thousandth of a millimeter). Record your number in your table. Then measure one alveolus from wall to wall. How many wall thicknesses would fit across it?
    • Oxygen moves from the air into the blood by diffusion, and diffusion is fast only over very short distances. What would happen to oxygen entering the blood if these walls were ten times thicker? Why does a lung have millions of tiny sacs instead of one big balloon?

  2. Human lung: blood vessels and soot

    Slide: Lung (top section) Slice 3

    • This is another slice of human lung. Find the thick, bright pink rings and the black specks near them. Compare the wall of the biggest pink ring with the alveolar walls around it. Which is thicker? Which one could oxygen cross easily?
    • Check the labels. The pink rings are arteries. Their thick, muscular walls carry blood toward the alveoli, but gases don't cross them. The black specks are carbon from smoke and polluted air that was breathed in. Why does it make sense for an artery wall to be thick while an alveolar wall is thin?
    • The soot got this far because every breath carries air, and anything in it, all the way to the alveoli. What could happen to gas exchange if the alveolar walls were coated or thickened by years of breathing smoke?

  3. Fish gill: filaments and lamellae

    Slide: Fish Gill (Cross Section)

    • Now a fish gill, cut so you can see it from the side. Look at the whole slide first. Describe the shape. What does it remind you of? How is it built differently from the lung?
    • Look at the long fingers sticking out from the thick pink band in the middle. Each finger has a stiff rod running up its center. Check the labels. The band is the gill arch, the fingers are gill filaments, and the rod is cartilage that keeps each filament from collapsing. Why would a gill need stiff support when the fish lives in water?
    • Zoom in on the side of a filament. Thin plates fan out from it like pages of a book. Describe one plate. How many cells thick is it? What do you see packed inside?
    • Check the labels. The plates are lamellae. Each one is two thin layers of cells with blood flowing between them. The small oval cells inside are red blood cells. Water flows over the lamellae, so oxygen only has to cross a few micrometers to reach the blood. Add the fish gill to your table. What does it use instead of alveoli?
    • Measure it. Use the ruler to measure the thickness of one lamella, from its top surface to its bottom surface. Record the number in your table. How does it compare with the alveolar wall you measured? Why might both surfaces end up within a few micrometers of each other?

  4. Oyster gill: breathing and feeding

    Slide: Oyster Gill (Cross Section)

    • This is a slice through the gill of an oyster. Look at the edges of the tissue first. Describe what you see along the edges. Where else today did you see a surface built from many small, repeating parts?
    • Check the labels. The knobs along the edge are gill filaments, lined up like the teeth of a comb. Water flows between them into the large open spaces inside, called water tubes. The round pink cells in the loose tissue are the oyster's blood cells. Follow the path of water from outside the gill into a water tube. What does it pass on the way?
    • Zoom in on one filament. Find the two dark, stiff rods inside it. In a living oyster, the outside of each filament is covered in cilia, tiny hairs that beat to pull water through the gill. Why might the filaments need rods to hold them open while water is pumped past them?
    • An oyster uses the same water current for two jobs: getting oxygen and catching food. Tiny bits of food stick to mucus on the filaments and get swept to its mouth. Add the oyster to your table. Why would a large, folded gill help with both jobs at once?
    • Finish your table. For the lung, the fish gill, and the oyster gill, fill in: • air or water • the surface where gases cross • how it stays thin • how it gets a large surface area Then write two or three sentences: what do all three surfaces have in common, and why does diffusion force them to be built that way?

Slides used in this lab

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