Teaching #23 · For science teachers · A working draft, added to each year
Living Wet Mounts Without an Aquarium: Moss, Ivy, Onion and Pond Water From Your Own Yard
The short version
- A moss leaf does Elodea’s job. Most moss leaves are a single cell thick, so the chloroplasts are in plain view at 100× and 400×, and moss grows on almost every school campus in every season.
- Pond water, a jar of dead leaves and a cut ivy stem cover the rest: algae, live protists, stomata and guard cells, and the leaves for a floating leaf disk lab.
- Keep jars, not an aquarium. A clear jar on a windowsill needs no filter, no heater and almost no care.
- Say no to turtle and reptile tank water. Those animals carry Salmonella, and their tank water and plants carry it too.
- Never release a store-bought water plant. “Anacharis” is usually Egeria densa, an invasive species in Virginia.
Elodea is in every lab manual because its leaves are two cells thick and its chloroplasts stream around the cell. It is also hard to keep. Pet stores carry it some months and not others, it melts in a classroom tank over a long weekend, and the plant sold as “anacharis” is usually a different species that should never reach a stream. Every year the same scramble happens the week of the microscope lab.
The fix is to stop depending on one plant. What a microscope lab needs from a living specimen is a sheet of cells thin enough to see through, with something green inside. A yard, a pond edge and a kitchen supply that for free, and some of it is better than Elodea.
What to collect, and what each one shows
| Material | Where to find it | How to mount it | What students see | Good for |
|---|---|---|---|---|
| Moss leaf | Shady sidewalk edges, the north side of a building, tree bases, a lawn that stays damp. Carry it in a damp zip bag. | Pull one tiny leaf off a stem with forceps. Lay it flat in a drop of water and lower the cover slip edge first. | One layer of cells with walls and packed chloroplasts; often a thicker midrib down the center. Cells are small, so 400× is where it pays off. | Plant cell structure, chloroplasts, measuring cells against the field of view. The everyday replacement for Elodea. |
| Onion skin, in water and in iodine | The kitchen | Peel the thin, clear skin from the inside of a fleshy layer. One piece in water, one in iodine (Lugol’s) on a second slide. | Brick-shaped cells with walls; the nucleus jumps out in iodine and is faint in water. No chloroplasts, since the bulb grows underground. | Why a stain helps, and a controlled comparison where the stain is the only difference. |
| Ivy leaf, lower skin | English ivy on a fence or tree. Cut stems keep for weeks in a jar of water. | Bend the leaf and tear it at an angle so a thin, clear strip of the lower surface peels away. Mount that strip in water. | Stomata, each between two bean-shaped guard cells. The guard cells hold chloroplasts and the cells around them have few or none. | Gas exchange; a preview of the floating leaf disk lab, where the air spaces behind those stomata are what make the disks float. |
| Green “hair” algae | Strands on rocks under a waterfall, on a pond liner, or floating in a sunny corner. Slippery strands are often Spirogyra. | A few strands, spread out, in a drop of the pond water they came in. | Unbranched chains of cells. In Spirogyra, each cell holds a green chloroplast wound into a spiral ribbon. | Chloroplast shape; a multicellular chain built from identical cells; protist versus plant. |
| Pond-edge water and a little muck | The shallow edge of a pond, a birdbath, a rain barrel, a puddle that has stood for weeks. Take some of the brown film on the bottom. | A drop from the bottom of the jar, where the sediment settles. Scan at 40× and 100× first, since things move. | Live protists, diatoms, sometimes rotifers and small worms. Anything moving is worth stopping for. | Living versus prepared slides; diversity; prokaryote versus eukaryote when a cyanobacterium turns up. |
| Leaf infusion jar | Dead leaves or dry grass from the yard, in pond water or tap water that has stood a day. | A drop from the surface film, a drop from the side of the jar and a drop from the bottom. Each depth holds different organisms. | Bacteria in the first days, then a rise of ciliates such as Paramecium, then flagellates, amoebae and rotifers. | Succession and food webs in a jar; live protists on demand. |
| Water squeezed from soaked moss | The same moss as above, dried out, then soaked. | Soak a clump in rainwater or bottled water for a few hours to a day, squeeze it over a dish, and search the water under a dissecting scope. | Rotifers, nematodes and, with patience, tardigrades. | Animals that survive drying out; the scale of multicellular life next to single cells. |
| Elodea or Vallisneria, if you have them | A colleague’s fish tank, never a turtle tank (see safety below). A science supply house. | A young leaf from near the tip, flat in water. | The classic: cell walls, chloroplasts and cytoplasmic streaming, best after the leaf sits under a lamp for a while. | Streaming and living movement inside a cell. |
Pairings that teach something
One slide shows a cell. Two slides side by side make an argument. These pairs each answer a question students can state before they look.
| The question | Pair these | What settles it |
|---|---|---|
| What makes a plant cell different from an animal cell? | Moss leaf beside prepared human epithelium | The wall and the chloroplasts in one, neither in the other, at the same magnification |
| Why stain anything? | Onion in water beside onion in iodine | The nucleus that was there all along, made visible, with the stain as the only change |
| Do all plant cells photosynthesize? | Moss leaf beside onion skin, then the ivy peel | Green leaf cells, colorless bulb cells, and guard cells as the green exception in the leaf’s skin |
| How do gases get into a leaf? | Ivy peel, then the floating leaf disk lab with ivy leaves | Stomata on the slide; disks that sink when the air is pulled out and float as oxygen collects |
| Is a dead, stained cell the same as a living one? | Prepared Amoeba slide beside a live pond or infusion drop | Movement, feeding and contractile vacuoles that a prepared slide cannot show |
| Prokaryote or eukaryote? | A bacteria slide, a pond drop with a blue-green filament, and Spirogyra | The cyanobacterium makes food with no chloroplast and no nucleus; Spirogyra has both |
| How big is a cell, really? | Moss leaf cells and onion cells, each measured against the field of view | Two numbers in micrometers that differ by several times, from cells that look alike |
Safety calls
| Source | The risk | What to do |
|---|---|---|
| Turtle, frog or other reptile and amphibian tanks | These animals commonly carry Salmonella without looking sick, and it is in their water and on the plants in it. | Do not use them. Not the water, not the plants. Use a fish tank or a pond instead. |
| Pond and puddle water, infusion jars | Mixed bacteria, sometimes pathogens, especially near geese, livestock or runoff | Collect from clean-looking water away from animal waste. Gloves for handling, no mouth pipetting, cover cuts, wash hands after. Keep jars lidded loosely and dispose of cultures by your district’s procedure. |
| Iodine (Lugol’s) | Stains skin and clothes; irritating to eyes | Goggles and gloves for the iodine step; dropper bottles, not open beakers. |
| English ivy | Sap can irritate some people’s skin. English ivy is also on Virginia’s invasive list. | Gloves when cutting and peeling; wash hands. Bag the trimmings for the trash rather than the compost pile. |
| Store-bought water plants | “Anacharis” is usually Egeria densa, and hydrilla turns up as a hitchhiker. Both are on Virginia’s invasive plant list. | Never put them in a pond, a ditch or a drain. Dry them out and bag them for the trash. |
| Collecting outdoors | Rules on public land; allergies to mold and grass | Collect at home or on school grounds, a pinch at a time. A student with mold or grass allergies works with the onion and prepared slides. |
| Glass | Cut fingers from slides and cover slips | A glass box at every bench; broken glass is never picked up by hand. |
Keeping material going without an aquarium
An aquarium is a pet. It needs a filter, a heater, water changes and someone on holidays. The four setups below need a windowsill and a minute a week, and each one fails gently: if it dies, the yard still has more.
- The moss box. A clear plastic food container with a lid, a layer of soil, and a few clumps of moss pressed onto it. Mist it when the lid stops fogging. Bright, indirect light. It stays green for months and gives a leaf whenever a lab needs one.
- The pond jar. A clear quart jar, two-thirds pond water, a spoonful of the bottom sediment, a few strands of green algae and one dead leaf. Lid on loosely. Bright light but not direct sun, which cooks a jar. Top it up with rainwater or tap water that has stood a day. The community inside changes week to week, which is half the interest.
- The leaf infusion. A handful of dead leaves or dry grass, rinsed, in a jar of pond water or standing tap water. Loose lid, indirect light, and leave it alone. It turns cloudy and smells within a few days as bacteria bloom; the protists that eat them follow in about a week and peak over the next two or three. Start it two weeks before the lab day it serves. A commercial version of the method uses timothy hay and spring water, and yard leaves work on the same principle.
- The ivy jar. Cut ivy stems standing in water on the windowsill. They stay fresh for weeks and often root, which makes them a steady supply for leaf peels and for leaf disks.
When to do what
| Before the lab | Job |
|---|---|
| Two weeks | Start a leaf infusion if you want live protists in quantity. |
| A week | Count working microscopes and prepared slides; cut ivy stems into a jar of water. |
| One to three days | Collect moss into a damp bag and pond water into a lidded jar. Keep the jar out of the cold and out of a hot car. |
| The morning of | Make one test mount of each material and look at it yourself. Set the best one at the front scope. |
Who you are likely to meet in a drop of pond water
A first look at pond water is a crowd of moving shapes with no names. A handful of organisms turn up in most freshwater samples, and each one carries an idea from the course.
| Organism | How to recognize it | The idea it carries |
|---|---|---|
| Paramecium | A clear slipper shape covered in cilia, swimming fast in a spiral and backing up when it bumps something | One cell doing everything: feeding, moving, getting rid of water with contractile vacuoles |
| Vorticella | A bell on a thin stalk, anchored to debris; the stalk snaps into a coil and slowly stretches out again | A contractile protein system inside a single cell |
| Stentor | A large trumpet, often blue-green, sweeping food in with a ring of cilia | How big one cell can get, and why it carries a giant nucleus with many copies of its genome |
| Euglena | A green spindle with a red eyespot near the front, changing shape as it moves | A cell that both photosynthesizes and eats, which troubles the plant–animal split |
| Diatoms | Golden-brown boat or disk shapes with glassy, patterned walls, some gliding slowly | A cell wall made of silica; a large share of the oxygen made in water |
| Desmids such as Closterium | Bright green crescents or paired halves joined at a narrow waist | Symmetry and chloroplasts in a single cell |
| Spirogyra | Long unbranched green threads with a spiral chloroplast in each cell | Chloroplast shape, and a chain of identical cells |
| Cyanobacteria such as Oscillatoria | Blue-green filaments that glide and sway slowly, with no visible chloroplast or nucleus | A prokaryote that photosynthesizes; the ancestor of the chloroplast |
| Amoeba and relatives | A gray, shapeless blob near the bottom, flowing forward on pseudopods | Cytoskeleton and movement without cilia or flagella |
| Rotifers | Small, clear, many-celled animals with a spinning crown of cilia at the head | Multicellular animals smaller than some protists |
| Tardigrades | Plump, eight-legged and slow, clambering through moss debris | Animals that survive drying out by shutting down |
Tips at the scope
- Start low. Scan pond drops at 40× and 100×; a ciliate crosses the field at 400× before anyone can focus on it.
- Slow the swimmers. A few cotton fibers pulled from a ball under the cover slip make a maze that traps fast ciliates. A drop of a methyl cellulose slowing solution does the same.
- Turn the light down. Live, unstained cells are nearly transparent. Close the diaphragm until edges appear.
- Take from the bottom. Most of the life in a jar sits in the sediment and on the glass, not in the clear middle.
- Photograph it. A phone or an iPad held to the eyepiece turns a moving organism into evidence a student can label later.
Going further
- Journey to the Microcosmos (YouTube): short, beautifully filmed episodes on pond microbes, a good way for a teacher or student to learn names and behavior before looking.
- The Microbe Zoo: Spirogyra, Michigan State University’s Digital Learning Center for Microbial Ecology.
- Make a Hay Infusion, Carolina Biological: the classic culture method, with its succession of organisms.
- Tardigrades: how to find them and observe them, Microbehunter Microscopy.
- Study Photosynthesis with the Floating Leaf Disk Assay, Science Buddies, and Floating Leaf Disk, Brad Williamson’s write-up at the Cornell Institute for Biology Teachers. Ivy is one of the suggested leaves.
Sources, checked November 2026: Centers for Disease Control and Prevention, Tiny turtles, illegal to sell as pets, causing Salmonella illnesses again in young kids (August 2024) · U.S. Food and Drug Administration, Pet Turtles and Salmonella Lesson Plan · Virginia Department of Conservation and Recreation, Virginia Invasive Plant Species List (2024), which lists Egeria densa, Hydrilla verticillata and Hedera helix · Carolina Biological Supply, Make a Hay Infusion.