Good microscope experiments for high school students go beyond just looking. They ask a question, change one variable and measure something. Some of the most reliable ones are:
- Estimating cell sizes using the field of view
- Watching osmosis and plasmolysis in red onion cells
- Comparing stomata density on different leaves
- Counting cells in each stage of mitosis in an onion root tip
- Timing cytoplasmic streaming in Elodea at different temperatures
- Measuring yeast budding or viability
- Finding the bacteria in live yogurt at 1000x
- Tracking how organisms change in a hay infusion over time
- Comparing hairs and fibers forensics-style
- Viewing crystals and starch under polarized light
Each one is described below with a question to investigate and what to measure. If you’re looking for simpler, more casual ideas, see our fun microscope activities for beginners.
First: Measure Your Field of View
Most of these experiments involve measuring or counting per unit area, so start by working out the diameter of your field of view at each magnification.
- Place a clear plastic ruler with millimeter markings on the stage and focus on it at the lowest power (often 40x total).
- Count how many millimeters span the circle of light. Estimate fractions as best you can.
- Calculate the field of view at higher powers using the ratio of magnifications. The field of view shrinks in proportion as magnification rises.
For example, if the field is about 4.5 mm across at 40x, it will be about 1.8 mm at 100x (4.5 × 40/100) and about 0.45 mm, or 450 micrometers (µm), at 400x. Your microscope’s figures may differ, so measure your own. If your school has an eyepiece reticle and stage micrometer, those give more precise measurements.
Experiment Ideas
1. Estimate the Size of Cells
Question: How big are different types of cells?
Make wet mounts of onion epidermis, Elodea leaf and any prepared slides you have. At a known field of view, count roughly how many cells would fit across the diameter, then divide the field diameter by that number. Compare cell types, or compare your estimate with published values and discuss why they differ.
2. Osmosis and Plasmolysis in Onion Cells
Question: How does salt concentration affect plant cells?
Red onion epidermis works well because the colored cell contents are easy to see. Make a wet mount in plain water and observe. Then place a drop of salt solution at one edge of the coverslip and touch a piece of paper towel to the opposite edge to draw it under. Watch the colored contents pull away from the cell wall (plasmolysis).
To measure: prepare several salt concentrations, and after a fixed time, count the percentage of cells in a field that show plasmolysis. Then draw distilled water back under the coverslip and see whether the cells recover.
3. Stomata Density on Leaves
Question: Do leaves have more stomata on the top or bottom surface? Do sun and shade leaves differ?
Paint a small patch of clear nail polish on a leaf surface and let it dry. Press clear tape over it, peel the polish off and stick the tape onto a slide. The peel holds an impression of the leaf surface, including the stomata.
To measure: count stomata in several fields at 400x, average them, and divide by the field area (π × radius²) to get stomata per square millimeter. Compare upper vs. lower surfaces, different species or plants grown in different conditions. Work in a ventilated room when using nail polish.
4. Counting Stages of Mitosis
Question: Which stage of mitosis takes the longest?
Use prepared slides of onion (Allium) root tip. In the growing region near the tip, many cells are dividing at any one moment. At 400x, classify every cell in a field as interphase, prophase, metaphase, anaphase or telophase, and repeat over several fields.
Because cells in a root tip are dividing at different times, the proportion of cells in each stage roughly reflects how long that stage lasts relative to the whole cycle. Students usually find most cells are in interphase. Some schools prepare fresh root tip squashes, but this usually involves hydrochloric acid and should only be done as a teacher-led procedure.
5. Cytoplasmic Streaming and Temperature
Question: Does temperature affect how fast cytoplasm moves?
In healthy Elodea leaf cells, chloroplasts often circulate around the edge of the cell. Pick one chloroplast at 400x and time how long it takes to travel a known distance (estimated from your field of view measurement). Repeat with leaves kept for a while in cooler and warmer water (warm, not hot). Take several measurements at each temperature, as individual cells vary a lot.
6. Yeast Budding and Viability
Question: How do sugar concentration or temperature affect yeast?
Mix dried baker’s yeast into warm water with different amounts of sugar. After a set time, put a drop on a slide at 400x and count the percentage of cells that are budding.
For a viability test, add a drop of dilute methylene blue to the yeast suspension. Dead cells generally stain blue, while living cells tend to stay pale because they can break down the dye. Compare a normal sample with one your teacher has heat-treated. A hemocytometer, if available, lets you count cells per milliliter properly.
7. Bacteria in Yogurt at 1000x
Question: What bacteria are in live yogurt, and what shapes are they?
Bacteria are too small to see well at 400x, which makes this a good introduction to the oil immersion objective. Smear a very small amount of plain live yogurt, diluted with a drop of water, thinly across a slide, let it air-dry, then stain it with methylene blue, rinse gently and let it dry again. (Some procedures heat-fix the smear by passing it through a flame; do this only with supervision.) At 1000x under oil, look for rod-shaped cells and chains of round cells.
Our guide to using a 100x oil immersion objective covers the technique, and what a 1000x microscope can see explains what to expect at that magnification.
8. Pond Water or Hay Infusion Succession
Question: How does a microbial community change over time?
Put a handful of dry grass or hay in a jar of pond water or rainwater and leave it loosely covered somewhere out of direct sun. Sample a drop every day or two for a few weeks, scanning several fields at 100x and 400x. Record which types of organisms you see and roughly how common each is. Often the mix changes noticeably over the weeks as different organisms take over.
The jar will smell. Wash hands after handling it, and dispose of it as your teacher directs.
9. Forensic Hair and Fiber Comparison
Question: Can you match an unknown hair or fiber to its source?
Collect hairs from volunteers and pets, and threads from several fabrics. Mount each and record features at 100x and 400x: diameter, color, whether there’s a visible medulla (central core) and its pattern. For hair scale patterns, make a cast by pressing a hair into a thin layer of clear nail polish on a slide, letting it set slightly and lifting the hair out. Then give a classmate an “unknown” sample to identify.
10. Crystals Under Polarized Light
Question: Which materials change the polarization of light?
Place one sheet of polarizing film over the light source and another between the objective and your eye (for example, held over the eyepiece). Rotate one until the background goes dark. Now look at crystals grown by evaporating solutions of different substances, or at grains of potato starch in water. Some crystals light up in bright colors against the dark background, and starch grains often show a dark cross pattern. Compare which materials do this and which don’t.
Safety Notes
- Follow your school’s rules on stains, chemicals and biological samples. Some schools no longer allow cheek cell samples, and many restrict culturing microbes from the environment.
- Stains such as iodine and methylene blue mark skin and clothing. Wear gloves and eye protection if your lab requires them.
- Blades and glass: cut away from your fingers, and dispose of broken slides and coverslips in the designated container.
- Electrical safety: keep water and wet slides away from the microscope’s power cord and switch.
- Wash your hands after handling pond water, hay infusions or any living sample.
Writing It Up
A good microscope investigation report usually includes:
- The question and your prediction
- Your independent variable, what you measured and what you kept the same
- A data table with repeated counts or measurements and their averages
- Labeled drawings, each noting the magnification, ideally with an approximate scale bar from your field of view measurements
- A discussion of limitations, such as small sample sizes, difficulty classifying borderline cells, or uncertainty in your field of view measurements
Better data starts with a well-adjusted microscope. Our guide on how to use a microscope properly covers the basics, and if your school’s microscopes have a field diaphragm, setting up Köhler illumination can noticeably improve image quality for counting and measuring.