F. Plants: Anatomy, Growth, and Function · Plants: Anatomy, Growth, and FunctionObserving and Drawing Plant Tissues with a Microscope
F2.3 F2.1 A1.2 A1.4 A1.6 A1.12 A1.13About 70 minutes
Learning goals- I can choose suitable specimens and slides to observe the specialized tissues of roots, stems and leaves.
- I can use a compound light microscope safely and estimate the size of cells using the field of view.
- I can make a plan diagram and a cell drawing that follow the rules of scientific drawing.
- I can calculate the magnification of a drawing and add a scale bar.
Words to know
total magnification
Eyepiece (ocular) magnification × objective lens magnification.
field of view (FOV)
The circle of the specimen you can see through the microscope; its diameter gets smaller as magnification increases.
wet mount
A slide made by placing a specimen in a drop of water under a cover slip.
cross-section / longitudinal section
A cross-section is a thin slice cut straight across an organ; a longitudinal section is cut along its length.
stain
A dye that makes certain structures easier to see, for example iodine for starch.
plan diagram
A low-power drawing that shows the outlines and positions of tissues, without drawing individual cells.
drawing magnification
How many times larger a drawing is than the real object: drawing size ÷ actual size.
scale bar
A line on a drawing or image labelled with the real length it represents.
The first cells ever named were plant cells
In this unit you have seen many diagrams of roots, stems and leaves. Now you become the one making the observations. Botanists still learn plant anatomy the same way students did a century ago: thin slices, a microscope, a sharp pencil and careful drawing. Drawing forces you to look: you can't draw what you haven't noticed.
The curriculum asks you to identify and draw the specialized tissues of roots, stems and leaves (such as xylem and phloem) using a microscope and models. This lesson gives you the method; the activity gives you options with or without a microscope.
Remember from Grade 10
In Grade 10 you learned the parts of a compound light microscope, how to calculate total magnification (eyepiece × objective, for example 10× × 40× = 400×), and that the field of view shrinks as magnification increases: if you multiply magnification by 4, the field diameter is divided by 4. Here you use these skills to measure cells and draw plant tissues.
Choosing what to look at
To see a tissue clearly, you need a slice thin enough for light to pass through, usually only one or two cells thick. In a school lab you will mostly use prepared slides (thin, stained, permanent sections made by suppliers) and wet mounts of thin living specimens. The table lists good choices.
| Specimen | Type | What it shows |
|---|
| Buttercup (Ranunculus) root, prepared slide | cross-section | Dicot root: epidermis, wide cortex with starch grains, endodermis, X-shaped xylem |
| Corn (Zea mays) stem, prepared slide | cross-section | Monocot stem: scattered vascular bundles |
| Sunflower (Helianthus) stem, prepared slide | cross-section | Dicot stem: ring of bundles, cambium, pith |
| Lilac (Syringa) leaf, prepared slide | cross-section | Palisade and spongy mesophyll, veins, stomata |
| Elodea (pondweed) leaf, wet mount | whole leaf | Living cells with chloroplasts; sometimes cytoplasm visibly streaming |
| Nail-polish peel of a leaf's lower surface | surface view | Stomata and guard cells |
| Thin slice of potato with iodine (in a lab) | section | Parenchyma cells full of starch grains stained blue-black |
| Pear flesh, squashed | wet mount | Clusters of stone cells (sclerenchyma) that make pears gritty |
Working safely (A1.4)
- Carry a microscope with two hands: one on the arm, one under the base.
- Start on the lowest-power objective. Use the coarse focus only on low power; on high power use only the fine focus, so the lens doesn't crack the slide.
- Handle slides and cover slips by the edges; report broken glass and clean it up with a brush and dustpan, never bare hands.
- Never point a microscope mirror at direct sunlight: it can seriously damage your eyes.
- In a lab, stains such as iodine can irritate skin and eyes and stain clothes. Wear safety goggles and gloves, and check the WHMIS label and Safety Data Sheet. Cutting sections uses razor blades or scalpels, which should be handled only as your teacher directs. At home, a grown-up does any cutting with a kitchen knife.
Measuring cells with the field of view
Once you know the diameter of the field of view, you can estimate the size of a cell by counting how many fit across it:
cell size ≈ field diameter ÷ number of cells across
To find the field diameter at high power from the diameter at low power:
high-power diameter = low-power diameter × (low magnification ÷ high magnification)
Cell sizes are usually given in micrometres (µm): 1 mm = 1000 µm.
Rules of scientific drawing (A1.12)
- Use a sharp pencil and unlined paper. Make the drawing large: about half a page.
- Draw only what you see, not what a textbook shows.
- Use clear, continuous lines. No shading or colouring. If you must show darker or denser areas, use stippling (dots).
- Label with straight, ruled lines that do not cross each other. Put labels on one side (usually the right), lined up neatly, and write them horizontally.
- Add a title (specimen and view, e.g. "Cross-section of a buttercup root"), the magnification you observed at, and the drawing magnification or a scale bar.
Two kinds of drawings:
- A plan diagram (low power) shows the outlines of tissues and where they are, with no individual cells. It is often drawn as a sector (wedge) of a round cross-section, since the rest repeats.
- A cell drawing (high power) shows a few representative cells of one tissue in accurate detail: cell walls, nuclei, chloroplasts, and so on.
Drawing magnification and scale bars
Your drawing is usually much bigger than the real specimen. To report how much bigger:
drawing magnification = size on drawing ÷ actual size (both in the same units)
A scale bar is a short line on your drawing labelled with the real length it represents. Scale bars stay correct even if the drawing is enlarged or shrunk on a photocopier, which is why scientists prefer them.
To make a scale bar: decide what real length you want it to show (for example, 50 µm), then multiply by your drawing magnification to find how long to draw it.
Worked exampleLet's measure parenchyma cells
Under the 10× objective (with a 10× eyepiece), the field of view is 1.8 mm across. A student switches to the 40× objective and counts about 3 cortex cells across the field in a buttercup root. Estimate the cell diameter in µm.
- Low-power magnification = 10 × 10 = 100×. High-power magnification = 10 × 40 = 400×.
- High-power field diameter = 1.8 mm × (100 ÷ 400) = 0.45 mm.
- Cell diameter ≈ 0.45 mm ÷ 3 = 0.15 mm.
- Convert: 0.15 mm × 1000 µm/mm = 150 µm.
- This is an estimate: cells vary in size, and counting partial cells adds uncertainty. Counting in several fields and averaging improves it.
Each cortex cell is about 150 µm (0.15 mm) across.
Worked exampleLet's add a scale bar
The student draws one of those 150 µm cells as 45 mm wide. (a) What is the drawing magnification? (b) How long should a scale bar representing 50 µm be?
- (a) Convert to the same units: 150 µm = 0.150 mm.
- Drawing magnification = 45 mm ÷ 0.150 mm = 300×.
- (b) Scale bar length = real length × magnification = 50 µm × 300 = 15 000 µm = 15 mm.
- Draw a 15 mm line near the drawing and label it "50 µm".
(a) 300×; (b) a 15 mm line labelled 50 µm.
Just for funThe word cell was first used for a plant tissue. In 1665, Robert Hooke looked at thin slices of cork (dead bark cells) and thought the tiny boxes looked like the small rooms, called cells, where monks lived. So the first cells ever named were empty plant cells.
Hands-on activityDraw plant tissues: microscope or home version
With a microscope (school, library or a borrowed student microscope): prepare an Elodea leaf or onion epidermis wet mount, or use prepared slides. Make one plan diagram at low power and one cell drawing at high power, following all five drawing rules. Estimate cell size using the field of view.
Home version, no microscope: you need a celery stalk, a ripe tomato or pear, a magnifying glass or a phone camera on maximum zoom, a ruler and a pencil. A grown-up should do all cutting.
- Ask a grown-up to cut a very thin slice across a celery stalk. Hold it up to a window. Find the vascular bundles (the ring of small dots near the curved side) and the collenchyma strings at the ridges. Make a plan diagram of the slice: outline, epidermis, bundles, ground tissue. Measure the real width with a ruler and calculate your drawing magnification.
- Squash a tiny bit of ripe tomato or pear flesh on a clear plate. With the magnifier, tomato pulp shows individual large cells like tiny glistening beads; pear flesh shows hard, gritty clusters of stone cells. Draw a few.
- Model option: build a 3-D model of a dicot stem cross-section with modelling clay (or a paper-plate diagram), showing the epidermis, cortex, ring of bundles (phloem outside, xylem inside) and pith. Label it with flags made from tape and toothpicks.
What to look for: clean lines, no shading, ruled labels on the right, a title and a magnification or scale bar. Your celery plan diagram should show about 6 to 12 bundles in a curved row near the outer surface. Wash hands after handling food and compost the scraps.
Your turn
1What is the total magnification with a 10× eyepiece and a 40× objective?
2The field of view at 40× is 4.5 mm. What is it at 400×?
4.5 mm × (40 ÷ 400) = 0.45 mm.
3At 400×, 5 palisade cells fit across a 0.45 mm field. Estimate the length of one cell in µm.
0.45 mm ÷ 5 = 0.090 mm = 90 µm.
4Name three rules of scientific drawing.
Any three: use pencil; draw large; draw only what you see; continuous lines with no shading (stippling only); ruled, non-crossing label lines; labels on one side, horizontal; title, magnification or scale bar.
5What is the difference between a plan diagram and a cell drawing?
A plan diagram (low power) shows only the outlines and positions of tissues. A cell drawing (high power) shows a few individual cells in detail.
6Which prepared slide would you choose to see scattered vascular bundles?
A cross-section of a monocot stem, such as corn (Zea mays).
7Why should you never use the coarse focus knob on high power?
The high-power objective sits very close to the slide; the coarse knob moves the stage a lot, so the lens could hit and crack the slide or be damaged.
More practice: warm-up
1How many micrometres are in 1 mm?
2Write the formula for drawing magnification.
Drawing magnification = size on drawing ÷ actual size (same units).
3What does iodine stain blue-black?
4What should you use to show dense areas in a scientific drawing instead of shading?
5How should you carry a microscope?
With two hands: one on the arm, one under the base.
More practice: on your own
1A cell drawn 60 mm long is really 0.20 mm long. What is the drawing magnification?
2A drawing has a magnification of 250×. How long should a scale bar for 100 µm be?
100 µm × 250 = 25 000 µm = 25 mm.
3The FOV at 100× is 1.6 mm. A student sees 8 cells across at 400×. Estimate the cell length.
FOV at 400× = 1.6 × (100 ÷ 400) = 0.40 mm. Cell ≈ 0.40 ÷ 8 = 0.050 mm = 50 µm.
4A student shaded the xylem dark grey in her drawing to show it stained red. How should she fix it?
Remove the shading; outline the xylem cells with continuous lines and use stippling if needed, and add a label (e.g. "xylem, stained red") instead of colour or shading.
5Why are plant cross-sections often drawn as a sector (wedge) in a plan diagram?
A round cross-section repeats the same pattern all the way around, so drawing one wedge shows every tissue clearly and saves time, while allowing a larger, more detailed drawing.
Challenge
1A student estimates a cell is 150 µm using a field of view of 0.45 mm and a count of 3 cells. Her partner counts 3.5 cells. Calculate the partner's estimate and the percent difference between the two, relative to the first estimate. What does this tell you?
Partner: 0.45 mm ÷ 3.5 ≈ 0.129 mm ≈ 130 µm (2 significant figures). Difference: 150 − 129 = 21 µm; 21 ÷ 150 × 100% ≈ 14%. Counting cells across a field is a rough estimate: small differences in counting (especially part-cells) change the result a lot, so you should count several fields, average, and report the size to 2 significant figures at most.
2A photograph of a guard cell pair has a 20 µm scale bar that is 16 mm long on the page. The guard cell pair is 28 mm long on the page. How long is it really?
Magnification = 16 mm ÷ 20 µm = 16 000 µm ÷ 20 µm = 800×. Real length = 28 mm ÷ 800 = 0.035 mm = 35 µm.
3You want to compare the thickness of the palisade layer in sun leaves and shade leaves from the same maple tree. Describe how you would collect fair data with a microscope.
Use leaves from the same tree, collected on the same day, from the sunny (outer, south side) and shaded (inner) crown. Section several leaves of each type the same way, at the same spot (e.g. midway between midrib and edge). At the same magnification, measure palisade thickness with a calibrated scale (or count cells across a known FOV). Measure several leaves and several fields per leaf, calculate means, and compare. Keep everything else (stain, magnification, measurer) the same.
Quiz
1. A 10× eyepiece and a 4× objective give a total magnification of:
2. If the field of view is 2.0 mm at 100×, at 400× it is:
3. Which is a correct rule for scientific drawings?
5. A cell is 0.10 mm long and drawn 50 mm long. The drawing magnification is:
6. Which slide would best show stomata and guard cells?
Big idea: F2.3 asks students to identify and draw specialized plant tissues using a microscope and models. This lesson teaches microscope use and safety (A1.2, A1.4), measurement with the field of view and significant figures (A1.13), and scientific drawing conventions (A1.12).
How to help: A microscope is ideal but not required. Some public libraries lend them, and inexpensive student microscopes work well for onion skin and Elodea (pet stores sell Elodea for aquariums). Otherwise, use the home version: a grown-up cuts a thin celery slice, and a phone camera on maximum zoom does surprisingly well. Check drawings against the five rules; the most common slips are shading and crossed label lines.
Common difficulties:
- Unit mix-ups between mm and µm (multiply mm by 1000 to get µm).
- Dividing instead of multiplying when finding the field of view at higher power. Higher magnification always means a smaller field.
- Calculating drawing magnification with different units on top and bottom.