Start low
Click the scanning (4×) objective into place. Raise the condenser and open the iris diaphragm; turn on the light.Lab 2 gives you the tool you will use for the rest of the semester, the compound light microscope, and then points it at cells. You will name microscope parts and their jobs, calculate magnification, focus a slide the right way, identify cell structures on a model, and pick out each stage of mitosis on onion root tip and whitefish blastula slides.
Your lab manual wins. Lab sections vary in which models, slides, and terms they use. If anything here differs from your lab handout or what your instructor emphasized, go with your lab material and tell your tutor so this review can be updated.
Concept Review · The Microscope
| Part | What it does | How to spot it |
|---|---|---|
| Ocular lens (eyepiece) | The lens you look through; usually magnifies 10× | Top of the scope, angled toward you |
| Head / body tube | Holds the ocular and keeps the lenses aligned | Connects the eyepiece to the nosepiece |
| Revolving nosepiece (turret) | Rotates to click a different objective into place | Rotating disc the objectives hang from |
| Objective lenses | Primary magnifying lenses: scanning 4×, low 10×, high 40×, oil immersion 100× | Longer barrel = higher power; color bands often red, yellow, blue, white |
| Stage | Flat platform that holds the slide; has a hole for light to pass | Below the objectives |
| Stage clips / mechanical stage | Hold the slide; mechanical stage knobs move it left-right and forward-back | Spring clip on the stage; knobs hanging under the stage |
| Coarse adjustment knob | Moves the stage (or tube) a lot for rough focus; scanning and low power only | Larger knob on the arm |
| Fine adjustment knob | Small movements for sharp focus; the only focus knob used at high power and oil | Smaller knob, often on the same axle as the coarse knob |
| Condenser | Lens under the stage that focuses light onto the specimen | Short cylinder directly under the stage opening |
| Iris diaphragm (lever) | Opens or closes to control how much light reaches the specimen (and contrast) | Lever sticking out of the condenser |
| Light source (illuminator) | Lamp that sends light up through the specimen | In the base under the condenser |
| Arm and base | Structural support; carry it by the arm with a hand under the base | Curved back piece; heavy bottom |
Naming varies: some manuals say eyepiece for ocular, turret for nosepiece, substage light or lamp for the illuminator, and simply diaphragm for the iris diaphragm. Older scopes have separate coarse and fine knobs; many newer ones put them on one axle. Your practical accepts the common alternatives.
Label It · Microscope
Side view of a compound microscope. Click a pin, choose the part, then press Check answers.
Concept Review · Using the Microscope
| Objective | Ocular | Total magnification | Focus with |
|---|---|---|---|
| Scanning 4× | 10× | 40× | Coarse, then fine |
| Low power 10× | 10× | 100× | Coarse (carefully), then fine |
| High power 40× | 10× | 400× | Fine only |
| Oil immersion 100× | 10× | 1000× | Fine only, with immersion oil |
Total magnification = ocular power × objective power. If your ocular is 15× instead of 10×, the 40× objective gives 600×.
| As magnification goes up… | What happens |
|---|---|
| Field of view (diameter of the circle you see) | Decreases: you see a smaller area, larger |
| Brightness | Decreases: open the iris diaphragm |
| Depth of field (thickness in focus at once) | Decreases: focus up and down with the fine knob to see layers |
| Working distance (lens to slide) | Decreases: why the coarse knob is dangerous at high power |
| Movement | Image moves opposite to the way you push the slide |
Field-of-view math: diameter shrinks in proportion to magnification. If the field is 4.5 mm at 40×, at 400× it is 4.5 ÷ 10 = 0.45 mm (450 µm).
Concept Review · The Cell
| Structure | Function | What it looks like on a model |
|---|---|---|
| Plasma membrane | Phospholipid bilayer with proteins; selectively permeable boundary | Outer edge of the cell |
| Cytoplasm | Everything between the membrane and nucleus: cytosol (fluid) plus organelles | The “background” filling the cell |
| Nucleus | Holds DNA (chromatin); control center | Largest round organelle |
| Nuclear envelope | Double membrane with pores around the nucleus | Border of the nucleus, with gaps (pores) |
| Nucleolus | Makes ribosomal subunits (rRNA) | Dark dot inside the nucleus |
| Ribosomes | Build proteins | Tiny dots, free in cytoplasm or on rough ER |
| Rough ER | Makes and folds proteins for export or membranes | Stacked, folded membranes studded with dots, next to the nucleus |
| Smooth ER | Makes lipids and steroids; detoxifies; stores Ca2+ | Tubular network without dots |
| Golgi apparatus | Modifies, sorts, and packages proteins into vesicles | Stack of curved flattened sacs with vesicles budding off |
| Mitochondrion | Makes most of the cell’s ATP (cellular respiration) | Oval with folded inner membrane (cristae) |
| Lysosome | Digestive enzymes break down debris and worn organelles | Small round sac, often darker |
| Centrioles | Pair of cylinders in the centrosome; organize the mitotic spindle | Two small barrels at right angles near the nucleus |
Rough vs. smooth ER is the classic model mix-up. Rough = dots (ribosomes) and flattened sheets right next to the nucleus. Smooth = no dots, tubes, farther out. The Golgi looks similar to rough ER but has no dots, is curved like a stack of pancakes, and sits farther from the nucleus with vesicles at its edges.
Label It · Cell
Generalized animal cell. Click a pin, choose the structure, then press Check answers.
Concept Review · Osmosis
Osmosis is the passive movement of water across a selectively permeable membrane toward the side with more solute (less water). Tonicity compares the solute concentration of a solution to the inside of the cell.
| Solution | Compared to the cell | Water moves | Red blood cell result | Example |
|---|---|---|---|---|
| Hypotonic | Fewer solutes outside | Into the cell | Swells; may burst (hemolysis) | Distilled water |
| Isotonic | Same solute concentration | No net movement | Normal biconcave disc | 0.9% NaCl (normal saline) |
| Hypertonic | More solutes outside | Out of the cell | Shrinks and wrinkles (crenation) | Strong salt solution (e.g., 5% NaCl) |
Hook: hypo sounds like “hippo”: the cell gets big. Water always chases solute.
Concept Review · Cell Cycle
The cell cycle is interphase (G1 growth, S DNA copying, G2 preparation) followed by the mitotic phase: mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm). Most cells on any slide are in interphase because it is by far the longest stage.
| Stage | What is happening | What you see on the slide |
|---|---|---|
| Interphase | Cell grows; DNA replicates; not dividing | Intact round nucleus, grainy chromatin, one or more dark nucleoli; no visible chromosomes |
| Prophase | Chromatin condenses into chromosomes (sister chromatids); nucleolus and nuclear envelope break down; spindle forms | Thick, dark, tangled threads where the nucleus was; nucleus outline fading |
| Metaphase | Chromosomes line up on the metaphase plate (equator), attached to spindle fibers | A dark band of chromosomes across the middle of the cell |
| Anaphase | Sister chromatids separate and move to opposite poles | Two V-shaped groups pulling apart, arms trailing toward the center |
| Telophase | Chromosomes uncoil; new nuclear envelopes and nucleoli form at each pole | Two dark masses at opposite ends of one cell |
| Cytokinesis | Cytoplasm divides (usually begins in late anaphase or telophase) | Animal: cleavage furrow pinching in. Plant: cell plate forming across the middle |
Prometaphase: some courses add a stage between prophase and metaphase when the nuclear envelope is gone and chromosomes attach to spindle fibers. If your lab does not list it, a cell like this is called late prophase. Mnemonic for order: I Picked My Apples Today (Interphase, Prophase, Metaphase, Anaphase, Telophase).
Concept Review · The Two Classic Slides
| Feature | Onion (Allium) root tip | Whitefish blastula |
|---|---|---|
| Why this tissue? | The root tip meristem divides constantly to grow the root | The early embryo (blastula) divides rapidly |
| Cell type | Plant cell | Animal cell |
| Cell shape | Brick-like rectangles in neat rows (files), with a cell wall | Rounded cells, no cell wall |
| Centrioles and asters | None (spindle still forms) | Asters (starburst rays around the centrosomes) are easy to see |
| Spindle fibers | Faint | Clearly visible lines from pole to chromosomes |
| Cytokinesis | Cell plate forms in the middle and becomes a new wall | Cleavage furrow pinches the cell in two |
| Best power | Scan to find the zone just behind the root cap, then 40× | Find the round section on scanning, then 40× |
Practical strategy: ignore the color first and look at the chromosomes. No chromosomes and an intact nucleus = interphase. Tangled = prophase. A line = metaphase. Two groups moving apart in one cell = anaphase. Two groups far apart with new nuclei, plus a plate or furrow = telophase.
Watch for this trick: two small cells side by side, each with an interphase nucleus, are two daughter cells after cytokinesis, not one cell in telophase. Look for a shared cell outline.
Label It · Onion Root Tip
Field of view at 400×. Each pin points to one cell, or to a structure within a cell. Name the stage or structure.
Label It · Whitefish Blastula
Field of view at 400×. Notice that the dividing cells point in different directions, just as on a real slide.
Check Yourself
Two tries per question. Read the explanation each time.
Rapid Recall
Say the answer out loud, then tap the card to check. Shuffle and go again until every card is automatic.
Practical Simulation
This runs like a real lab practical: one structure or question per station, a timer, and you type the answer — no word bank. Spelling counts on most practicals, so spell it fully. Your score and every correct answer appear at the end.
20 stations · 50 seconds each · stations come in random order every attempt.
| # | Station | Your answer | Correct |
|---|
Watch Out
| The mistake | The fix |
|---|---|
| Using the coarse knob at 40× or 100×. | Coarse only on scanning and low power. At high power, fine knob only, or you can crack the slide and scratch the lens. |
| Forgetting to multiply by the ocular. | Total magnification = ocular × objective. The objective number alone is not the answer. |
| Mixing up the condenser and the iris diaphragm. | Condenser = lens that focuses light. Iris diaphragm = the adjustable opening (lever) that controls how much light. |
| Not centering before switching to higher power. | The field shrinks as power increases; center the target first or it disappears. |
| Calling the Golgi “rough ER” on a model. | Rough ER has ribosome dots and hugs the nucleus. Golgi is a curved stack with vesicles and no dots. |
| Calling a prophase cell “interphase.” | Interphase has a smooth, intact nucleus with a nucleolus. Visible thread-like chromosomes = prophase. |
| Confusing late anaphase with telophase. | Anaphase: groups still moving, V shapes. Telophase: groups at the poles, clumping into new nuclei, plate or furrow visible. |
| Writing “cleavage furrow” for the onion. | Plants form a cell plate. Cleavage furrow is for animal cells such as the whitefish blastula. |
| Swapping hypotonic and hypertonic. | Water chases solute. Hypotonic outside = water rushes in = swelling and hemolysis. Hypertonic = crenation. |
Cheat Sheet
Print it or screenshot it for a last look before the lab.
| Topic | Know this |
|---|---|
| Light path | Light source → iris diaphragm/condenser → stage opening → slide → objective → body tube → ocular |
| Objectives | Scanning 4× (40× total), low 10× (100×), high 40× (400×), oil 100× (1000×) |
| Focus knobs | Coarse = scanning/low only. Fine = all powers; only knob at high and oil |
| Light control | Iris diaphragm (amount of light); condenser (focuses light) |
| More magnification | Smaller field of view, dimmer, shallower depth of field, shorter working distance |
| Image | Inverted and reversed; moves opposite to the slide |
| Focusing steps | Scanning objective → slide on stage → coarse then fine → center → switch up (parfocal) → fine only → more light |
| Organelles | Nucleus (DNA), nucleolus (ribosome subunits), ribosomes (protein), rough ER (protein), smooth ER (lipids, detox), Golgi (package), mitochondria (ATP), lysosome (digest), centrioles (spindle) |
| Tonicity | Hypotonic: swells, hemolysis. Isotonic: no change (0.9% NaCl). Hypertonic: crenation |
| Cell cycle | Interphase (G1, S, G2) → prophase → metaphase → anaphase → telophase → cytokinesis |
| Stage clues | Intact nucleus = interphase; tangled = pro; line = meta; V groups apart = ana; two new nuclei + plate/furrow = telo |
| Onion root tip | Plant: brick-shaped cells, cell wall, no asters, cell plate |
| Whitefish blastula | Animal: round cells, asters and spindle visible, cleavage furrow |
Debrief
You can now run the microscope, name what you see in a cell, and stage a dividing cell on sight. Next is Lab 3, histology, where you use the same microscope skills to identify the four tissue types.
💭 Before the real thing: run the practical simulation until you score 90% or better twice in a row. Then do it once with the timer on.