Lesson Q3 L1 – Living Things Are Made of Cells
Lesson Overview
Quarter 3 · Unit 3A: Cells and Plant Structures · Week 19 · Grades 6–8 · Lesson length: 50 minutes
Essential Question: What evidence shows that the plants in our garden, and all living things, are made of cells?
Lesson Focus: Students learn to use a compound microscope, prepare wet mounts of onion skin and a garden leaf (or Elodea), sketch cells at two magnifications, and connect observations to cell theory.
Why It Matters: Cell theory is the foundation of biology. Seeing cells in plants students grew makes the abstract idea concrete and starts the zoom from whole plant to cell that frames Quarter 3.
Source: New lesson written for this series (2026).
Standards & Learning Targets
Standards Alignment
NGSS Middle School Performance Expectations: MS-LS1-1 — Conduct an investigation to provide evidence that living things are made of cells; either one cell or many different numbers and types of cells
Science & Engineering Practices / Crosscutting Concepts: Planning and Carrying Out Investigations; Obtaining, Evaluating, and Communicating Information; Scale, Proportion, and Quantity (CCC); Structure and Function (CCC)
Student Learning Targets
Learning Targets — students will be able to
Use a compound microscope safely to focus on a specimen at low and medium power
Prepare a wet mount and draw cells with labels and magnification
Use observations to support the three parts of cell theory
Key Vocabulary
cell · cell theory · microscope · magnification · wet mount · specimen · unicellular · multicellular
Materials & Teacher Prep
| Materials Needed | Teacher Prep Checklist |
|---|---|
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Low-Cost Option: Not enough microscopes? Run a station rotation or project one microscope through a phone camera held to the eyepiece. A clip-on phone macro lens shows larger cells such as onion skin.
Safety: Goggles and gloves for iodine, which stains skin and clothing and irritates eyes; the teacher dilutes and dispenses it in dropper bottles. Report broken slides or cover slips; the teacher cleans glass with a brush and dustpan. Carry microscopes with two hands, and never aim a microscope mirror at direct sunlight. See Appendix I.
Equipment Procedure — Compound microscope and wet mount
- Carry the microscope with two hands, one on the arm and one under the base.
- Place a thin onion layer on the slide, add one drop of iodine, and lower a cover slip at an angle to avoid bubbles.
- Start on the lowest-power objective, center the specimen, and focus with the coarse knob while watching from the side so the lens does not hit the slide.
- Look through the eyepiece and focus with the fine knob only; switch to medium power and refocus with the fine knob.
- Total magnification = eyepiece × objective; record it on your sketch; clean slides and return the microscope on low power.
Lesson Flow & Timing
| Engage · 5 min | Explore · 20 min | Explain · 10 min | Elaborate · 10 min | Evaluate · 5 min |
|---|---|---|---|---|
| Hidden building blocks | Microscope lab (RallyCoach) | Cell theory | Labeled sketches | Exit ticket |
Phase 1 · Engage — The Hook
Teacher Talk
PCM: Curiosity. Hold up a radish. “This radish is made of millions of tiny rooms. Nobody saw them until about 360 years ago, when Robert Hooke looked at cork through a microscope and called them ‘cells.’ Today we see them ourselves.” Name cell, cell theory, microscope, and magnification before the work starts, then return to them in Explain.
Ask Students
“What do you think a plant cell looks like?” “Are all living things made of the same building blocks?” “What would count as evidence?”
PCM Differentiation
Thinker Students: If the eyepiece is 10× and the objective is 40×, what is the total magnification? An onion cell looks 12 mm long at that magnification; how long is it actually? (Illustrative data.)
Harmonizer Students: Scientists across centuries built cell theory together, each adding evidence. How does scientific knowledge depend on people sharing work?
Phase 2 · Explore — Kagan Cooperative Activity
Cooperative Structure
Kagan structure: RallyCoach. Partners alternate preparing, focusing, and coaching at the microscope, switching roles for each specimen so both master the procedure (See the Teaching Reference for the structure’s steps.) Have students jot wet mount and specimen at the top of their notes; Explain will define them precisely.
Step-by-Step
- Step 1 — Practice (5 min): Partner A focuses the demonstration slide on low power while B coaches using the equipment procedure; switch.
- Step 2 — Onion mount (7 min): Partner B prepares an onion wet mount while A coaches; both sketch cells at low and medium power.
- Step 3 — Leaf mount (6 min): Partner A prepares a thin leaf peel or Elodea mount while B coaches; both sketch and look for green chloroplasts.
- Step 4 — Compare (2 min): Partners list similarities between the two specimens.
Teacher Moves During Explore
Check that students start on low power and focus with the coarse knob only at low power
Ask, “What shape are the cells? How are they arranged?”
Ask, “What is the green inside the leaf cells?”
Phase 3 · Explain — Direct Instruction
Mini-lesson — Cell theory. Teacher move: Present the three statements with the scientists who contributed (Hooke, van Leeuwenhoek, Schleiden, Schwann, Virchow) and connect each to today’s observations.
Cell: the smallest unit that can carry out all the processes of life
Cell theory: (1) all living things are made of one or more cells; (2) the cell is the basic unit of structure and function; (3) all cells come from existing cells
Unicellular and multicellular: bacteria and many protists are one cell; plants and animals are made of many different types of cells
Microscopes: magnification makes small objects appear larger; resolution lets us see detail
Evidence: onion and leaf cells have boundaries, a nucleus (seen with stain), and repeated structure, supporting cell theory
Key Message: All living things are made of cells, cells are the basic units of life, and new cells come from existing cells. Microscopes let us collect the evidence ourselves.
Check for Understanding — Ask Students
“What are the three parts of cell theory?” “Calculate total magnification for a 10× eyepiece and 10× objective.” “What is the difference between unicellular and multicellular organisms?”
Phase 4 · Elaborate — Student Product & Differentiation
Student Product
Each student produces two labeled cell sketches with magnification and writes how the observations support cell theory.
Differentiation
| Grade 6 focus | Grade 7 focus | Grade 8 focus |
|---|---|---|
| Use the microscope and sketch cells with labels and magnification. | Explain how observations support each part of cell theory. | Calculate actual cell size from magnified size and evaluate the limits of a light microscope. |
Support (scaffolded entry): Provide a microscope diagram and a sketch template with circles and label lines.
Challenge Extension: Research how electron microscopes changed what we know about cells and compare their magnification with ours.
Multilingual Learners: Labeled microscope diagram; cognates célula, microscopio, magnificación, teoría.
Phase 5 · Evaluate — Closure, Exit Ticket & Assessment
Exit Ticket
- State the three parts of cell theory.
- What total magnification did you use for your best sketch?
- Name one observation that shows the leaf is made of cells.
Answer Key / Look-Fors: (1) All living things are made of cells; cells are the basic unit; cells come from cells. (2) For example, 100× or 400×. (3) Repeated box-like units with walls, nuclei, chloroplasts.
Grade-Level Practice Items
Grade 6. Which statement is part of cell theory?
A) Only animals are made of cells. B) All cells come from existing cells. C) Cells are made of organs. D) Cells form from nonliving matter.
Answer: B — Cells arise from existing cells.
Grade 7. A microscope has a 10× eyepiece and a 40× objective. What is the total magnification?
A) 50× B) 140× C) 400× D) 4,000×
Answer: C — 10 × 40 = 400×.
Grade 8. An onion cell appears 20 mm long at 100× magnification. What is its actual length? (Illustrative data.)
A) 0.02 mm B) 0.2 mm C) 2 mm D) 2,000 mm
Answer: B — 20 mm ÷ 100 = 0.2 mm.
Grade-Level Short Response (for quizzes and tests)
Grade 6. Describe two observations from today’s lab that show plants are made of cells.
Look-for: Box-shaped units with walls, nuclei, repeated pattern, chloroplasts in leaf cells.
Grade 7. Explain how observations of onion and leaf cells provide evidence for cell theory.
Look-for: Both made of cells; cells show structure and function; cells look alike and form tissues.
Grade 8. Explain why scientists use the actual size of a cell rather than its magnified size, and calculate an example.
Look-for: Magnified size depends on lens; actual = image size ÷ magnification; example correct.
Expanding Circles
How does this connect to… Self — What part of your body would you like to see under a microscope? • Classroom — How will cells explain our radish growth? • School — Who uses microscopes in our community (doctors, labs)? • Community — How do Arizona labs use microscopes for agriculture? • World — How did cell theory change medicine worldwide?
Formative Assessment
Formative Assessment (evidence for sorting students: the two labeled cell sketches with magnification, the exit-ticket cell theory, and the grade-level practice items)
Meets (3): Two labeled sketches with correct magnification and an explanation tied to all three parts of cell theory.
Approaching (2): Sketches present but labels or magnification missing.
Not Yet (1): Cannot focus; reteach the procedure one-on-one at low power.
Extend & Looking Ahead
To close, show your grade’s 1-minute recap video: Grade 6; Grade 7; Grade 8.
Extension: Observe pond water or compost tea for single-celled organisms.
Looking Ahead: In Lesson 3.2 we zoom in on the parts inside plant cells and what each one does.