Unit 5 · Cells & Living Systems · Week 1
What makes something alive — and what is everything made of?
A seed and a pebble both sit in a cup of water on the sunny windowsill. Days later, the seed sprouts into a plant. What makes the seed alive when the pebble is not, and what is everything — seeds, pebbles, plants — made of?
Start here
How we work this lesson (our expectations)
- Wonder out loud — questions are the work
- Use evidence, not guesses
- Reasoning > being first or fastest
- Supports are for everyone — open any you want
30-second check-in self-management
Before we start, notice your focus right now. On a scale of 1 (foggy) to 5 (sharp), where are you? Take one slow breath. If you're at a 1 or 2, that's okay — the steps below are small on purpose, and you can listen to any part with the Listen button.
Do-Now Quick recall
Pull from what you already know — no looking back. Retrieval makes ideas stick.
- Unit 1 spiral: All matter is made of tiny particles too small to see. Name one example of solid matter, one of liquid matter, and one of gas matter that you can find in the room right now.
- Unit 3 spiral: Water moves through Earth's systems in a cycle. Name one place where liquid water changes into water vapor.
- Pre-assessment: If you had to explain to a younger student what makes something "alive," what would you say? (Best guess — we are building this idea today.)
The phenomenon
The seed and the pebble started the week in identical conditions — the same plastic cup, the same tap water, the same patch of sunlight. By Friday, the pebble looks exactly as it did on Monday. The seed has cracked open and a pale green shoot is curling upward. Something inside the seed — something the pebble definitely does not have — has been taking in water, rearranging matter, and using stored energy to grow. Whatever that something is, it is what we mean by "alive." Our question today: what exactly is happening inside the seed that makes it count as a living thing?
A pebble and a seed sat in the same cup of water by the window all week. The pebble did nothing. The seed cracked open and grew a green shoot. Something inside the seed — something the pebble does not have — used water and stored energy to grow. What is that something, and what makes the seed alive?
Notice & Wonder. Write one thing you notice and one thing you wonder. Keep your wonder — we are answering it today.
Build it Three big ideas, one small step at a time
We will build the answer in steps. After each step there is a quick check before we move on.
Step 1 — Same atoms, different organization
All matter — the seed, the pebble, your hand, the air — is made of the same kinds of tiny particles: atoms of carbon, hydrogen, oxygen, nitrogen, and a few others. Living things do not have special atoms that rocks lack. The difference between something alive and something not alive is not what atoms it contains, but how those atoms are organized. In Unit 1 we said matter is made of particles too small to see. Every living cell — and every rock — is built from those same particles. The seed and pebble share many of the same atomic ingredients. What the seed has that the pebble does not is a highly organized system of structures that use those atoms to carry out life processes.
The seed and the pebble are both made of tiny particles — atoms. The same kinds of atoms are in living things and in rocks. The difference is how the atoms are organized. A seed has organized structures inside it that use atoms to do life's work. A pebble does not. Same atoms — completely different organization.
Step 2 — The cell: the smallest unit that is alive
Scientists define the cell as the basic unit of life — the smallest unit that carries out all life processes on its own. Every living thing is made of one or more cells. A bacterium is a single cell. A tree is made of trillions of cells. You are made of roughly 37 trillion cells. The seed contains living cells; the pebble contains no cells at all. This is the fundamental difference. No cells = not alive, no matter what atoms are present.
The cell is the smallest unit that is alive. Every living thing — a bacterium, a tree, you — is made of cells. A seed has living cells inside it. A pebble has no cells. That is the key difference. Cells are what make something alive.
Step 3 — Seven characteristics of life
Scientists use seven characteristics to define what counts as alive. If something meets all seven, it is considered a living thing (an organism). If it fails even one — if it has no cells, or if it cannot reproduce, or if it has no hereditary code — it is not considered alive. Here are the seven, with the seed and the pebble side by side:
Scientists use seven characteristics to define life. Something is alive if it meets all seven. Here they are, with the seed and the pebble compared:
Worked example — seed vs. pebble across all 7 characteristics of life
1. Made of cells — Seed: yes (filled with living cells). Pebble: no (mineral crystals, no cells).
2. Uses energy — Seed: yes (uses stored energy in the seed to power growth). Pebble: no (energy passes through it as heat, but it does not use energy for internal processes).
3. Grows and develops — Seed: yes (crack open, shoot emerges, roots grow down). Pebble: no (may erode, but that is a physical change from outside, not internal development).
4. Responds to the environment — Seed: yes (the shoot bends toward light; roots grow toward water). Pebble: no (it sits there regardless of light or water).
5. Reproduces — Seed: yes (it will eventually produce flowers and new seeds). Pebble: no (it cannot make copies of itself).
6. Maintains homeostasis — Seed: yes (cells regulate their internal water balance). Pebble: no (its internal state depends entirely on external conditions).
7. Has a hereditary code (DNA) — Seed: yes (every cell contains DNA that carries the instructions for building a plant). Pebble: no (no DNA; no instructions; no code).
Important note on dormancy: When a seed is dry and sitting on a shelf, it looks exactly like the pebble — nothing seems to be happening. But the seed is still alive. Its cells are in a low-activity state called dormancy, waiting for the right conditions (water, warmth) to activate. Dormancy is not death. The seed still has cells, still has DNA, and still maintains its internal organization. When conditions are right, it resumes all seven life processes. The pebble has never had any of the seven — not even while doing nothing.
1. Made of cells — Seed: yes. Pebble: no.
2. Uses energy — Seed: yes. Pebble: no.
3. Grows and develops — Seed: yes. Pebble: no.
4. Responds to the environment — Seed: yes (grows toward light). Pebble: no.
5. Reproduces — Seed: yes. Pebble: no.
6. Maintains homeostasis — Seed: yes. Pebble: no.
7. Has DNA — Seed: yes. Pebble: no.
Dormancy note: A dry seed sitting on a shelf looks like it's not alive — but it is. Its cells are resting, waiting for water and warmth. When conditions are right, it wakes up. The pebble has never had any of the seven — ever.
Show me the 7 characteristics as a table I can fill in Tier 2 · visual organizer
Copy this table into your notebook and fill in the Seed and Pebble columns:
Characteristic | Seed (yes/no + why) | Pebble (yes/no + why)
1. Made of cells | ___ | ___
2. Uses energy | ___ | ___
3. Grows and develops | ___ | ___
4. Responds to environment | ___ | ___
5. Reproduces | ___ | ___
6. Maintains homeostasis | ___ | ___
7. Has DNA | ___ | ___
After filling in the table: count how many "yes" answers the seed has. Count how many "yes" answers the pebble has. The difference tells you what it means to be alive.
Your turn Explain what makes the seed alive
Use a Claim–Evidence–Reasoning model to answer our question. Choose how you respond — all are equally valid.
The task: Why is the sprouting seed alive and the pebble is not? Make a claim, give evidence from what we built (use at least 3 of the 7 characteristics), and explain your reasoning using the words "cells," "energy," and "matter."
I want sentence starters and a word bank Tier 2 · frames
Claim: The seed is alive and the pebble is not because ________.
Evidence: I know this because the seed ________ while the pebble ________.
Reasoning: This matters because living things must ________ and ________, which the seed does but the pebble does not.
Word bank: cells · energy · matter · grow · reproduce · respond · homeostasis · DNA · particles · organized
Let's make it concrete first Tier 3 · re-teach
Analogy — a city vs. a rock: A city is made of the same materials as the surrounding rock — concrete, metal, sand — but a city is organized completely differently. It has workers, energy flowing through it, systems to take in food and remove waste, and plans passed down to new generations. A cell is to a rock as a city is to a pile of rubble — same atoms, completely different organization. The seed is a city. The pebble is a pile of rubble.
Fill in: The seed is alive because it is organized into ________ that use ________ and ________ to carry out life processes. The pebble has none of these structures.
Say your answer out loud before you write it. One sentence is enough to start.
Push my thinking Extension
Look up the "cell theory" — who developed it, when, and how the microscope made it possible. Connect this to our phenomenon: the seed's cells were invisible to people for thousands of years before the microscope was invented. Write a paragraph explaining how the microscope changed what "alive" means scientifically — and what humans must have thought made seeds alive before cells were discovered.
Check yourself Did it click?
- explain that all matter (living and non-living) is made of the same kinds of atoms — the difference is organization;
- name the cell as the basic unit of life and explain why having cells defines something as alive;
- use at least three of the seven characteristics of life to explain why the seed is alive and the pebble is not.
Which of the following BEST explains why the sprouting seed is alive and the pebble is not?
Re-teach: why movement and growth alone don't define life Tier 3
Two common misconceptions:
Misconception 1 — "Movement = life." A fire moves and spreads. Wind moves. Clouds move. None of these are alive. A dormant seed doesn't visibly move at all — but it is alive. Movement can be a sign of life, but it is not the definition.
Misconception 2 — "Growth = life." A crystal grows in a supersaturated solution. A stalactite grows in a cave. A fire grows when it finds more fuel. None of these are alive. Growth can be a sign of life, but it is not the definition either.
What actually defines life: Go back to the 7 characteristics — and especially the cell criterion. The most important test is: does it have cells? Only living things have cells. A cell is the smallest unit that carries out all life processes — taking in energy, responding to the environment, maintaining homeostasis, carrying DNA. A fire has none of these. A dormant seed has all of them, even when it looks completely still.
Re-read option B. It names cells and life processes. That is the correct definition. Try saying it in your own words before moving on.
Reflect, then show what you know
Reflection metacognition + SEL
Which support did you use today (if any), and did it help? There's no wrong answer — noticing what helps you learn is a skill scientists use too.
Exit ticket — answer on paper or in your notebook.
- New Name three characteristics of life and explain how the sprouting seed shows each one.
- New The cell is called the "basic unit of life." In your own words, what does "basic unit" mean, and why is a cell considered the smallest living thing?
- Spiral — Unit 1 A cell contains water, proteins, and gases. All of these are matter. What does that tell you about the relationship between living things and the particles we studied in Unit 1?
- Spiral — Unit 1 In Unit 1 we said energy is never created or destroyed — it moves from place to place. How does the sprouting seed connect to that idea? Where did the energy come from to push that shoot upward?
- Transfer → Week 2 The seed needs water, sunlight, and air to grow. Predict: what do you think the seed's cells are doing with those three things? We'll find out next week.
Educator panel — facilitation, accommodations, answer key
At a glance
Standard: NGSS 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. 3D: SEP Developing & Using Models · DCI LS1.A Structure & Function (the cell as the basic unit of life) · CCC Energy & Matter (living things take in matter and energy). Throughline: Launches the unit's driving question — what does it mean to be alive, and how do living systems use matter and energy? — and connects directly to Unit 1's particle model of matter.
Materials (optional, fully digital-capable): A real seed and pebble in a cup of water (optional, powerful visual anchor); student notebook. No lab required. If seeds are available, start the germination cup on Monday for a Friday reveal.
Facilitation arc (Rosenshine)
- Launch phenomenon before any vocabulary — let the contrast be theirs (3 min).
- Do-Now retrieval while you take attendance (3 min).
- Build Steps 1–3 with the worked example; stop and check after each step (12 min).
- Differentiated CER practice — circulate; note which tier supports students reach for (15 min).
- Self-check + re-teach branch for any A or C responders (5 min).
- Brain break (2 min).
- Reflection + exit ticket (10 min).
IEP / 504 accommodation cards
Common accommodations mapped to this lesson
| Accommodation | How it's already built in / what to do |
|---|---|
| Text read aloud | Every passage has a Listen button (TTS via Web Speech API); the simplified toggle shortens all passages. |
| Reduced reading load | "Reading: Simplified" swaps in plain-language text throughout, including the worked example. |
| Chunking / extended time | Lesson is in three clearly labeled steps with checks; progress saves automatically — students can stop and resume. |
| Sentence frames / word bank | Tier-2 support panel provides frames for Claim, Evidence, and Reasoning, plus a 10-word word bank. |
| Concrete analogy / reduced load | Tier-3 "city vs. rock" analogy provides a cloze frame; connects to prior knowledge without requiring new vocabulary. |
| Alternative response mode | Students may draw a model, speak/record, or write the CER — all three are explicitly accepted as equally valid. |
| Behavior / focus (504, ADHD) | Named expectations (PBIS), 30-sec check-in, and a built-in brain break with purposeful movement. |
| Multilingual / EL | Simplified text toggle, SVG visual anchor showing seed vs. pebble, word bank in Tier-2, home-language reflection is allowed. |
Exit ticket answer key
- Any three from the seven: e.g., "Made of cells — the seed contains living cells; uses energy — it uses stored energy to push the shoot up; responds to environment — the shoot bends toward the light." Full credit for any three with a brief "how" for each.
- "Basic unit" means the smallest piece that is still alive and can do everything a living thing does. A cell is the smallest unit because if you break it into smaller pieces (molecules, atoms) those pieces are not alive — they cannot carry out life processes on their own.
- Living things are made of the same kinds of particles (atoms, molecules) that everything else is made of — the same Unit 1 particles. Life is not made of special atoms; it is made of ordinary atoms organized in an extraordinary way.
- The energy came from somewhere else — specifically, from the chemical energy stored in the seed's food reserves (sugars and fats) during the time the parent plant was making the seed. Energy was not created; it was transferred from stored chemical energy into the mechanical energy of growing cells. (Preview: next week students will learn that the plant uses sunlight to make that stored energy via photosynthesis.)
- Accept any reasonable prediction: "The cells use sunlight for energy," "the cells use water to make food," "the air gives the plant carbon to build its body," etc. The key is the prediction — no wrong answers here; this is the setup for Week 2.
Why it's designed this way
Phenomenon-first (NRC, 2012): the seed-vs.-pebble contrast is everyday, free to set up, and genuinely three-dimensional — it cannot be resolved without integrating cells (DCI), a model (SEP), and the matter-and-energy framework (CCC). The Do-Now deliberately reaches back to Unit 1's particle model so students arrive at "same atoms, different organization" rather than being told it. The dormancy note directly addresses the most common misconception (seeds are "not alive" because they don't move), which appears in the self-check. The worked example uses a side-by-side format to prevent cognitive overload while still covering all seven characteristics. The city-vs.-rock analogy in Tier-3 gives concrete-operational thinkers a spatial anchor before abstract cell theory. The exit ticket item 5 is a transfer-forward item that seeds the Week 2 phenomenon without giving away the answer, maintaining the unit's storyline.