Unit 5 · Cells & Living Systems · Week 4
How do trillions of cells work as one body?
Your body has roughly 37 trillion cells, and every single one needs a constant supply of oxygen and glucose. How does the body make sure every cell gets what it needs — and how does a cut heal when individual cells are damaged?
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 what you remember from last week. On a scale of 1 (completely blank) to 5 (I could teach it), where are you on cellular respiration? Take one breath — this lesson builds directly on that idea, and the supports are here if you need to reconnect. You are not starting from zero.
Do-Now Quick recall
Pull from what you already know — no looking back. Retrieval makes ideas stick.
- W3 spiral Write the word equation for cellular respiration. What two raw materials does every cell need to perform it?
- W2 spiral In photosynthesis, where does the carbon that becomes the plant's body come from? Name the specific molecule.
- W1 spiral The cell is the "basic unit of life." Name two organelles and their functions from last week.
The phenomenon
When you get a small cut, something remarkable happens in the next few days: the bleeding stops, the wound seals, new skin cells grow to fill the gap, and eventually the cut disappears entirely. Millions of cells — blood cells, immune cells, skin cells, muscle cells — each doing a different job, each communicating with neighboring cells, each needing its own supply of oxygen and glucose delivered by the circulatory system and its own waste taken away. No single cell can do all of this alone. Living things — from a tiny worm to a human — solve the problem of running trillions of cells as one body through levels of organization: cells → tissues → organs → organ systems → the organism.
A small cut heals in a few days. Millions of different cells — blood cells, skin cells, immune cells — each do their own job. But every one of those cells needs oxygen and glucose delivered to it, and every one needs its waste removed. No single cell can do all of this. Living things solve this with levels of organization: cells → tissues → organs → organ systems → organism. Each level does something the level below cannot do alone.
Notice & Wonder. Write one thing you notice and one thing you wonder. Keep your wonder — we are building toward it today.
Build it From single cells to a whole organism, one level at a time
We will build the answer in steps. After each step there is a quick check before we move on.
Step 1 — The five levels of organization
Living things are organized from the simplest to the most complex in five levels. A cell is the basic unit of life — the smallest thing that can carry out life processes (Week 1). A tissue is a group of similar cells all doing the same job; muscle tissue, nervous tissue, and epithelial tissue (skin) are examples. An organ is a structure made of two or more different types of tissue working together for a specific function — the heart is mostly cardiac muscle tissue; the skin is epithelial tissue over connective tissue; the lungs combine epithelial tissue, cartilage, and blood tissue. An organ system is a group of organs working together for a larger body function — the circulatory system (heart + blood vessels + blood) and the respiratory system (lungs + airways + diaphragm) are two examples. Finally, the organism is all systems working together as one living thing.
Five levels, smallest to largest: Cell — the basic unit of life. Tissue — similar cells doing the same job (e.g., muscle tissue). Organ — different tissues working together (e.g., the heart is muscle tissue + connective tissue). Organ system — organs working together (e.g., the circulatory system: heart + blood vessels + blood). Organism — all systems working together = you.
Step 2 — Structure and function at every level
A key idea from Week 3 (and from Week 1): structure determines function — and this principle works at every level of organization. A red blood cell is disc-shaped with a dimple (biconcave) to maximize surface area, allowing it to carry as much oxygen as possible. A neuron (nerve cell) is long and branching to transmit electrical signals across long distances. The lung's surface is covered with millions of tiny air sacs called alveoli to maximize the surface area available for gas exchange. At every level, the physical structure of a cell, tissue, or organ is precisely matched to the function it performs.
Structure matches function at every level. A red blood cell is disc-shaped to carry maximum oxygen. A neuron is long and branching to send signals far. The lungs have millions of tiny air sacs to maximize gas-exchange surface area. In each case, the shape of the structure enables its job.
Step 3 — The integrated delivery system for matter and energy
Every cell in the body does cellular respiration (Week 3). That means every cell needs two things delivered continuously: oxygen and glucose. It also needs its waste (CO₂, water) removed. No single system does all of this — three organ systems work together as an integrated delivery system. The respiratory system (lungs, airways, diaphragm) brings oxygen in from the air and removes CO₂. The digestive system (stomach, intestines) breaks food down and absorbs glucose into the blood. The circulatory system (heart, blood vessels, blood) carries both oxygen and glucose to every cell in the body and carries CO₂ and other waste away. These three systems are not optional additions — they exist because every one of the body's trillions of cells does respiration and cannot get what it needs on its own.
Every cell needs oxygen and glucose to do cellular respiration (W3). Three systems work together to deliver both: the respiratory system brings in oxygen; the digestive system provides glucose from food; the circulatory system carries both to every cell. They also remove waste. These systems must be coordinated — not independent.
Worked example — tracing oxygen from air to a muscle cell (watch how an expert reasons)
1. Air enters: You breathe in through your nose/mouth → trachea → bronchi → lungs.
2. Gas exchange at alveoli: Oxygen crosses from the air sacs into the blood (thin alveolar walls = large surface area = rapid diffusion). CO₂ crosses the other way to be exhaled.
3. Transport in blood: O₂ binds to hemoglobin in red blood cells → heart pumps blood → arteries carry it outward → capillaries (tiny vessels) reach every cell in the body.
4. Delivery to muscle cell: O₂ diffuses from the capillary into the muscle cell → enters the mitochondria.
5. Cellular respiration: Glucose + O₂ → CO₂ + water + ATP. The muscle cell uses ATP to contract.
6. Waste removal: CO₂ diffuses back into the blood → veins carry it to the heart → heart pumps it to the lungs → exhaled.
Every step in this chain is a different level of organization doing its structural job.
Show me the levels graphic organizer Tier 2 · organizer
Fill in the blank cells using this word bank: circulatory · respiratory · digestive · oxygen · glucose · CO₂ · tissue · organ · coordinated · independent · red blood cells · cellular respiration · levels of organization · heart · lungs · muscle cell · neuron
| Level | Definition | Your example |
|---|---|---|
| Cell | Basic unit of life | _______ |
| Tissue | Similar cells doing the same job | muscle _______ |
| Organ | Different tissues working together | _______ (pumps blood) |
| Organ system | Organs working together for one function | _______ system (delivers O₂) |
| Organism | All systems working together | you |
Then use these sentence frames for the CER:
Claim: The body delivers matter and energy to all its cells through ________.
Evidence: For example, the ________ system provides ________ by ________, and the ________ system delivers it to cells by ________.
Reasoning: This works because the systems are ________, not ________.
Your turn Explain the phenomenon
Use a Claim–Evidence–Reasoning model to answer: How does the body get matter and energy to every one of its trillions of cells? Connect to the paper-cut phenomenon and to cellular respiration from Week 3. Choose how you respond — all are equally valid.
The task: Make a claim about how the body delivers matter and energy to all its cells, give evidence from the oxygen-delivery trace we built, and explain your reasoning connecting levels of organization to cellular respiration. Use the phrase "structure and function" at least once.
I want sentence starters Tier 2 · frames
Claim: The body delivers oxygen and glucose to all its cells through a coordinated system of ________.
Evidence: The ________ system (lungs + airways) brings oxygen into the body, and the ________ system (heart + blood vessels) delivers it through ________ (cells) to every cell. The ________ system provides glucose from digested food. Together, these systems supply what every cell needs for ________ (the process from W3).
Reasoning: This works because the systems are ________, not _______. No single cell, tissue, or organ can deliver oxygen and glucose to 37 trillion cells on its own — it takes the whole ________ of organization working together.
Word bank: circulatory · respiratory · digestive · red blood cells · cellular respiration · levels · coordinated · independent · oxygen · glucose · CO₂ · ATP · tissue · organ · organ system
Let's make it concrete first Tier 3 · re-teach
The school-building analogy: A school is a system. Individual students (cells) → classrooms (tissues — cells of the same type together) → departments (organs — classrooms working toward the same goal) → the school (organ system) → the district (organism). The cafeteria (digestive system), the HVAC (respiratory system), and the hallways (circulatory system) work together to deliver what every classroom needs. No classroom independently runs its own cafeteria. The school is the system. Your body works the same way.
Fill in using the analogy: In the school analogy, students = ________, classrooms = ________, departments = ________, and the hallways that deliver food and air = the ________ system in the body.
Now connect back: every cell in your body does ________ (from W3), which needs ________ and ________. The organ systems ________ (work together / work alone) to deliver these.
Push my thinking Extension
Research how cancer cells evade the body's coordination systems. How do tumors manage their own blood supply (angiogenesis)? Connect: tumors break the structure-function organization of healthy tissue. Explain using the levels of organization why a tumor that disrupts a single organ can eventually affect the whole organism.
Check yourself Did it click?
- list the five levels of organization from cell to organism and give one example at each level;
- explain that structure determines function at every level, with at least one example;
- describe how the respiratory, digestive, and circulatory systems work as a coordinated delivery system for all cells;
- connect the delivery system to cellular respiration from Week 3 — every cell needs oxygen and glucose to make ATP.
Which statement BEST explains how a living body delivers matter and energy to all its cells?
Re-teach: organ coordination and cell differentiation Tier 3
Misconception 1 — Organs work independently: Draw the oxygen delivery chain mentally: lungs cannot work without the heart (it has no pump to move oxygen-rich blood), and the heart cannot work without blood vessels (there is no path to deliver blood to remote cells). They are a system, not independent neighbors. The circulatory system reaches cells in your fingertips and your brain — organs far from both the heart and lungs — because the system is a connected network.
Misconception 2 — All cells are identical: Look at the diagram. A red blood cell is a biconcave disc — no nucleus, filled with hemoglobin — perfectly shaped to carry oxygen. A neuron has long branching extensions to send electrical signals across your body. A skin cell is flat and tightly packed to form a barrier. Each different structure enables a different function. Cells differentiate during development, giving each type a unique structure matched to its unique job.
Complete this: The three systems that work together to deliver matter and energy to cells are the ________ system (oxygen), the ________ system (glucose), and the ________ system (delivery). They must be ________ (coordinated / independent) because no single organ can supply all ________ trillion cells alone.
Reflect, then show what you know
Reflection metacognition + SEL
Which support did you use today (if any), and did it help? There is no wrong answer. Also: did feeling your own heartbeat during the brain break make the levels of organization feel more real? Notice how you learn — that awareness is itself a scientific skill.
Exit ticket — answer on paper or in your notebook.
- New List the five levels of organization from smallest to largest. Give one example at each level from the human body.
- New A red blood cell is disc-shaped and flexible. A neuron is long and branching. Explain how the different structures of these two cells relate to their different functions. Use the phrase "structure and function."
- Spiral Your muscle cells need oxygen and glucose to do cellular respiration. Name the two organ systems that deliver each of those materials to the muscle cells, and describe what each system does.
- Spiral The glucose delivered to your cells was once CO₂ in the air. Trace the matter: how did carbon atoms get from the atmosphere into your bloodstream? Name at least two steps.
- Transfer You are about to model how a living thing — the windowsill plant — stays alive. What three things does it need to take in, and what does it do with each one? This is the core of your Week 5 task.
Educator panel — facilitation, accommodations, answer key
At a glance
Standard: NGSS MS-LS1-3 (use argument supported by evidence for how the body is a system of interacting subsystems composed of groups of cells). 3D: SEP Developing & Using Models · DCI LS1.A Structure & Function · CCC Systems & System Models and Scale, Proportion & Quantity. Throughline: every lesson in Unit 5 has been building to this: cells → tissues → organs → systems → organism, all unified by the need to support cellular respiration in every cell. This lesson makes that architecture explicit and gives students the vocabulary to explain it.
Materials (fully digital-capable): student notebook; optional — slides or wall diagram showing levels of organization. No lab required. A pulse oximeter (common in many households post-2020) is a compelling optional demo — it measures both heart rate and blood oxygen at once, making the circulatory-respiratory link tangible.
Facilitation arc (Rosenshine)
- Launch phenomenon — paper-cut image, notice/wonder before vocabulary (3 min).
- Do-Now retrieval — cellular respiration (W3), photosynthesis carbon source (W2), organelles (W1) (3 min).
- Build Steps 1–3 with worked example: levels → structure/function → delivery system → oxygen-trace (12 min). Cold-call after each step: "What is one example of structure matching function at this level?"
- Differentiated CER — explaining matter/energy delivery to all cells; circulate; name tier supports (15 min).
- Self-check + re-teach branch for A/C responders; address both misconceptions explicitly (5 min).
- Brain break — pulse felt on chest, count 5 beats; makes circulatory system real (2 min).
- Reflection + exit ticket; item 5 primes W5 performance task (10 min).
IEP / 504 accommodation cards
Common accommodations mapped to this lesson
| Accommodation | How it is already built in / what to do |
|---|---|
| Text read aloud | Every passage has a Listen button (TTS); the simplified toggle shortens it. |
| Reduced reading load | "Reading: Simplified" swaps in shorter plain-language text site-wide. |
| Chunking / extended time | Lesson is in small steps with checks; progress saves automatically. |
| Sentence frames / word bank | Tier-2 panel provides graphic organizer, sentence frames, and word bank. |
| Concrete / analogical support | Tier-3 school-building analogy maps abstract organ-system coordination onto a familiar environment. |
| Alternative response mode | Students may draw the oxygen-delivery chain, record, or write the CER — all accepted. |
| Behavior / focus (504, ADHD) | Named expectations (PBIS), 30-sec check-in, and a sensory brain break (feeling own heartbeat). |
| Multilingual / EL | Simplified text, labeled SVG at five levels, word bank; graphic organizer bridges vocabulary. |
Exit ticket answer key
- Cell (e.g., red blood cell) → tissue (e.g., muscle tissue) → organ (e.g., heart) → organ system (e.g., circulatory system) → organism (e.g., human). Any valid, anatomically consistent examples are accepted.
- Structure and function: a red blood cell's biconcave disc shape maximizes surface area for oxygen binding to hemoglobin; a neuron's long branching shape allows it to transmit electrical signals across long distances in the body. Different structures = different functions.
- Oxygen is delivered by the respiratory system (lungs bring O₂ into the blood) and the circulatory system (heart + blood vessels carry O₂-carrying red blood cells to muscle cells). Glucose is absorbed by the digestive system and delivered via the circulatory system.
- Carbon as CO₂ in air → absorbed into a plant leaf through stomata → fixed into glucose during photosynthesis → plant glucose eaten as food → digested into glucose → absorbed into bloodstream. (Multiple valid paths; any two steps earn credit.)
- Accept: the plant needs CO₂ (for photosynthesis → glucose), water (for photosynthesis and cell structure), and sunlight (energy source for photosynthesis). It also needs to take in O₂ for cellular respiration. Full credit for three things with correct use; partial credit if the student confuses photosynthesis and respiration directions. This item directly primes W5's performance task — do not over-correct; let the student's current model surface.
Why it is designed this way
The paper-cut phenomenon is chosen deliberately: it makes visible all five levels of organization simultaneously (a cell is damaged, tissues respond, the organ seals, the integumentary system coordinates, and the organism heals). Phenomenon-first before vocabulary (NRC 2012). The oxygen-delivery trace is a worked example using an expert's chain of reasoning — it models how to connect levels of organization through a single continuous story rather than as isolated facts (Sweller, cognitive load). The two-misconception self-check targets the most common errors for this standard (AAAS Project 2061): independent organs and identical cells. The school-building Tier-3 analogy uses a students' own lived environment as a cognitive bridge. Exit ticket item 5 is an explicit advance organizer for W5 (Ausubel): students commit a prediction to paper, which primes schema retrieval next lesson and reduces W5 cognitive load.