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# What is an organ made of?

Year 8 Biology · From cells to organs

<!-- Speaker note: Students describe an organ as several tissue types working together and explain each tissue's contribution (AC9S8U02, node 3, a hinge node). About 25 minutes (Engage and Explore 7 min · Explain 9 min · Evaluate 3 min · Typical adds 4 min, Wider about 2 min). -->

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## Today

**We are learning to** an organ is made of several different tissues working together. A leaf has epidermis, palisade and spongy mesophyll and vascular tissue; the heart has cardiac muscle, a lining, connective tissue and nervous tissue.

- I can name two tissues in an organ and explain how each helps.
- I can explain why organs need more than one tissue.
- I can put cells, tissues, organs, systems and organisms in order.

<!-- Speaker note: Before class: A concept tutorial for introducing or revising the idea; it does not replace a leaf section under the microscope or a heart dissection. Set the width with `?width=minimum`, `typical` (default) or `wider`. The hinge risk is organs as one tissue ("the heart is a muscle"). The leaf shows five tissues before the heart appears. Board notes: the leaf is one simplified slice; the heart diagram is a strip of the wall, not the whole heart. -->

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## Why it matters

> A leaf looks like one green sheet. Slice it thinly and look through a microscope, and you find at least five different layers, each doing a different job.

<!-- Speaker note: Cells specialise; similar cells form tissues. This lesson: tissues build organs. -->

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<span style="background:#dbeafe; color:#1a1a1a; border:1.5px solid #3b82f6; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">💬 Discussion</span>

## Engage: predict

**A leaf is an organ. What do you predict it is made of?**

- Chlorophyll and water
- Only veins
- One kind of green cell
- Several different tissues, each with its own job

<!-- Speaker note: What happens: Several different tissues: a protective epidermis, two kinds of mesophyll for photosynthesis and gas exchange, and xylem and phloem for transport. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: 'one kind of green cell' is the misconception to resolve. -->

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<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Explore it

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fbiology-8%2Forgans%2Fstep-2&code=widget%3A+cell%0Ashow%3A+leaf%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/biology-8/organs/?full=step-2#step-2)

<!-- Speaker note:  -->

<!-- Speaker note: Teacher: ask which tissue does photosynthesis and which brings water. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## What happened?

* Several different tissues: a protective epidermis, two kinds of mesophyll for photosynthesis and gas exchange, and xylem and phloem for transport.

<!-- Speaker note: Reveal after running. Ask who predicted it, and what made them think so. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Leaf tissues

**Match each leaf tissue to its job.**

| | |
|---|---|
| `Palisade mesophyll` | A. Brings water from the roots |
| `Spongy mesophyll` | B. Air spaces let gases reach every cell |
| `Xylem` | C. Protects the leaf |
| `Phloem` | D. Carries sugar to the rest of the plant |
| `Epidermis` | E. Most photosynthesis, near the light |

* Answer: Palisade mesophyll → E. Most photosynthesis, near the light; Spongy mesophyll → B. Air spaces let gases reach every cell; Xylem → A. Brings water from the roots; Phloem → D. Carries sugar to the rest of the plant; Epidermis → C. Protects the leaf

<!-- Speaker note:  -->

<!-- Speaker note: Teacher: the 'why several' question is the checkpoint. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Why several

**Why does a leaf need more than one tissue?**

- It doesn't; the extra tissues are spare
- Photosynthesis needs light, water, gas exchange, protection and transport: no single tissue can do all of them
- More tissues make it greener

* Answer: Photosynthesis needs light, water, gas exchange, protection and transport: no single tissue can do all of them

<!-- Speaker note:  -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Levels

**Put the levels of organisation in order, smallest first.**

```science
Organ system
Tissue
Cell
Organ
Organism
```

<!-- Speaker note: Correct order: Cell Tissue Organ Organ system Organism -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## A blocked tissue

**A wilt disease blocks the xylem in a leaf. What happens to the leaf?**

- Nothing much: the other tissues still do their own jobs
- The palisade cells take in water from the air instead
- Its cells run short of water, so photosynthesis slows and the leaf wilts

* Answer: Its cells run short of water, so photosynthesis slows and the leaf wilts

<!-- Speaker note: A change in one tissue changes the whole organ, because its tissues depend on each other. -->

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<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Elaborate: the heart wall

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fbiology-8%2Forgans%2Fstep-4&code=widget%3A+cell%0Ashow%3A+heart%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/biology-8/organs/?full=step-4#step-4)

<!-- Speaker note: What this step is for: A second organ, an animal one, shows the same multi-tissue pattern. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Only muscle?

**If the heart were made only of cardiac muscle, what would go wrong?**

- It would beat too slowly
- Nothing: muscle does it all
- No smooth lining (blood would clot), no valves (blood would flow backwards), no nerves to adjust how fast it beats

* Answer: No smooth lining (blood would clot), no valves (blood would flow backwards), no nerves to adjust how fast it beats

<!-- Speaker note:  -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Elaborate: when a tissue fails

**In atherosclerosis, fatty deposits and thickened tissue build up in artery walls. How does this affect the circulatory system?**

- Arteries narrow, so less blood reaches organs like the heart muscle, which can cause a heart attack
- Arteries get wider and blood flows faster
- It only affects the blood, not the organs

* Answer: Arteries narrow, so less blood reaches organs like the heart muscle, which can cause a heart attack

<!-- Speaker note: What this step is for: Tracing a tissue disorder to organ failure shows why organ function depends on every tissue. -->

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## Evaluate: look back

Write one sentence: "At first I thought… Now I think… because…"

**Revision summary**

- **Cells → tissues → organs → organ systems → organism.**
- A **tissue** is a group of similar cells doing one job; an **organ** is several tissues working together.
- A leaf: epidermis, palisade and spongy mesophyll, xylem and phloem. The heart: cardiac muscle, lining, connective tissue, nervous tissue.
- No single tissue can do everything an organ needs.

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Exit ticket

**Name two tissues in a leaf and say what each does.**

* For example: palisade mesophyll (photosynthesis) and xylem (brings water).

<!-- Speaker note: Students answer on paper or a mini whiteboard before the reveal. Anyone who cannot answer needs the main idea again next lesson. Where this leads: Next: organ systems (node 4). In class: leaf sections under the microscope; a sheep heart dissection. -->