---
title: "What is an organ made of?"
subtitle: "Year 8 Biology · From cells to organs · Lesson 7"
---

# What is an organ made of?

**Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}}

> **Key question:** 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.


:::teacher-note

**In one sentence:** Students describe an organ as several tissue types working together and explain each tissue's contribution (AC9S8U02, node 3, a hinge node).

**Students should be able to say:** 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.

**Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet.

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## Engage


:::keep-together

**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

My prediction, and why:

{{lines-3}}

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:::teacher-note

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

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## Explore

Try it on the board in the tutorial. Was your prediction right? What was different?

{{lines-2}}

## Explain: tissues working together


:::keep-together

### Leaf tissues

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

A. Brings water from the roots

B. Air spaces let gases reach every cell

C. Protects the leaf

D. Carries sugar to the rest of the plant

E. Most photosynthesis, near the light

{{columns 60% 40%}}

{{rows 1}}

| Part | Letter |
|---|---|
| `Palisade mesophyll` | |
| `Spongy mesophyll` | |
| `Xylem` | |
| `Phloem` | |
| `Epidermis` | |

:::


:::teacher-note

**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

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:::keep-together

### 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

:::


:::teacher-note

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

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:::keep-together

### Levels

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

A. `Organ system`

B. `Tissue`

C. `Cell`

D. `Organ`

E. `Organism`

Correct order (letters): {{field-24}}

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:::teacher-note

**Answer:** see the program below

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

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:::keep-together

### 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

:::


:::teacher-note

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

A change in one tissue changes the whole organ, because its tissues depend on each other.

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:::typical

## Elaborate: the heart wall


:::keep-together

### 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

:::


:::teacher-note

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

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:::wider

## Elaborate: when a tissue fails


:::keep-together

**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

:::


:::teacher-note

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

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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.

## Exit ticket

:::keep-together

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

{{lines-3}}

:::


:::teacher-note

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

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