---
title: "Why are cells different shapes?"
subtitle: "Year 8 Biology · From cells to organs · Lesson 5"
---

# Why are cells different shapes?

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

> **Key question:** A nerve cell in your leg can be a metre long. A red blood cell is a tiny squashed disc with no nucleus. Same DNA, same body. Why so different?


:::teacher-note

**In one sentence:** Students explain that cells with the same DNA specialise, and describe how structural features of specialised cells serve their functions (AC9S8U02, node 1, a hinge node).

**Students should be able to say:** I can describe two features of a specialised cell and explain how each helps. I can explain that cells with the same DNA can specialise for different jobs. I can link a cell's contents (such as mitochondria) to its job.

**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.

:::


## Engage


:::keep-together

**A nerve cell and a muscle cell from the same person. How do you predict their DNA compares?**

☐ The same DNA, but each cell uses different parts of it

☐ Only nerve cells have DNA

☐ Completely different DNA

☐ Muscle cells have more DNA

My prediction, and why:

{{lines-3}}

:::


:::teacher-note

**What happens:** The same DNA. Each cell switches on the instructions it needs, so it grows the shape and parts that suit its job.

:::


## Explore

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

{{lines-2}}

## Explain: shape suits job


:::keep-together

### Feature and function

**Match each feature to how it helps.**

A. Carries signals a long way

B. Large surface for absorbing water

C. Releases lots of energy for contracting

D. More room for haemoglobin to carry oxygen

{{columns 60% 40%}}

{{rows 1}}

| Part | Letter |
|---|---|
| `Red blood cell: no nucleus` | |
| `Nerve cell: long axon` | |
| `Muscle cell: many mitochondria` | |
| `Root hair cell: long extension` | |

:::


:::teacher-note

**Answer:** Red blood cell: no nucleus → D. More room for haemoglobin to carry oxygen; Nerve cell: long axon → A. Carries signals a long way; Muscle cell: many mitochondria → C. Releases lots of energy for contracting; Root hair cell: long extension → B. Large surface for absorbing water

:::


:::keep-together

### Root hairs

**Why do root hair cells have no chloroplasts?**

☐ They are underground, where there is no light for photosynthesis

☐ Roots take in their food from the soil, so they don't need to make any

☐ Only leaves are allowed chloroplasts

:::


:::teacher-note

**Answer:** They are underground, where there is no light for photosynthesis

:::


:::keep-together

### Specialised

**What does 'specialised' mean for a cell?**

☐ It has different DNA

☐ Its shape and parts suit one particular job

☐ It is bigger than other cells

:::


:::teacher-note

**Answer:** Its shape and parts suit one particular job

:::


:::typical

## Elaborate: design a cell


:::keep-together

**Cells lining your small intestine absorb digested food. Which feature would you expect them to have?**

☐ A long tail to swim

☐ Tiny folds (microvilli) on the surface, for a much larger area

☐ No membrane, so food gets in easily

:::


:::teacher-note

**Answer:** Tiny folds (microvilli) on the surface, for a much larger area

Like root hairs, intestine cells increase their surface area to absorb more.

:::

:::


:::wider

## Elaborate: energy-hungry cells


:::keep-together

**Sperm cells and muscle cells both have many mitochondria. What do the two jobs have in common?**

☐ Both make proteins

☐ Both store food

☐ Both need lots of energy for movement

:::


:::teacher-note

**Answer:** Both need lots of energy for movement

:::

:::


## Evaluate: look back

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

**Revision summary**

- Nearly all your cells have the **same DNA**; each **specialised** cell uses different instructions.
- A specialised cell's **shape and parts suit its job**: red blood cells (no nucleus, haemoglobin), nerve cells (long axon), muscle cells (many mitochondria), root hair cells (long extension, no chloroplasts).

## Exit ticket

:::keep-together

**Give one feature of a nerve cell and explain how it helps.**

{{lines-3}}

:::


:::teacher-note

**Answer:** A long axon, so it can carry signals a long way through the body.

:::