K327 / K328 / 2027

Lesson 6 of 6 / Cell structure and organisation

How specialised cells do their jobs

How does a structure make a cell better at its function?

I can explain adaptations of root hair cells, muscle cells and mature mammalian red blood cells.

  • I can explain specialised cell adaptations.Syllabus

    Syllabus K327 / K328, Topic 1(d). Explain specialised cell adaptations.

About 5 min

Make a guess. You are not marked.

A mature red blood cell in your body has no nucleus. What would you expect this to do?

  1. Stop the cell from working, so it dies at once.
  2. Make the cell heavier so it sinks in the blood.
  3. Leave more room inside the cell for haemoglobin.
Show the answer

Leave more room inside the cell for haemoglobin.

Without a nucleus, more of the cell is filled with haemoglobin, so each cell can carry more oxygen.

The key idea

An adaptation answer needs a chain: a named structure, the advantage it provides and the function that benefits.

Specialised cells have features that help them perform particular functions. Compare the three cells and look for a structure that changes how well the cell does its job.

Explore the idea

Follow structure to function

Root hair cell adaptationLong, narrow extension provides more membrane surface in contact with soil water, supporting greater absorption of water and mineral ions.More absorbing surface
  1. Structure: Long, narrow extension
  2. Benefit: More membrane surface in contact with soil water
  3. Function: Greater absorption of water and mineral ions

Original simplified diagrams, not to scale. The pale centre of the red blood cell shows its thinner region; it is not a nucleus or a hole.

Explanation

A root hair cell has a long, narrow extension into the soil. This increases the surface area of its cell membrane in contact with soil water, allowing greater absorption of water and mineral ions. The extension changes the available absorbing area; it does not give the cell a pump for water.

Muscle cells contain contractile structures and often many mitochondria. Aerobic respiration in the mitochondria releases energy needed for contraction. Cells that contract repeatedly require a continuing energy supply, so the number of mitochondria is linked to the demand of their work.

A mature mammalian red blood cell has no nucleus, leaving more space for haemoglobin, the protein that carries oxygen. Its biconcave shape provides a large surface area relative to its volume and a short diffusion distance for oxygen. It is flexible, helping it pass through narrow capillaries.

Listing a feature is not yet an explanation. "Many mitochondria" becomes an explanation when linked to more aerobic respiration and energy for contraction. The same structure can support different jobs in different cells, so finish with the function of the cell in the question.

Step by step
  1. 1

    Name the job

    For example, a muscle cell contracts; a red blood cell transports oxygen.

  2. 2

    Choose a relevant structure

    Select mitochondria for energy supply or lack of a nucleus for more haemoglobin space.

  3. 3

    Explain the benefit

    Link increased surface area, space or energy supply to the named job.

Worked example

Comparing two muscle samples

Two equally sized muscle cell samples have different numbers of mitochondria. Sample A contracts repeatedly for longer periods. Suggest why A has more mitochondria.

One way to explain it

Repeated contraction requires a sustained supply of energy. More mitochondria allow greater capacity for aerobic respiration, releasing energy for contraction when oxygen and respiratory substrates are available.

Why this answer works
  • Identify the greater demand for contraction.
  • Connect mitochondria with aerobic respiration.
  • Explain energy supply without saying that mitochondria create energy.

Watch out for this

A student says: "A root hair absorbs more because it has a larger volume." What is wrong with this?

Show the answer

Its long projection increases the membrane surface area in contact with the soil. The relevant advantage is more surface for absorption, not simply a larger volume.

Check your understanding

Why does a mature mammalian red blood cell lack a nucleus?

  1. So that it has more room for mitochondria to release energy.
  2. So that it can photosynthesise faster.
  3. To leave more space for haemoglobin to carry oxygen.
Show the answer

To leave more space for haemoglobin to carry oxygen.

Connect the missing nucleus to additional space for haemoglobin, then to oxygen transport.

Exam-style questions

Check your understanding

Which feature of a root hair cell most directly increases the rate of water uptake?

  1. A long extension that gives a large surface area
  2. Many chloroplasts that release energy for osmosis
  3. A thick waxy layer that stops water from leaking out
  4. No cell membrane, so that water can enter freely
Show the answer

A long extension that gives a large surface area

A larger surface area in contact with soil water gives more water uptake per second.

Quick recall

Card 1 of 3. Answer in your head, then check.

How does a structure make a cell better at its function?

You can return to this lesson any time.