Chapter 5 of 8

All 8 chapters
  1. 1Signs of life, readunderstood
  2. 2Seeing small things, readunderstood
  3. 3Animal and plant cells, readunderstood
  4. 4What each part does, readunderstood
  5. 5Cells with special jobs, readunderstood
  6. 6Cells, tissues and organs, readunderstood
  7. 7Diffusion, readunderstood
  8. 8Living things with one cell, readunderstood

S3.1.5 Chapter 5

Cells with special jobs

Why are some cells long and thin, and others round and flat?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

  • Explain how nerve, red blood and root hair cells suit their jobs
  • Match a special cell to the job it does

Your body has many kinds of cell. A specialised cell has a shape that suits one job. Look at three of them.

First, a nerve cell. Its job is to carry messages from one part of the body to another. A nerve cell draws in three steps.

Draw it first

Draw a nerve cell

  1. A nerve cell drawn in three steps. First a round cell body with a nucleus inside. Then a very long thin fibre goes out to the right. Last, short branches are added at both ends. Labels: nucleus, long fibre, branches.nucleus

    1 Draw a small round cell body with a nucleus inside it.

  2. A nerve cell drawn in three steps. First a round cell body with a nucleus inside. Then a very long thin fibre goes out to the right. Last, short branches are added at both ends. Labels: nucleus, long fibre, branches.nucleuslong fibre

    2 Draw a very long, thin fibre going out from it. This is the part that carries the message.

  3. A nerve cell drawn in three steps. First a round cell body with a nucleus inside. Then a very long thin fibre goes out to the right. Last, short branches are added at both ends. Labels: nucleus, long fibre, branches.nucleuslong fibrebranches

    3 Draw short branches at both ends. They pass the message to the next cell.

A nerve cell can be about a metre long. Some run from your foot up to your back. Its long fibre carries a message a long way. The fastest messages travel about 100 metres every second.

Next, the red blood cell. It carries oxygen round the body in your blood. Its shape is a flat disc with a dent on each side.

A red blood cell seen from above and from the side. From above it is a round hatched disc with a paler, plain middle, which is the dent. From the side it is thick at the edges and thin in the middle. The words say that it has no nucleus. Labels: dented middle, no nucleus, side view.dented middleno nucleusside view
A red blood cell. It has a dented middle and no nucleus.

The flat, dented shape gives a large surface, so oxygen can get in and out quickly. The cell is also small and bendy, so it can squeeze through the thinnest blood tubes. In people and other mammals, a red blood cell has no nucleus. That leaves more room to carry oxygen.

Last, the root hair cell. It grows in the skin of a root, and it takes in water from the soil. It has a long thin hair that reaches between the grains of soil.

Three root cells stacked in a column. The middle one is a root hair cell, with a nucleus. A long thin hair grows out of the same cell to the right, with no wall between them, among small grains of soil. Labels: nucleus, root hair, soil.root hairnucleussoil
A root hair cell. The hair is many times longer than the cell is wide.

The hair gives the cell a much larger surface area. Surface area means how much outside a thing has. More surface means more water can pass in, so the plant gets water faster. A root cell is in the dark soil, so it has no chloroplasts.

See it three ways

With things

Think of a telephone wire. It is long and thin so that it can carry a message far. A nerve cell is made for the same reason.

As a picture

Three special cells, one under another, each drawn small and not to scale, with its name beneath. A nerve cell, long with branches. A red blood cell, a dented disc. A root hair cell, with a long hair. Labels: nerve cell, red blood cell, root hair cell.nerve cellred blood cellroot hair cell

In words

The shape of each cell suits its job. A long thin cell carries messages. A dented disc carries oxygen. A cell with a long hair takes in water. The three are not drawn to scale. A nerve cell can be far longer than the others.

A table matching each special cell with its job. A nerve cell carries messages. A red blood cell carries oxygen. A root hair cell takes in water. Labels: cell, job, nerve, red blood, root hair, carries messages, carries oxygen, takes in water.celljobnervecarries messagesred bloodcarries oxygenroot hairtakes in water
Each cell has one job.

Try it

Pass a message down a line

You need: 4 or more people, a clock or a way to count seconds.

  1. Stand in a line and hold hands. Everyone but the first person closes their eyes.
  2. The first person squeezes the hand of the next. Each person passes the squeeze on as soon as they feel it.
  3. The last person says "yes" aloud. Count how many seconds it takes.
  4. Try again with a longer line. Does it take longer?

What you will see: The squeeze runs down the line, one person after another. A message runs along nerve cells in a similar way, but much faster.

If you cannot try it, this is what happens.
Three boxes joined by arrows, each arrow labelled squeeze. The boxes read first person, next person and last person. It shows a squeeze passing along a line of people. Labels: first person, next person, last person, squeeze.first personnext personlast personsqueezesqueeze

A wrong idea many people have

Every cell has a nucleus.

Why it feels right: Pictures of cells almost always show a nucleus.

The test that breaks it: Look at the red blood cell in the picture. It has a dented middle and no nucleus. Red blood cells in people lose their nucleus as they grow.

What is true: Most cells have a nucleus, but a red blood cell in a mammal has none.

Key words

specialised cell
a cell with a shape that suits one job.
nerve cell
a long thin cell that carries messages.
red blood cell
a dented disc that carries oxygen round the body.
root hair cell
a root cell with a long hair that takes in water.
surface area
how much outside a thing has.

Back to your guess

The answer is A: Each kind of cell has a shape that helps it do its job.

Many cells are built for one job. A long thin cell carries messages. A flat dented disc carries oxygen. A cell with a hair takes in water.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. Why is a nerve cell long and thin, with branches?

    Tap your answer.

    1. Not this one. Nerve cells carry messages. They do not store food. You may be thinking of a different kind of cell. Go to S3.1.5. Try another.

    2. Yes, that is right. The long fibre reaches far, and the branches hand the message to the next cell.

    3. Not this one. That is the job of the red blood cell, which is a small dented disc. Go to S3.1.5. Try another.

    See the answer

    It carries messages a long way and passes them on.

    The long fibre reaches far, and the branches hand the message to the next cell.

    • If you chose A: Nerve cells carry messages. They do not store food. You may be thinking of a different kind of cell. Go to S3.1.5.
    • If you chose C: That is the job of the red blood cell, which is a small dented disc. Go to S3.1.5.

  2. Which feature helps a red blood cell carry oxygen?

    Tap your answer.

    1. Not this one. A long fibre belongs to a nerve cell. A red blood cell is a small disc. Go to S3.1.5. Try another.

    2. Yes, that is right. The large surface lets oxygen get in and out quickly. The small bendy shape squeezes through thin blood tubes.

    3. Not this one. A long hair belongs to a root hair cell. A red blood cell has none. Go to S3.1.5. Try another.

    See the answer

    Its flat, dented shape gives a large surface.

    The large surface lets oxygen get in and out quickly. The small bendy shape squeezes through thin blood tubes.

    • If you chose A: A long fibre belongs to a nerve cell. A red blood cell is a small disc. Go to S3.1.5.
    • If you chose C: A long hair belongs to a root hair cell. A red blood cell has none. Go to S3.1.5.

  3. What does the long hair of a root hair cell do?

    Tap your answer.

    1. Yes, that is right. More surface means more water can pass in. The hair reaches between grains of soil.

    2. Not this one. Carrying messages is the job of nerve cells. A root hair takes in water. Go to S3.1.5. Try another.

    3. Not this one. Making food is the job of the chloroplast. A root has none, because it is in the dark. Go to S3.1.4. Try another.

    See the answer

    It gives a large surface to take in water from the soil.

    More surface means more water can pass in. The hair reaches between grains of soil.

    • If you chose B: Carrying messages is the job of nerve cells. A root hair takes in water. Go to S3.1.5.
    • If you chose C: Making food is the job of the chloroplast. A root has none, because it is in the dark. Go to S3.1.4.

  4. A cell carries oxygen round the body. Which cell is it?

    Tap your answer.

    1. Not this one. A nerve cell carries messages, not oxygen. Go to S3.1.5. Try another.

    2. Not this one. A root hair cell belongs to a plant and takes in water. It is not in blood. Go to S3.1.5. Try another.

    3. Yes, that is right. Red blood cells are carried in the blood, and they carry oxygen.

    See the answer

    A red blood cell

    Red blood cells are carried in the blood, and they carry oxygen.

    • If you chose A: A nerve cell carries messages, not oxygen. Go to S3.1.5.
    • If you chose B: A root hair cell belongs to a plant and takes in water. It is not in blood. Go to S3.1.5.

  5. Which cell takes in water from the soil for a plant?

    Tap your answer.

    1. Yes, that is right. Its long hair gives a large surface, and it grows in the soil where the water is.

    2. Not this one. A nerve cell is in an animal and carries messages. A plant has no nerve cells. Go to S3.1.5. Try another.

    3. Not this one. A red blood cell is in blood and carries oxygen. A plant has none. Go to S3.1.5. Try another.

    See the answer

    A root hair cell

    Its long hair gives a large surface, and it grows in the soil where the water is.

    • If you chose B: A nerve cell is in an animal and carries messages. A plant has no nerve cells. Go to S3.1.5.
    • If you chose C: A red blood cell is in blood and carries oxygen. A plant has none. Go to S3.1.5.

  6. From an earlier chapter

    Which cell part uses light to make food?

    Tap your answer.

    1. Not this one. The nucleus controls the cell. It does not use light. Go to S3.1.4. Try another.

    2. Not this one. The vacuole holds watery liquid. It makes no food. Go to S3.1.3. Try another.

    3. Yes, that is right. A chloroplast catches light and uses it, with water and carbon dioxide, to make food.

    See the answer

    The chloroplast

    A chloroplast catches light and uses it, with water and carbon dioxide, to make food.

    • If you chose A: The nucleus controls the cell. It does not use light. Go to S3.1.4.
    • If you chose B: The vacuole holds watery liquid. It makes no food. Go to S3.1.3.

  7. A red blood cell is 0.008 mm wide. How many fit side by side along a line 1 mm long?

    See the answer

    125 cells

    Divide the length of the line by the width of one cell. 1 ÷ 0.008 = 125.

Keep it

Copy this into your exercise book.

A nerve cell is long and branched, to carry messages. A red blood cell is a dented disc, to carry oxygen. A root hair cell has a long hair, to take in water.

Draw: Draw a nerve cell, a red blood cell and a root hair cell. Write each cell's job beside it.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

No internet tomorrow? Save the whole book as one file (754 KB). It opens on any phone.