Chapter 1 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

S3.1.1 Chapter 1

Signs of life

How can I tell whether something is alive?

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

  • List the life processes shared by all living things
  • Use the life processes to decide if a seed or fire is alive

Think of a dog, a tree and a stone. The dog and the tree are alive. The stone is not. How do you know?

Scientists look for seven signs. Each one is a job that a living thing does. We call each job a life process. A living thing shows all seven during its life.

Draw it first

Draw a plant growing

  1. Three pictures of a plant in soil, one after another, each taller than the one before. The first shows a seed, the second a young plant and the third a grown plant. Labels: seed, young plant, grown plant.seed

    1 Draw a seed lying in the soil.

  2. Three pictures of a plant in soil, one after another, each taller than the one before. The first shows a seed, the second a young plant and the third a grown plant. Labels: seed, young plant, grown plant.seedyoung plant

    2 Draw the same plant later. It is a young plant now, and taller.

  3. Three pictures of a plant in soil, one after another, each taller than the one before. The first shows a seed, the second a young plant and the third a grown plant. Labels: seed, young plant, grown plant.seedyoung plantgrown plant

    3 Draw it later still. It has grown a lot. Growing is the first sign of life.

The seven signs are in the table. You can remember them with the first letters: M R S G R E N.

A table of the seven life processes and what each one means. Movement: moves. Respiration: gets energy. Sensitivity: notices things. Growth: gets bigger. Reproduction: makes young. Excretion: removes waste. Nutrition: takes in food. Labels: process, what it does, movement, respiration, sensitivity, growth, reproduction, excretion, nutrition, moves, gets energy, notices things, gets bigger, makes young, removes waste, takes in food.processwhat it doesmovementmovesrespirationgets energysensitivitynotices thingsgrowthgets biggerreproductionmakes youngexcretionremoves wastenutritiontakes in food
The seven life processes.

Animals move their whole body. Plants move too, but slowly. A plant turns its leaves to the light, and its roots grow down. Moving is only one sign. Wind moves a leaf, and that leaf is not alive because of it.

Sensitivity means noticing a change and reacting to it. You pull your hand back from a hot pan. A plant grows toward light.

Nutrition means taking in food. Animals eat. Plants make their own food from light, air and water.

A food chain of three boxes joined by arrows that read eaten by: plant, goat, person. It shows that animals get their food from plants, or from animals that ate plants. Labels: plant, goat, person, eaten by.plantgoatpersoneaten byeaten by
Nutrition: a plant makes food. A goat and a person eat.

Respiration is not the same as breathing. Breathing brings air into your body. Respiration happens in every cell. It releases energy from food, using oxygen. Carbon dioxide and water are made too.

Excretion means getting rid of waste that the body makes. You breathe out carbon dioxide and you pass water and other waste. Reproduction means making young of the same kind.

See it three ways

With things

Run on the spot for a minute. You feel warm and you breathe faster. Your cells are releasing more energy from food.

As a picture

Two boxes joined by an arrow. The first box says food and oxygen. The second box says energy, CO₂ and water. It shows what respiration does in a cell. Labels: food and oxygen, energy, CO₂ and water.food and oxygenenergy, CO₂ and water

In words

Respiration uses food and oxygen. It releases energy. It makes carbon dioxide and water. It happens in every living cell, all day.

Now test two puzzling things. A candle flame moves, grows, and uses up air and wax. But it makes no young of its own. It cannot notice or react as a living thing does. Most of all, a fire is not made of cells. Every living thing is. So it is not alive.

A dry seed does not seem to move, grow or feed. But it is alive. It is resting. It respires very slowly. Give it water and warmth and it grows.

A person, a seed in soil and a candle, side by side. Under each is a word. The person is alive. The seed is alive but resting. The candle is not alive. Labels: person, seed, candle, alive, alive and resting, not alive.personaliveseedalive and restingcandlenot alive
Some things need a careful look.

Try it

Wake a resting seed

You need: 3 dry bean seeds, or peas or maize, a cloth or paper, a clean jar, water, a ruler.

Be safe: Do not eat the seeds. Raw beans can make you ill. Wash your hands when you finish. If mould grows, do not open the jar near your face or sniff it. Throw it away and wash your hands.

  1. Wet the cloth. Squeeze it so it is damp, not dripping. Put it in the jar.
  2. Put the seeds between the cloth and the glass, where you can see them. Keep the jar somewhere warm.
  3. Look every day for five days. Keep the cloth damp. Measure the root with the ruler and write it down.

What you will see: The seeds lay still for a day or two. Then a root came out and grew longer each day. The dry seed was alive and resting all the time.

If you cannot try it, this is what happens.
A line graph of root length in millimetres against the day, from day 0 to day 5. The root is 0 mm on day 0 and day 1, then grows to 27 mm on day 5. Labels: day, root length in mm, 0, 1, 2, 3, 4, 5, 0, 10, 20, 30.0102030012345dayroot length in mm

A wrong idea many people have

Anything that moves is alive.

Why it feels right: Animals move all the time, so moving seems to mean life.

The test that breaks it: A river flows, a cloud drifts and a car rolls. None of them is alive. A tree does not walk anywhere, and it is alive.

What is true: Moving is one of seven signs. A living thing shows all seven during its life.

Key words

life process
a job that every living thing does, such as growing.
respiration
releasing energy from food inside cells. It is not the same as breathing.
sensitivity
noticing a change and reacting to it.
excretion
getting rid of waste that the body makes.
nutrition
taking in food, or making it, as plants do.
reproduction
making young of the same kind.

Back to your guess

The answer is C: A living thing does several jobs, such as grow, feed and make young.

Moving is only one sign. A living thing shows seven signs in all. A plant shows every one of them, though often more slowly than an animal.

Check yourself

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

  1. Which of these is not one of the seven life processes?

    Tap your answer.

    1. Not this one. Growth is a life process. Even a tree grows, though slowly. You may think only animals grow. Go to S3.1.1. Try another.

    2. Not this one. Excretion, getting rid of waste, is a life process. You may be thinking of it as something only animals do. Go to S3.1.1. Try another.

    3. Yes, that is right. Many living things, such as plants, make no sound at all. The seven are movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.

    4. Not this one. Reproduction, making young, is a life process. You may think it only means having babies, but plants do it too. Go to S3.1.1. Try another.

    See the answer

    Making a noise

    Many living things, such as plants, make no sound at all. The seven are movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.

    • If you chose A: Growth is a life process. Even a tree grows, though slowly. You may think only animals grow. Go to S3.1.1.
    • If you chose B: Excretion, getting rid of waste, is a life process. You may be thinking of it as something only animals do. Go to S3.1.1.
    • If you chose D: Reproduction, making young, is a life process. You may think it only means having babies, but plants do it too. Go to S3.1.1.

  2. What is respiration?

    Tap your answer.

    1. Not this one. Breathing is not respiration. Breathing brings air to your body. Respiration happens inside cells. Go to S3.1.1. Try another.

    2. Yes, that is right. Cells use oxygen to release energy from food. Breathing only brings the air in.

    3. Not this one. That is excretion. Respiration is the release of energy from food. Go to S3.1.1. Try another.

    See the answer

    Releasing energy from food inside cells.

    Cells use oxygen to release energy from food. Breathing only brings the air in.

    • If you chose A: Breathing is not respiration. Breathing brings air to your body. Respiration happens inside cells. Go to S3.1.1.
    • If you chose C: That is excretion. Respiration is the release of energy from food. Go to S3.1.1.

  3. A dry seed lay in a jar for a year. Then it grew when it was wet. What was it during the year?

    Tap your answer.

    1. Not this one. A thing that is not alive cannot become alive. The seed was alive all the time, only resting. Go to S3.1.1. Try another.

    2. Yes, that is right. The seed respired very slowly all year. With water and warmth it started to grow.

    3. Not this one. Moving is only one sign of life. A plant seed does not move, and it is alive. Go to S3.1.1. Try another.

    See the answer

    Alive, but resting.

    The seed respired very slowly all year. With water and warmth it started to grow.

    • If you chose A: A thing that is not alive cannot become alive. The seed was alive all the time, only resting. Go to S3.1.1.
    • If you chose C: Moving is only one sign of life. A plant seed does not move, and it is alive. Go to S3.1.1.

  4. A fire moves, grows and uses up air. Why is it not alive?

    Tap your answer.

    1. Yes, that is right. A fire makes no young of its own. It does not notice and react as a living thing does. Most of all, it is not made of cells, and every living thing is.

    2. Not this one. Heat is not the test. Some living things are warm and some are cold. Look at the seven signs. Go to S3.1.1. Try another.

    3. Not this one. Moving and growing are only two signs. A living thing shows all seven. Go to S3.1.1. Try another.

    See the answer

    It does not show all seven signs, and it is not made of cells.

    A fire makes no young of its own. It does not notice and react as a living thing does. Most of all, it is not made of cells, and every living thing is.

    • If you chose B: Heat is not the test. Some living things are warm and some are cold. Look at the seven signs. Go to S3.1.1.
    • If you chose C: Moving and growing are only two signs. A living thing shows all seven. Go to S3.1.1.

  5. A tree does not walk about. Why do we say it is alive?

    Tap your answer.

    1. Not this one. Colour does not make a thing alive. Many living things are not green. Go to S3.1.1. Try another.

    2. Not this one. A stone can lie in soil too. We look at what the thing does, not where it is. Go to S3.1.1. Try another.

    3. Yes, that is right. A tree grows, makes food, notices light, makes seeds, and moves its leaves and roots slowly.

    See the answer

    It shows all seven life processes, but slowly.

    A tree grows, makes food, notices light, makes seeds, and moves its leaves and roots slowly.

    • If you chose A: Colour does not make a thing alive. Many living things are not green. Go to S3.1.1.
    • If you chose B: A stone can lie in soil too. We look at what the thing does, not where it is. Go to S3.1.1.

  6. The root of a seed measures 4 mm on day 2 and 27 mm on day 5. How many millimetres did it grow?

    See the answer

    23 mm

    Take the first length from the second length. 27 − 4 = 23.

Keep it

Copy this into your exercise book.

Every living thing shows seven signs: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. A fire shows some, but it is not made of cells, so it is not alive. A dry seed is alive and resting.

Draw: Draw a seed, a young plant and a grown plant in a row, and write growth under them.

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.