Websink Prep UKKS2 ScienceYear 3 chaptersScience textbooksYear 1Year 2Year 3Year 4Year 5Year 6Year 7Year 8Year 9Browse allPast papersFind a tutorBecome a tutor
Primary Science · Year 3Chapter 3 · What plants need
Year 3 · Chapter 3

What plants need

By the end of this chapter you will be able to

  • Name the five things a plant needs: air, light, water, nutrients from the soil and room to grow
  • Say what leaves use light and air for, and why a plant in the dark grows weakly
  • Say that roots take in water and nutrients from the soil, and that nutrients are not food
  • Explain why crowded plants may grow less well, and how plants differ in what they need
  • Describe how water travels up the stem through tiny tubes, and use a table to measure its movement
  • Plan and read a fair test on what a plant needs, and show the results in a table and a bar chart

You should already know

  • Plants need water, light and a suitable temperature to grow (Year 2 Science, Chapter 6)
  • Parts of a flowering plant: roots, stem, leaves and flower (Year 3 Science, Chapter 2)

Where this leads

  • The life cycle of a flowering plant, including pollination and seed dispersal (Year 3 Science, Chapter 4)
  • Fair tests and measuring with a ruler (Year 3 Science, Chapter 1)

National Curriculum for England, Key Stage 2 science, Year 3. Content: P2 explore the requirements of plants for life and growth (air, light, water, nutrients from soil, and room to grow) and how they vary from plant to plant, P3 investigate the way in which water is transported within plants.

Exercise P  Do you remember?

1
FA class grows two bean plants in the same kind of pot, and gives one of them extra water. What is the one thing that changes? Write one word.
2
FWhich part of a plant holds the leaves up towards the light? Write the part.
3
FWhich part of a flowering plant makes seeds? Write the part.
4
FPriya says a bean seed needs water and warmth to start growing. Is she right? Write yes or no.
5
FWhich part of a flowering plant grows out from the stem, and is often broad and flat? Write the part.
3.1

What plants need

Year 3
Explore the requirements of plants for life and growth: air, light, water, nutrients from the soil and room to grow
Video lesson: What plants needComing soon
Story. Class 3C plants bean seeds in pots, and makes a list of what each plant will need. Amira says, “Plants need food, like us.” Mr Patel smiles. “Plants make their own food, but they still need some things from around them.”

A plant is a living thing, and like all living things it needs certain things in order to live and grow. A plant gets these things from its surroundings. It needs five things:

Nutrients are substances in the soil that a plant needs to grow well. The roots take them in with the water.

A plant makes its own food in its leaves. Plants do not eat food like we do. They still need all five things, so that they can make food, grow and stay healthy.

lightroom to growairwaternutrients
A bean plant and the five things it needs: air, light, water, nutrients from the soil and room to grow.

Key ideas

  • A plant needs air, light, water, nutrients from the soil and room to grow.
  • Nutrients are substances in the soil that help a plant to grow well.
  • A plant makes its own food in its leaves.
  • A plant needs all five things to grow and stay healthy.
Worked example 3.1.1
Ali says a plant needs sweets to grow. Is Ali right? Write yes or no.

Method. Think about what a plant gets from its surroundings.

  1. Read the claim. Ali says a plant needs sweets.
    sweets
  2. Check the five needs. The five needs are air, light, water, nutrients from the soil and room to grow. Sweets are not one of them.
    not on the list
  3. Decide. So Ali is not right.
    no
  4. Write the answer.
    no

Check. A plant makes its own food in its leaves, so it does not need sweets. ✓

Watch out. Plants make their own food. Nutrients from the soil are not food.

Worked example 3.1.2
This list has six things: air, light, a television, water, room to grow and nutrients from soil. How many of them does a plant need?

Method. Count only the things a plant needs.

  1. Read the list. The list has six things in it.
    six things
  2. Take out the one that is not a need. A television is not a need of a plant, so take it out.
    a television is out
  3. Count what is left. Five things are left: the five needs of a plant.
    5 needs
  4. Write the answer.
    5

Check. Air, light, water, nutrients and room to grow make five. ✓

Worked example 3.1.3
A bean seed is planted in a pot with plenty of room, light, air and water, but with no soil. Which one of the five needs is missing? Write the need.

Method. Check each need against the pot.

  1. Check the pot. The pot has room, light, air and water.
    room, light, air, water
  2. Find what is not there. The pot has no soil, so nutrients from the soil cannot be taken in.
    no soil
  3. Name the need. The need that is missing is the nutrients from the soil.
    nutrients from soil
  4. Write the answer.
    nutrients from soil

Check. The soil is where a plant takes in its nutrients. ✓

Watch out. Light and water are not missing here. The soil is the thing that is missing.

Watch out

Watch out: a plant does not need to eat food like an animal. It makes its own food in its leaves, using light. But it still needs nutrients from the soil to grow well.

Try it at home or school (with a grown-up). Look at a houseplant or a plant in a garden with a grown-up. Do not pick or pull the plant. Say out loud what you think it needs to live and grow, and check your ideas against the list of five needs. Wash your hands afterwards.

Exam tip

Grown-up tip. Ask: “What does this plant need? Where does it get it from?” Let your child name the five needs, and then point to where each one comes from on the plant.

Exercise 3A  What plants need

1
FName the five things a plant needs to grow. Accept any order.
2
FWhich of these is a need of plants: air or a television? Write the one.
3
FWhat are the substances in soil that help a plant to grow well? Write the word.
4
FFill in the gaps.
(a)A plant makes its own ___ in its leaves.
(b)Plants need ___ to make food, and it comes from the sun.
5
FWhich two needs of a plant come from the soil? Write two words.
6
FLook at the picture. Which need is shown by the sun? Write the need.
lightroom to growairwaternutrients
7
PSSam grows a bean plant in a pot on a crowded shelf, with five other pots pressed against it. The plant has soil, light and water. Which need may be short? Write the need.
8
PSMo sets up 3 pots on a sunny windowsill and 4 pots in a dark cupboard. How many pots are there in all?
9
PSWorking scientifically. Predict: a bean plant has been kept in the dark for two weeks. Write one thing you predict will happen to its leaves.
10
RMaya says a plant does not need air because it is green. Is Maya right? Write no, and give one reason.
11
RA pot has no soil, but it has light, air, water and plenty of room. Explain in one sentence why a plant in this pot may not grow well for long.
3.2

Light and air: making food in the leaves

Year 3
Explore the requirements of plants for life and growth: light and air, and how leaves use them to make food
Video lesson: Light and air: making food in the leavesComing soon
Story. Chloe holds a bean leaf up to the classroom window. “Why does the leaf need light?” she asks. Kofi points to the leaf. “And it gets air through little holes, doesn’t it?”

Plants need light to make food. Leaves catch light, and they use it, together with water and a gas from the air, to make food for the plant.

The gas from the air is called carbon dioxide. Leaves take it in through tiny holes, which are mostly on the underside of the leaf. Plants also give out oxygen, which is a gas that people breathe in.

A plant in a dark place cannot make food from light. It may grow weakly, and its leaves may look pale and thin.

lighttop of leafundersidetiny holesair goes in
A leaf: light falls on the top, and air goes in through tiny holes, mostly on the underside.

Key ideas

  • Leaves use light, water and carbon dioxide from the air to make food.
  • Carbon dioxide is a gas in the air.
  • Leaves take in air through tiny holes, mostly on the underside.
  • A plant in the dark cannot make food from light, so it grows weakly.
Worked example 3.2.1
Which gas do leaves take in from the air to make food? Write the gas.

Method. Think about the gas that leaves take in through their holes.

  1. Read the question. The question asks for the gas that leaves take in from the air.
    gas from the air
  2. Think about the holes. Leaves take in a gas through their tiny holes.
    tiny holes
  3. Name the gas. The gas that leaves take in from the air is carbon dioxide.
    carbon dioxide
  4. Write the answer.
    carbon dioxide

Check. Plants take in carbon dioxide and use it to make food. ✓

Worked example 3.2.2
Two bean plants are kept for three weeks. Plant A is on a sunny windowsill, and plant B is in a dark cupboard. Which plant is more likely to be pale and thin? Write A or B.

Method. Think about which plant can use light to make food.

  1. Read A. Plant A is on a sunny windowsill, so it gets light.
    A: light
  2. Read B. Plant B is in a dark cupboard, so it cannot make food from light.
    B: no light
  3. Choose the plant. The plant that cannot make food from light is more likely to be pale and thin.
    B
  4. Write the answer.
    B

Check. A plant in the dark grows weakly. ✓

Watch out. The plant in the light is not the pale one, because it can make food.

Worked example 3.2.3
Sarah says plants do not need air, because they only need light and water. Is Sarah right? Write yes or no.

Method. Check the list of needs.

  1. Read the claim. Sarah says plants only need light and water.
    light and water only
  2. Check the list. Plants also need air, which leaves use to make food.
    air is needed
  3. Decide. So Sarah is not right.
    no
  4. Write the answer.
    no

Check. Air is one of the five needs of a plant. ✓

Watch out

Watch out: leaves do not take in carbon dioxide through their roots. They take it in through tiny holes, mostly on the underside. The roots take in water and nutrients from the soil.

Try it at home or school (with a grown-up). With a grown-up, look at a leaf from a houseplant or a tree, using a magnifying glass. Gently look at the underside. Can you see any tiny holes? Some leaves show them more clearly than others. Draw the leaf and label the top and the underside. Do not pick the leaf. Wash your hands afterwards.

Exam tip

Grown-up tip. Ask: “Which side of the leaf gets the light? Which side might the air go in through?” Let your child show you where the tiny holes are, if they can see them.

Exercise 3B  Light and air: making food in the leaves

1
FLeaves take in a gas called carbon ___. Write the missing word.
2
FLeaves use light to make ___. Write the missing word.
3
FWhich gas do plants give out that people breathe in? Write the gas.
4
FLook at the leaf picture. Are most of the tiny holes on the top or the underside of the leaf? Write top or underside.
lighttop of leafundersidetiny holesair goes in
5
FFill in the gaps.
(a)Leaves use light, water and carbon dioxide to make ___.
(b)Plants in the dark grow ___.
6
FWhich bean plant is more likely to be healthy: the one on the sunny windowsill, or the one in the dark cupboard? Write the one.
7
PSMia counts 9 green leaves on a plant on the windowsill, and 3 pale leaves on a plant in a cupboard. How many more leaves does the windowsill plant have?
8
PSRuby says a plant in the dark will make as much food as a plant in the light. Is Ruby right? Write yes or no.
9
PSWorking scientifically. Plan a test to find out whether light helps a leaf to make food. Write one thing that you must keep the same for both plants.
10
RIs this true or false? Leaves take in oxygen from the air to make food. Write true or false.
11
RExplain in one sentence why a plant on a windowsill grows better than one in a cupboard.
3.3

Water and nutrients from the soil

Year 3
Explore the requirements of plants for life and growth: water and nutrients from the soil, taken in by the roots
Video lesson: Water and nutrients from the soilComing soon
Story. Amira’s bean plant has pale leaves. Its pot has old soil that has been used for many years. Her teacher says, “Plants take nutrients from the soil. After a long time, the soil may not have enough left.”

The roots take in water from the soil. The water carries nutrients into the roots with it. Nutrients help the plant to grow well. Two examples of nutrients are nitrogen and phosphorus.

Nutrients are not food. A plant makes its food in its leaves, using light, water and carbon dioxide. The nutrients from the soil help the plant to build the parts it needs to grow.

Roots also need some air in the soil. The spaces between the soil crumbs hold air. Soil that is always soggy has little air in it, and this can harm the roots.

waternutrients (minerals)small stonesold plant bits
Soil holds water, nutrients, small stones and bits of old plants. The roots take in water and nutrients.

Key ideas

  • Roots take in water and nutrients from the soil.
  • Nutrients are substances in the soil that a plant needs to grow well.
  • Nutrients are not food. Leaves make food from light, water and carbon dioxide.
  • Soggy soil with very little air can harm the roots.
Worked example 3.3.1
Where do the roots take nutrients from? Write the place.

Method. Think about where the roots are.

  1. Think about the roots. The roots are in the soil, and they take in water and nutrients.
    roots in soil
  2. Think about the nutrients. The nutrients come from the soil, and the roots take them in.
    from the soil
  3. Name the place. The roots take nutrients from the soil.
    soil
  4. Write the answer.
    soil

Check. The soil holds the nutrients that the roots take in. ✓

Worked example 3.3.2
Amira’s plant has pale leaves in old soil. Which need might be short? Write the need.

Method. Think about what the old soil may have less of.

  1. Read the story. The soil is old, and it has been used for a long time.
    old soil
  2. Think about the soil. Plants use up the nutrients in the soil over time.
    nutrients used up
  3. Name the need. The need that may be short is nutrients from the soil.
    nutrients from soil
  4. Write the answer.
    nutrients from soil

Check. Pale leaves can show that a plant is short of nutrients. ✓

Watch out. The leaves are not short of light here. The soil is the place where the need is short.

Worked example 3.3.3
Maya says nutrients are the food that a plant eats. Is she right? Write no, and say what the leaves make food from.

Method. Check what nutrients are and what food is.

  1. Read the claim. Maya says nutrients are a plant’s food.
    claim
  2. Check the facts. Nutrients are substances the plant takes in from the soil to grow well. They are not food.
    not food
  3. Name what the leaves use. Leaves make food from light, water and carbon dioxide.
    light, water, carbon dioxide
  4. Write the answer.
    No. Accept any answer that says the leaves make food from light, water and carbon dioxide, and nutrients are not food.

Check. A plant makes its own food in its leaves. ✓

Watch out

Watch out: do not say that roots take in light. Roots take in water and nutrients from the soil. Light is used by the leaves.

Try it at home or school (with a grown-up). Put a spoonful of garden soil onto a plate or tray, with a grown-up. Look at it with a magnifying glass. Can you find small stones, dark bits of old leaves, and crumbs of soil? Do not eat or taste the soil. Wash your hands well afterwards.

Exam tip

Grown-up tip. Ask: “What is in the soil? What do the roots take out of it?” Let your child point to a stone and to a bit of old leaf, and say which of these could be a nutrient.

Exercise 3C  Water and nutrients from the soil

1
FWhich two things do the roots take in from the soil? Write two.
2
FFill in the gap: nutrients come from the ___. Write the missing word.
3
FAre nutrients food for a plant? Write yes or no.
4
FLook at the soil picture. What colour are the drops that show water? Write the colour.
waternutrients (minerals)small stonesold plant bits
5
FLook at the soil picture. What colour are the nutrient dots? Write the colour.
waternutrients (minerals)small stonesold plant bits
6
FFill in the gaps.
(a)Roots take in ___ and nutrients from the soil.
(b)Soggy soil with no ___ can harm the roots.
7
PSBen’s bean plant lives in a pot of old soil that has been used for many years. He waters it every day, and it gets plenty of light. Its leaves go pale. Which need is probably short? Write the need.
8
PSA pot of soil is given 500 ml of water. 120 ml of the water drains away. How many millilitres of water stay in the soil?
9
PSWorking scientifically. Plan a fair test to see whether nutrients help a bean plant to grow. Write one thing that you would keep the same in both pots.
10
RTom says roots take in light from the soil. Is Tom right? Write no, and say which part of the plant uses light.
11
RExplain in one sentence why soggy soil can harm roots.
3.4

Room to grow, and how plants differ

Year 3
Explore the requirements of plants for life and growth: room to grow, and how the needs of plants vary from plant to plant
Video lesson: Room to grow, and how plants differComing soon
Story. At the school garden, Zainab finds a cactus in a pot, a water lily in a pond and a sunflower by the fence. Oliver says, “They look so different. Do they all need the same things?”

Room to grow means space for the roots to spread out in the soil, and space for the leaves to spread out in the light. When plants are crowded, they must share the light, the water and the nutrients. A crowded plant may grow less well.

Plants do not all need the same amount of each thing. They vary from plant to plant:

cactuslittle waterwater lilylives in watersunflowerlots of light
Three different plants: a cactus that needs little water, a water lily in a pond, and a sunflower that needs lots of light.
1 plant3 plants, crowded
One plant in a pot has room to grow. Three plants crowded into one pot have to share.

Key ideas

  • Room to grow means space for the roots and the leaves.
  • Crowded plants share the light, water and nutrients.
  • A cactus needs little water. A water lily lives in water. A sunflower needs lots of light.
  • Plants do not all need exactly the same things.
Worked example 3.4.1
Which plant in the picture needs the least water? Write its name.
cactuslittle waterwater lilylives in watersunflowerlots of light

Method. Read the description under each plant.

  1. Read the cactus. The cactus needs little water.
    little water
  2. Read the water lily. The water lily lives in water, so it needs a lot of water.
    lives in water
  3. Choose the plant. So the cactus is the plant that needs the least water.
    cactus
  4. Write the answer.
    cactus

Check. A cactus lives where there is very little rain. ✓

Worked example 3.4.2
This table shows the average height of bean plants after 3 weeks. Which pot gave the tallest plants?
PotAverage height (cm)
1 plant in the pot24
2 plants in the pot19
3 plants in the pot13

Method. Find the biggest number in the height column.

  1. Read the heights. The heights are 24 cm, 19 cm and 13 cm.
    24, 19, 13
  2. Find the biggest. The biggest height is 24 cm, which is in the pot with 1 plant.
    24 cm is biggest
  3. Name the pot. So the pot with one plant gave the tallest plants.
    1 plant
  4. Write the answer.
    1 plant in the pot

Check. The plants with room to grow were the tallest. ✓

Worked example 3.4.3
Tom says that all plants need exactly the same amount of water. Is Tom right? Write yes or no.

Method. Think about the three plants you have read about.

  1. Read the plants. The cactus needs little water, and the water lily lives in water.
    different amounts
  2. Decide. Plants need different amounts of water, so Tom is not right.
    not right
  3. Write the answer.
    no

Check. Plants vary from plant to plant. ✓

Watch out

Watch out: a plant that needs little water is not the same as a plant that needs no water. Every plant needs some water, but the amount differs from plant to plant.

Try it at home or school (with a grown-up). With a grown-up, visit a park, a garden or the school grounds. Find two different plants that look very different. Write down what each one looks like, and where it grows. Do not pick or pull any plant. Wash your hands afterwards.

Exam tip

Grown-up tip. Ask: “Where does this plant grow best? Does it need a lot of sun or a lot of water?” Let your child compare two plants and say how they are different.

Exercise 3D  Room to grow, and how plants differ

1
FWhat does room to grow mean? Write one short sentence.
2
FWhich plant lives in a pond? Write its name.
3
FWhich plant stores water in a thick stem? Write its name.
4
FWhich plant needs lots of light? Write its name.
cactuslittle waterwater lilylives in watersunflowerlots of light
5
FFill in the gaps.
(a)Crowded plants must ___ the light and water.
(b)A cactus needs little ___.
6
FLook at the picture of the two pots. Which pot has room to grow: the pot with 1 plant, or the pot with 3 plants? Write 1 or 3.
1 plant3 plants, crowded
7
PSA class sets up two pots for a sunflower test. Pot A has 1 sunflower and pot B has 2 sunflowers. Which pot gives each sunflower more room? Write pot A or pot B.
8
PSThis table shows the average height of bean plants after 3 weeks. How much taller is the plant in the pot with 1 plant than the plant in the pot with 3 plants?
PotAverage height (cm)
1 plant in the pot24
2 plants in the pot19
3 plants in the pot13
9
PSWorking scientifically. Predict which will be taller after 3 weeks: a bean plant with room to grow, or a bean plant crowded with 3 others in one pot. Write which one.
10
RSam says a sunflower and a cactus need exactly the same things. Is Sam right? Write no, and give one difference.
11
RExplain in one sentence why crowded plants may grow less well than plants with room to grow.
3.5

How water travels up the plant

Year 3
Investigate the way in which water is transported within plants: from the roots, up the stem, to the leaves
Video lesson: How water travels up the plantComing soon
Story. Kofi puts a celery stick in a glass of water with blue food colouring. Priya asks, “How will the blue get up to the leaves?” Kofi says, “Maybe the water climbs up through the middle of the stick.”

The roots take in water from the soil. The water then travels up through the stem to the leaves and flowers. It moves through tiny tubes inside the roots, the stem and the leaves. The scientific name for these tubes is xylem.

Moving something from one place to another is called transport. So this is called water transport: the water is carried up the plant to the places where it is needed.

Some water leaves the plant through tiny holes in the leaves, as water vapour. This loss of water helps to pull more water up the stem from the roots.

water vapourwater moves uptiny tubesroots
Water goes up from the roots, through tiny tubes in the stem, to the leaves. Some water leaves the leaves as vapour.

Key ideas

  • Water travels up the plant through tiny tubes, called xylem.
  • Water starts in the roots and travels up the stem to the leaves.
  • Water leaves the leaves as water vapour.
  • Transport means moving something from one place to another.
Worked example 3.5.1
Kofi measures the coloured line on the celery stick. Use the table. How far up the stick has the coloured water moved after 1 hour?
TimeHeight of coloured line
after 1 hour3 cm
after 3 hours9 cm
after 5 hours17 cm

Method. Find the row for 1 hour, and read the height.

  1. Find the row. The first row is for after 1 hour.
    first row
  2. Read the height. The coloured line is at 3 cm after 1 hour.
    3 cm
  3. Check the start. The coloured water started at the bottom of the stick, at 0 cm.
    started at 0
  4. Write the answer.
    3 cm

Check. The coloured line rose 3 cm from 0 cm. ✓

Worked example 3.5.2
Use the same table. How far did the coloured water rise between 3 hours and 5 hours?

Method. Take the height at 3 hours away from the height at 5 hours.

  1. Read the two heights. The line was at 9 cm after 3 hours and at 17 cm after 5 hours.
    9 and 17
  2. Find the rise. The rise is the bigger height minus the smaller height.
    17 − 9 = 8
  3. Write the answer.
    8 cm

Check. 9 + 8 = 17, so the answer is right. ✓

Worked example 3.5.3
Put these in the order that water travels from the soil: leaves, soil, stem, roots. Write the order.

Method. Start in the soil, and follow the water to the leaves.

  1. Start in the soil. The water starts in the soil.
    soil first
  2. Go to the roots. The roots take in the water from the soil.
    roots next
  3. Go up the stem. The water travels up the stem, and reaches the leaves last.
    stem then leaves
  4. Write the answer.
    soil, roots, stem, leaves

Check. Soil, roots, stem, leaves: the water reaches the leaves last. ✓

Watch out

Watch out: the water does not travel down the stem to the roots. It goes up. The roots take the water in, and the stem carries it up to the leaves.

Try it at home or school (with a grown-up). With a grown-up, put a celery stick in a clear glass of water with a few drops of food colouring. Leave it for an hour or two, and then look at the stick. Ask your grown-up to cut the stick across, and look at the coloured dots or lines. Do not drink the coloured water. Wash your hands afterwards.

Exam tip

Grown-up tip. Ask: “Where did the blue colour start? Where has it got to now? Why did it go up the stick?” Let your child point with a finger from the glass, up the stick, to the leaves.

Exercise 3E  How water travels up the plant

1
FWater moves up the plant through tiny ___ in the stem. Write the missing word.
2
FWhat is the scientific name for the tubes that carry water up a plant? Write the name.
3
FWhat is the word for moving something from one place to another? Write the word.
4
FWater leaves a plant through tiny holes in its ___. Write the missing word.
5
FLook at the transport picture. Does the water move up the stem or down the stem? Write up or down.
water vapourwater moves uptiny tubesroots
6
FFill in the gaps.
(a)Water starts in the ___ and travels up the stem.
(b)Water is carried up to the ___ of the plant.
7
PSUse the celery table. Between which two times did the coloured water rise the most?
TimeHeight of coloured line
after 1 hour3 cm
after 3 hours9 cm
after 5 hours17 cm
8
PSMo says the coloured water rose 17 cm in the first 5 hours. Is Mo right? Write yes or no.
9
PSWorking scientifically. Predict: if a celery stick is put in red water instead of blue water, will the red colour reach the leaves? Write yes or no, and give a reason.
10
RExplain in one sentence why a cut stem would stop water reaching the leaves.
11
RKofi says the water in a plant only goes up, and never leaves the plant. Is Kofi right? Write no, and say how water leaves a plant.
3.6

Fair tests with plants

Year 3
Investigate what plants need with a fair test: change one thing, keep the rest the same, measure, record and draw a conclusion
Video lesson: Fair tests with plantsComing soon
Story. Class 3C wants to find out whether light helps a bean plant to grow. Noah says, “Put one plant on the windowsill, and one in the dark cupboard. Measure both of them every week.” Priya says, “They must be the same in every other way.”

A fair test changes only one thing. Everything else is kept the same. To test whether light helps a bean plant to grow, the class:

The class measures both plants with a ruler at the start and after 3 weeks. They write the results in a table, and show the growth on a bar chart. Then they write a conclusion, which says what the results show.

A: window (light)B: dark cupboard
A fair test: two identical bean plants, and the only thing that changes is where each plant is kept.
0510152025cm15 cmwindow3 cmcupboard
How much each bean plant grew in 3 weeks: the window plant grew 15 cm, and the cupboard plant grew 3 cm.

Key ideas

  • A fair test changes only one thing and keeps the rest the same.
  • Measure the plants at the start and at the end, using a ruler.
  • A bar chart can show how much each plant grew.
  • A conclusion says what the results show.
Worked example 3.6.1
In the light test, what is the only thing that changes? Write one word.

Method. Look for the one thing that is different between the two plants.

  1. Compare the two plants. Both plants have the same pot, soil and water, but one is in the light and one is in the dark.
    light differs
  2. Name the one thing. The one thing that changes is the amount of light.
    light
  3. Write the answer.
    light

Check. Only the light changes in a fair test. ✓

Worked example 3.6.2
The window plant grew from 6 cm to 21 cm. How many cm did it grow?

Method. Take the height at the start away from the height at the end.

  1. Read the two heights. The plant was 6 cm at the start and 21 cm at the end.
    6 and 21
  2. Find the growth. The growth is the end height minus the start height.
    21 − 6 = 15
  3. Write the answer.
    15 cm

Check. 6 + 15 = 21, so the answer is right. ✓

Worked example 3.6.3
The cupboard plant grew 3 cm. How much more did the window plant grow than the cupboard plant?

Method. Take the smaller growth away from the bigger growth.

  1. Read the two growths. The window plant grew 15 cm and the cupboard plant grew 3 cm.
    15 and 3
  2. Find the difference. The difference is how much more the window plant grew.
    15 − 3 = 12
  3. Write the answer.
    12 cm

Check. 3 + 12 = 15, so the answer is right. ✓

Watch out

Watch out: one test is not enough. A class repeats the test with more than one plant in each place, so that one unusual plant does not mislead them.

Try it at home or school (with a grown-up). With a grown-up, set up two identical small pots of bean or cress seeds: one by a sunny window and one in a dark cupboard. Use the same soil and the same amount of water for both. Measure the height of each plant with a ruler every few days, and write the results in a table. Do not put anything in the cupboard that could harm the plant. Wash your hands afterwards.

Exam tip

Grown-up tip. Ask: “What is the one thing that changes? What must stay the same?” Help your child to measure each plant from the soil to the top, in cm, and to write the results in a table with a heading for each column.

Exercise 3F  Fair tests with plants

1
FIn a fair test, how many things change? Write the number.
2
FWhich must be the same for both plants? Write A, B or C. A: the place where the plant is kept. B: the amount of water. C: the amount of light.
3
FFill in the gaps.
(a)A fair test changes only ___ thing.
(b)A bar chart can show how much each plant ___.
4
FAt the start and at the end of the test, what do you measure for each bean plant? Write one word.
5
FWhich tool is best for measuring the height of each bean plant? Write the tool.
6
FLook at the bar chart. Which plant grew more: the window plant or the cupboard plant? Write the word window or cupboard.
0510152025cm15 cmwindow3 cmcupboard
7
FLook at the bar chart. How many cm did the window plant grow?
0510152025cm15 cmwindow3 cmcupboard
8
PSMo sets up 3 pots in the light and 4 pots in the dark. How many pots are there in all?
9
PSRuby says the cupboard plant grew less because it was not watered. Is this a fair conclusion from this test? Write yes or no.
10
PSWorking scientifically. Predict which plant will be taller after 3 more weeks, the window plant or the cupboard plant. Write one reason for your prediction.
11
RExplain why the test should be repeated with more than one bean plant in each place.

Chapter summary

SkillMethod
Five needsAir, light, water, nutrients from the soil and room to grow. Plants need all five to grow and stay healthy.
Air and lightLeaves use light, water and carbon dioxide from the air to make food. Carbon dioxide enters through tiny holes.
Water and nutrientsRoots take in water and nutrients from the soil. Nutrients help a plant to grow well, but they are not food.
Room to growPlants need space for their roots and leaves. Crowded plants share the light, water and nutrients.
Plants differA cactus needs little water, a water lily lives in water, and a sunflower needs lots of light.
Water transportWater travels from the roots, up the stem, through tiny tubes (xylem), to the leaves. Some water leaves the leaves as vapour.
Fair testsChange one thing, keep the rest the same, measure, show the results in a table or bar chart, and write a conclusion.

Can you…?

  • I can name the five things a plant needs: air, light, water, nutrients from the soil and room to grow
  • I can say what leaves use light and carbon dioxide for, and why a plant in the dark grows weakly
  • I can say what roots take in from the soil, and explain why nutrients are not food
  • I can explain why crowded plants may grow less well, and how plants differ in what they need
  • I can describe how water travels up the stem through tiny tubes, from the roots to the leaves
  • I can plan a fair test with a plant, and read a table and a bar chart of the results

Key terms

need
something a living thing must have to live and grow
nutrient
a substance in the soil that a plant takes in through its roots to help it grow well; nutrients are not food
carbon dioxide
a gas in the air that leaves take in and use, with light and water, to make food
room to grow
space for the roots and leaves of a plant to spread out
vary
to be different, from one plant to another
transport
moving something from one place to another
water transport
the movement of water through a plant, from the roots, up the stem, to the leaves
xylem
the tiny tubes that carry water up through the roots, stem and leaves of a plant
water vapour
water in the form of a gas, which can leave a plant through its leaves
fair test
a test that changes only one thing and keeps everything else the same
conclusion
what the results of a test show
bar chart
a chart that uses bars of different heights to show amounts

Exercise 3Z  Check-up

1
Write one thing that a plant needs from the soil.
2
Which gas do leaves take in from the air to make food? Write the gas.
3
Which part of the plant takes in nutrients from the soil? Write the part.
4
Use the celery table. How far did the coloured water rise between 1 hour and 3 hours?
TimeHeight of coloured line
after 1 hour3 cm
after 3 hours9 cm
after 5 hours17 cm
5
Two pots are set up. Pot A has 1 bean plant and pot B has 3 bean plants. Which pot gives each plant more room? Write A or B.
6
Which plant needs little water, because it stores water in a thick stem? Write the name.
7
Tom says plants make food from nutrients in the soil. Is Tom right? Write no, and say where plants make their food.
8
Which tubes carry water up the stem of a plant? Write the scientific name.
9
Working scientifically. In a fair test on light, one bean plant is on a windowsill and another is in a dark cupboard. Write one thing that must stay the same for both plants.
10
Explain in one sentence why soggy soil can harm the roots of a plant.

Total 20 marks. Allow about 20 minutes.

Exercise 3X  Practice test questions

1
FWhich gas do leaves take in from the air? Write the gas.[1 mark]
2
FName one nutrient that a plant takes in from the soil. Write one nutrient.[1 mark]
3
FLook at the soil picture. What colour are the drops that show water? Write the colour.
waternutrients (minerals)small stonesold plant bits
[1 mark]
4
RExplain in one sentence why a plant in a dark cupboard may grow weakly.[2 marks]
5
RExplain why three plants crowded into one pot may grow less well than one plant in a pot. Write one or two sentences.[2 marks]
6
FLook at the transport picture. Write up or down: which way does water move up the stem?
water vapourwater moves uptiny tubesroots
[1 mark]
7
PSUse the celery table. How far did the coloured water rise between 1 hour and 5 hours? Write the distance, and the part of the plant that the water travelled through.
TimeHeight of coloured line
after 1 hour3 cm
after 3 hours9 cm
after 5 hours17 cm
[3 marks]
8
PSA class wants to test whether light helps a bean plant to grow. Write two things that must stay the same, and name the one thing that changes.[3 marks]
9
FName the five things a plant needs from its surroundings. Then give one reason why light is needed.[3 marks]
10
RMo says that a plant does not need nutrients because it makes its own food. Is Mo right? Write no, and explain what nutrients are for. Write one or two sentences.[3 marks]
← Chapter 2: Parts of a flowering plantChapter 4: The life cycle of a flowering plant →

Websink Prep UK is an independent site. It is not affiliated with, endorsed by or sponsored by AQA, Pearson Edexcel, OCR, WJEC, Eduqas, CCEA, SQA, GL Assessment, CEM or the Department for Education. All exam board names and trademarks belong to their owners. Past papers are linked from the exam boards' own websites and are not hosted here.

About Websink Prep UK · Find a tutor · Privacy · Terms · Cookie settings