CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.1A
Microorganisms vocabulary
Use these words to complete the sentences below.
You can use each word once, more than once or not at all.

algae bacteria bacterium cell colony dead

fungi fungus microorganism protozoa sterile yeast

1 An organism that is so small we can only see it with a microscope is called a _______________.

2 Mushrooms and toadstools are examples of _______________.

3 _______________ are single-celled microorganisms that have cells much smaller than animal cells or
plant cells.

4 One example of a single-celled fungus is _______________.

5 A group of microorganisms growing on agar jelly is called a _______________.

6 When all the living organisms on something have been killed, we say that it is _______________.

7 _______________ are single-celled microorganisms with cells like animal cells.

8 Single-celled microorganisms with cells like plant cells are called _______________.

9 The plural of fungus is _______________.

10 The singular of bacteria is _______________.

Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman and Michael Smyth © Cambridge University Press 2021 1
 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.1B
Microorganisms vocabulary
Complete the sentences below.

1 An organism that is so small we can only see it with a microscope is called a m_______________.

2 Mushrooms and toadstools are examples of f_______________.

3 B_______________ are single-celled microorganisms that have cells much smaller than animal cells
or plant cells.

4 One example of a single-celled fungus is y_______________.

5 A group of microorganisms growing on agar jelly is called a c_______________.

6 When all the living organisms on something have been killed, we say that it is s_______________.

7 P_______________ are single-celled microorganisms with cells like animal cells.

8 Single-celled microorganisms with cells like plant cells are called a_______________.

9 The plural of fungus is f_______________.

10 The singular of bacteria is b_______________.

Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman and Michael Smyth © Cambridge University Press 2021 2
 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.1C
Microorganisms vocabulary
Complete the sentences below.

1 An organism that is so small we can only see it with a microscope is called a _______________.

2 Mushrooms and toadstools are examples of _______________.

3 _______________ are single-celled microorganisms that have cells much smaller than animal cells or
plant cells.

4 One example of a single-celled fungus is _______________.

5 A group of microorganisms growing on agar jelly is called a _______________.

6 When all the living organisms on something have been killed, we say that it is _______________.

7 _______________ are single-celled microorganisms with cells like animal cells.

8 Single-celled microorganisms with cells like plant cells are called _______________.

9 The plural of fungus is _______________.

10 The singular of bacteria is _______________.

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.2A
Food web in a pond
There is a small pond in Arun’s garden.
Algae and water plants grow in the pond. Tadpoles and snails feed on the algae and water plants.
Dragonfly larvae and newts eat tadpoles. Herons eat snails.

1 Complete the food web for Arun’s pond.

2 How many producers are there in your food web?

__________________________________________________________________________________

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

3 How many consumers are there in your food web?

__________________________________________________________________________________
4 Complete the sentence about the arrows in your food web. Circle the correct word.

energy
The arrows show how food flows through the food web.
animals

Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman and Michael Smyth © Cambridge University Press 2021 5
 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.2B
Food web in a pond
There is a small pond in Arun’s garden.
Algae and water plants grow in the pond. Tadpoles and snails feed on the algae and water plants.
Dragonfly larvae and newts eat tadpoles. Herons eat snails.

1 Draw the food web for Arun’s pond.

Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman and Michael Smyth © Cambridge University Press 2021 6
 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

2 How many producers are there in your food web?

__________________________________________________________________________________
3 How many consumers are there in your food web?

__________________________________________________________________________________
4 Complete the sentence about the arrows in your food web. Circle the correct word.

energy
The arrows show how food flows through the food web.
animals

Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman and Michael Smyth © Cambridge University Press 2021 7
 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.2C
Food web in a pond
There is a small pond in Arun’s garden.
Algae and water plants grow in the pond. They are eaten by tadpoles. Dragonfly larvae and newts are
predators of these herbivores.
Snails also eat algae and water plants. They are prey of herons that visit the pond.

1 Draw the food web for Arun’s pond.

Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman and Michael Smyth © Cambridge University Press 2021 8
 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

2 How many producers are there in your food web?

__________________________________________________________________________________
3 How many consumers are there in your food web?

__________________________________________________________________________________
4 Explain what the arrows in your food web represent.

__________________________________________________________________________________

__________________________________________________________________________________

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.3A
Bacteria in milk
Some bacteria are decomposers. They make organic matter decay. They can make food go bad.
Bacteria can make milk go sour. Zara did an experiment to find out if heating milk could stop bacteria
growing in it.
Zara:
• collects two bottles with lids
• fills each bottle with fresh milk
• leaves one bottle, A, on the bench
• heats the other bottle, B, to 63°C for 30 minutes
• puts both bottles into a test-tube rack on the bench.

Zara adds two drops of blue dye to each bottle.

She knows that the dye goes pink and then white if there are a lot of living bacteria in the milk.

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

1 Zara wants to find out if heating the milk stops bacteria from growing in it. Why does she not heat
one of the bottles of milk?

__________________________________________________________________________________
2 The blue dye changes to pink and then white in bottle A.
Tick the correct explanation for this.
All the bacteria in bottle A were dead.

The dye in bottle A was destroyed when it was heated.

Zara added too much dye to bottle A.

There were lots of living bacteria in bottle A.

3 Zara thinks that heating the milk to 63 °C for 30 minutes kills nearly all the bacteria in the milk.
Predict what happens to the colour of the dye if she is correct.

__________________________________________________________________________________

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.3B
Bacteria in milk
Some bacteria are decomposers. They make organic matter decay. They can make food go bad.
Bacteria can make milk go sour. Zara did an experiment to find out if heating milk could stop bacteria
growing in it.
Zara:
• collects two bottle with lids
• fills each bottle with fresh milk
• leaves one bottle, A, on the bench
• heats the other bottle, B, to 63°C for 30 minutes
• puts both bottles into a test-tube rack on the bench.

Zara adds two drops of blue dye to each bottle.

She knows that the dye goes pink and then white if there are a lot of living bacteria in the milk.

Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman and Michael Smyth © Cambridge University Press 2021 12
 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

1 Heating milk to 63 °C for 30 minutes is called pasteurisation.

Zara wants to find out if pasteurising the milk stops bacteria from growing in it.
Why does she not heat one of the bottles of milk?

__________________________________________________________________________________
2 The blue dye changes to pink and then white in bottle A.
Tick the correct explanation for this.
All the bacteria in bottle A were dead.

The dye in bottle A was destroyed when it was heated.

Zara added too much dye to bottle A.

There were lots of living bacteria in bottle A.

3 Zara thinks that heating the milk to 63°C for 30 minutes kills nearly all the bacteria in the milk.
Predict what happens to the colour of the dye if she is correct.

__________________________________________________________________________________
4 Zara leaves both of her bottles of milk to the next day.
Then she tests the pH in each bottle.
Here are her results.
Bottle A pH 5
Bottle B pH 6
a Which bottle contains the most acid?

_______________________________________________________________________________
b Suggest why this bottle contains more acid than the other bottle.

_______________________________________________________________________________

_______________________________________________________________________________

_______________________________________________________________________________

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

5 Another way of stopping milk from going sour is to heat it to a very high temperature.
The milk is then sealed in an air-tight container.
This is called ultra heat treatment, or UHT.
Explain why UHT milk stays fresh for longer than pasteurised milk.

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.3C
Bacteria in milk
Some bacteria are decomposers. They make organic matter decay. They can make food go bad.
Bacteria can make milk go sour, because they change some of its contents to acid. Anna did an
experiment to find out if heating milk could stop bacteria growing in it.
Zara:
• collects two bottle with lids
• fills each bottle with fresh milk
• leaves one bottle, A, on the bench
• heats the other bottle, B, to 63°C for 30 minutes
• puts both bottles into a test-tube rack on the bench.

Zara adds two drops of blue dye to each bottle.

She knows that the dye goes pink and then white if there are a lot of living bacteria in the milk.

Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman and Michael Smyth © Cambridge University Press 2021 15
 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

1 Heating milk to 63°C for 30 minutes is called pasteurisation.

Zara wants to find out if pasteurising the milk stops bacteria from growing in it.
Why does she not heat one of the bottles of milk?

__________________________________________________________________________________
2 The table shows Zara’s results.

Time in minutes Colour of milk in bottle A Colour of milk in bottle B

0 blue blue

5 blue blue

10 pink blue

15 pink blue

20 white blue

Suggest an explanation for these results.

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

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3 Zara leaves both of her bottles of milk to the next day.

Then she tests the pH in each bottle.
Here are her results.
Bottle A pH 5
Bottle B pH 6
Suggest an explanation for these results.

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________
4 Another way of stopping milk from going sour is to heat it to a very high temperature.
The milk is then sealed in an air-tight container.
This is called ultra heat treatment, or UHT.
Explain why UHT milk stays fresh for longer than pasteurised milk.

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman and Michael Smyth © Cambridge University Press 2021 17
 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.4A
Decomposers and plant growth
Some scientists did an experiment to test this hypothesis:

Plants grow better in soil with decomposers than in soil without decomposers.

They did their experiment in a glasshouse. They divided the glasshouse into equal-sized plots, A and B.
In plot A, they put soil containing a lot of microorganisms that act as decomposers.
In plot B, they put soil that had been heated to kill all the microorganisms.
They sowed grass seeds on both soils. They allowed the grass to grow for several years.
1 Which variable do the scientists change? Tick the correct answer.
Whether or not the soil contains decomposers.

How much light the grass gets.

Whether the plants are in a glasshouse or outside.

The mass of the grass plants.

The volume of water given to the grass plants.

2 Which variables should the scientists keep the same?
Tick the three correct answers.
How many decomposers there are in the soil.

How much light the grass gets.

Whether the plants are in a glasshouse or outside.

The mass of the grass plants.

The volume of water given to the grass plants.

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

3 The scientists found that the mass of grass in plot A was more than the mass of grass in plot B.
What conclusion can they make?
Tick the correct answer.
Grass grows better in a glasshouse than in a field.

Grass grows more when there are decomposers in the soil.

Grass needs light and carbon dioxide to grow well.

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.4B
Decomposers and plant growth
Some scientists did an experiment to test this hypothesis:

Plants grow better in soil with decomposers than in soil without decomposers.

They did their experiment in a glasshouse. They divided the glasshouse into plot A and plot B.
In plot A, they put soil containing a lot of microorganisms that act as decomposers.
In plot B, they put soil that had been heated to kill all the microorganisms.
They sowed grass seeds on both soils. They allowed the grass to grow for several years.
Every six months, they collected the grass leaves from a small and equal area of each plot. They
measured the mass of the grass leaves.
1 Which variable do the scientists change? Tick the correct answer.
Whether or not the soil contains decomposers.

How much light the grass gets.

Whether the plants are in a glasshouse or outside.

The mass of the grass plants.

The volume of water given to the grass plants.

2 Which variables should the scientists keep the same? Tick the three correct answers.
How many decomposers there are in the soil.

How much light the grass gets.

Whether the plants are in a glasshouse or outside.

The mass of the grass plants.

The volume of water given to the grass plants.

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Here are the results of the experiment.

Time in months Mass of grass in sample Mass of grass in sample from

from plot A in g plot B in g

0 0 0

6 80 70

12 220 160

18 250 170

24 240 150

30 250 130

3 The results for plot A are plotted on the grid. Plot the results for plot B.

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4 Do the results support the scientists’ hypothesis? _______________

Explain your answer.

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________
5 Suggest two ways in which the scientists could improve their experiment to make their results more
reliable.

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

Name ___________________________________ Date _____________

Worksheet: 7.4C
Decomposers and plant growth
Some scientists did an experiment to test this hypothesis:

Plants grow better in soil with decomposers than in soil without decomposers.

They did their experiment in a glasshouse. They divided the glasshouse into plot A and plot B.
In plot A, they put soil containing a lot of microorganisms that act as decomposers.
In plot B, they put soil that had been heated to kill all the microorganisms.
They sowed grass seeds on both soils. They allowed the grass to grow for several years.
Every six months, they collected the grass leaves from a small and equal area of each plot. They
measured the mass of the grass leaves.
1 Which variable do the scientists change?

__________________________________________________________________________________
2 Suggest three variables that the scientists should keep the same.

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

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 CAMBRIDGE LOWER SECONDARY SCIENCE 7: UNIT 7: MICROORGANISMS IN THE ENVIRONMENT

3 Here are the results of the experiment.

Time in months Mass of grass in sample Mass of grass in sample from

from plot A in g plot B in g

0 0 0

6 80 70

12 220 160

18 250 170

24 240 150

30 250 130

Show the information given in the table by marking a point for each result onto the grid. Draw two
line graphs, one for plot A and one for plot B.

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4 Do the results support the scientists’ hypothesis? _______________

Explain your answer.

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________
5 Suggest an explanation for these results.

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________
6 Suggest two ways in which the scientists could improve their experiment to make their results more
reliable. Explain each of your suggestions.

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

__________________________________________________________________________________

Cambridge Lower Secondary Science 7 – Mary Jones, Diane Fellowes-Freeman and Michael Smyth © Cambridge University Press 2021 26