CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B1.

Name Date

B1.1: Specialised cell circus

Cells have a remarkable variety of sizes and shapes. In this activity, you will work in pairs and move around your classroom to complete a research
task organised by your teacher.
Task 1 In your pair, decide on a one-sentence definition of the term specialised. Once you have done this, let your teacher know so that they can
check your sentence.

Task 2 Move around the six stations that your teacher has organised around the room. At each station:
• Draw a diagram of the cell. Remember that your diagram should be drawn with a sharp pencil and no shading.
• Summarise the function of the cell by using the key words listed in Chapter B1.
• List the structures that are found in this cell that adapt it to this function.
Record your work in the table on pages 3, 4 and 5.

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• Task 3 All cells in multicellular organisms such as humans have the same set of instructions in the nucleus but can become specialised
cells that form a great variety of shapes and functions. Discuss in your pair and consider an imaginative way of explaining this phenomenon.

Record your work in the table on pages 3, 4 and 5.

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Station Diagram Function Specialised structures

Baseline 1:

cell.

Baseline 2:

cell.

(continued)

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Station Diagram Function Specialised structures

Intermediate 1:

cell.

Intermediate 2:

cell.

(continued)

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Station Diagram Function Specialised structures

Challenge 1:

cell.

Challenge 2:

cell.

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Name Date

B1.2: Cells–unanswered questions

ATP chlorophyll energy glucose protection respiration

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Number of cells in human body Number of bacterial cells in human body

A 3.74 × 1013 1.12 × 1014

B 3.74 × 1012 1.12 × 1013

C 1.12 × 1014 3.74 × 1013

D 1.12 × 1013 3.74 × 1012

Table 1.1

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Name Date

Extra-stretch sheet for Worksheet B1.2:

Cells–unanswered questions
1 The idea that some of the structures in today’s animal and plant cells were once free-living
bacteria is called the endosymbiotic theory. Research the meaning of the terms endo-
and -symbiotic.

2 Some medicinal drugs have been developed to prevent viruses causing damage to human
cells. Carry out some internet research to find out which medicines prevent a virus from
performing the following actions:

a Attaching to a cell membrane.

b Carrying out protein synthesis at the ribosome.

c Using the ATP produced by the mitochondria.

3 A typical cell in a human has a diameter of 10 μm. Assuming that all cells are the same
size, calculate the distance that would be covered if all of the human cells in a human
body were lined up next to each other. Give your answer in kilometres.

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Name Date

Help sheet for Worksheet B1.2:

Cells–unanswered questions
Use the information and activities on this sheet to help you answer the questions on the
corresponding worksheet.

1 Use Figure 1.1 to help you complete the missing word exercise.

Figure 1.1

2 Draw lines between the boxes on the left and the boxes on the right to match the features
of cells with their descriptions.

Term Description
A very thin layer surrounding the cytoplasm of every cell; it controls what
nucleus
enters and leaves the cell.

Tiny structures found in animal cells and plant cells. They are so small
cell wall
that we can only see them with an electron microscope.

A tough layer outside the cell membrane; found in the cells of plants,
mitochondria
fungi and bacteria.

Small structures in a cell, where aerobic respiration releases energy

vacuole
from glucose.

cytoplasm A structure containing DNA in the form of chromosomes.

A fluid-filled space inside a cell, separated from the cytoplasm

ribosomes
by a membrane.

cell membrane The jelly-like substance that forms the ‘background material’ of all cells.

3 The number of bacteria in and on a typical human body is around 112 trillion,
or around 1.12 × 1014.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B2.1

Name Date

B2.1: Drying mangoes

Read the information carefully and use it to help you answer the questions that follow.
Mangoes are a sweet, edible fruit of a tree that grows in many tropical countries. Mangoes can be dried
to enable them to be stored for long periods of time. Traditionally, mangoes are dried by slicing them
into strips and leaving them in the sun (Figure 2.1).

Figure 2.1

When mango tissue dries, water from the mangoes evaporates into the air. The sugars and other
substances in the cells of the mango fruit stay inside the cells. This means that dried mangoes taste even
sweeter than fresh ones.
An even better method of drying mangoes is to use osmosis. The pieces of mango are immersed in a
concentrated sugar solution. Water moves out of the mango cells by osmosis. This method of drying
does not expose the mangoes to such high temperatures as sun-drying. The mangoes lose about 30%
of their mass when they are dried in this way.
Scientists have found that the best conditions in which to dry mangoes by osmosis are to use a 65%
sugar solution, a temperature of 35 °C, mangoes sliced into 5 mm pieces and to leave them in the
solution for six hours.

1 Explain why mangoes that have been dried by leaving them in the sun taste sweeter than
fresh mangoes.

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2 Suggest an explanation for the following statements.

a Water moves out of the mango pieces when they are immersed in a 65% sugar solution.

b The mangoes need to be left in the sugar solution for six hours in order to achieve the
best results.

c This process works best when the mangoes are sliced into pieces 5 mm thick, rather than
left whole.

3 In the spaces below, draw and label what you think a cell from a fresh mango, and a cell
from a dried mango, might look like.

Cell from a fresh mango Cell from a dried mango

4 Dried mango slices can be used in cooking. When the mango pieces are put into water,
they swell up. This happens faster in warm water than in cold water.
a Explain why the mango slices swell up when placed in water.

b Explain why the mango slices swell up faster in warm water than in cold water.

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Name Date

Extra-stretch sheet for Worksheet B2.1:

Drying mangoes
You read earlier in Worksheet B2.1 that:
Scientists have found that the best conditions in which to dry mangoes by osmosis are to use a 65%
sugar solution, a temperature of 35 °C, mangoes sliced into 5 mm pieces and to leave them in the
solution for six hours.
Outline the experiments conducted by scientists that may have led them to this conclusion.

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Name Date

Help sheet for Worksheet B2.1:

Drying mangoes
Use the information and activities on this sheet to help you answer the questions on the
corresponding worksheet.

1 Use the terms concentration and evaporation in your answer.

2 Write rough notes to describe what is happening in the three diagrams in Figure 2.2 to
help you construct your answers to these three sub-questions.

Question part Help diagram Notes

Figure 2.2

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3 Remember that these cells are from a fruit, not a leaf, and that they do not photosynthesise.
Which organelles will they have, and which will they not have?

4 Complete the two paragraphs below, using the following words. You will need to use
one word twice.

higher into kinetic osmosis quickly

a Mango slices swell up when placed into water because the water has a

________________ water potential than the mango tissue. Therefore, water moves

________________ the mango by the process of ________________.

b Mango slices swell up faster when placed into warm water because at higher temperature,

water molecules have more ________________ energy. Therefore, water moves

more ________________ into the mango by the process of ________________.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B2.2

Name Date

B2.2: Diffusion
A group of students is investigating diffusion.
The students know that hydrochloric acid will diffuse through agar jelly. They also know that
universal indicator is green in the neutral agar jelly and will turn red when in contact with
hydrochloric acid.
The students make agar jelly containing universal indicator.
They cut the agar jelly into four cubes as shown in Figure 2.1.

Figure 2.1

1 a Complete Table 2.1 to show the surface area, the volume and the surface area to
volume ratio of each cube. (The surface area to volume ratio is the surface area
divided by the volume, and is usually given with no units.)

Cube A B C D

Length of one side / cm

Surface area / cm2

Volume / cm3

Surface area to volume ratio

Table 2.1

b Describe how the surface area to volume ratio of the cubes varies with the length of
the sides of the cubes.

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2 The students placed each cube into a separate 100 cm3 glass beaker.
They added 50 cm3 of the same hydrochloric acid solution to each beaker and started a timer.

a Explain why the same hydrochloric acid solution was added to each beaker.

b Describe one source of error in this procedure.

3 The students observed the colour change in the cubes. At the moment when a cube turned
completely red, they recorded the time taken.
Describe what you would expect their results to show. Explain any ideas that you have.

4 The cubes in this investigation can be used to model animals. The smaller cubes represent
smaller animals.
A different investigation, which used different substances and a larger range of cube sizes,
gave the following results:

• a cube with side length 0.2 cm took only 1.2 s to completely change colour
• a cube with side length 3.0 cm took more than 1 hour to completely change colour.

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a Use these results to suggest why:

• very small animals can carry out gas exchange, nutrition and excretion by diffusion
directly with their surroundings
• larger animals require organ systems to transport gases, nutrients and wastes to and
from all cells.

b Suggest one advantage and one disadvantage of using agar jelly cubes to model animals.
Advantage

Disadvantage

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Name Date

Extra-stretch sheet for Worksheet B2.2:

Diffusion
1 a When you round a number to put in a table, such as possibly the volume of cube A,
this can affect the accuracy of any calculation that uses that number.
For cube A, try calculating the surface area to volume ratio using a rounded value.
Now calculate the same ratio using a value that is not rounded.
Comment on any difference.

b Can you describe the trend more accurately, rather than just referring to one value
increasing and another increasing or decreasing?

2 a In this investigation, the same volume of acid is added to each beaker.

Each beaker, however, contains a different sized cube.
Can you suggest and explain an improvement to this procedure?

b Can you suggest an improvement to this step?

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c Suggest what will happen to the concentration of acid in the beakers during the
investigation. Explain your suggestion.

3 Waiting for the largest cube to completely change colour can take a very long time.
Sometimes, in the time available in one lesson, the largest cube will not change colour.
For example, after 30 minutes, the largest cube may look like the one below in Figure 2.1.

Figure 2.1

Suggest an improvement to this investigation that would involve getting accurate results
for all cubes in a shorter time.

4 Suggest a method to determine the surface area to volume ratio of an adult human.

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Name Date

Help sheet for Worksheet B2.2:

Diffusion
1 a The surface area of a cube is worked out like this:

area of one face × number of faces

For example, the area of one face of cube B is:
0.5 cm × 0.5 cm = 0.25 cm2
How many faces does a cube have? Think of numbers on a dice.
The volume of a cube is worked out like this:
length of one side × length of one side × length of one side
For example, the volume of cube D is:
2.0 cm × 2.0 cm × 2.0 cm = 8 cm3

Your table should include the numbers found in Table 2.1 below:
Cube A B C D

Length of one side / cm 0.25 2.0

Surface area / cm2 0.375

Volume / cm3 8

Surface area to volume ratio 24 6

Table 2.1

b When describing a trend or pattern, your sentence should be in the form:

as the …………. increases, the …………… [increases or decreases]
What happens to the side length as you go from cube A to cube D?
What happens to the surface area to volume ratio?

2 a Think about the variables that affect diffusion. One of these is mentioned in the
definition of diffusion. That one forms part of this answer.

b Think what will happen if you are pouring liquid into four beakers and can only start the
timer once.

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3 Diffusion takes time because acid particles move slowly through the agar jelly.
What trend will you expect to see in the results for the different sizes of cubes?

4 Humans and other large animals have a breathing system, a circulation system and a
digestive system. Together these organ systems supply all of our cells with oxygen and
nutrients and also remove wastes.
Very small animals do not need these systems.

a What similarity can you see between the results from these cubes and the different
sizes of animals?

b Think about how easy it is to get good results from each investigation. How might
cubes be an advantage over animals?
Think about the shapes of animals. How might cubes be a disadvantage?

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B3.1B

Name Date

B3.1B: Classifying carbohydrates

Carbohydrates are a family of biological molecules that are used for a wide variety of functions in
animals and plants. Two examples of carbohydrates are glucose and starch.
Table 3.1 shows the concentrations of glucose and starch in a sweet potato, which is a type
of vegetable.
Total sugar including reducing sugar / g per 100 g Starch / g per 100 g
0.0 33.5
Table 3.1

1 An uncooked sample of the sweet potato is tested with Benedict’s solution and iodine
solution. Using Table 3.2, identify which set of results would be observed and which
conclusions could be drawn from this investigation.
Benedict’s test Iodine test
Observation Conclusion Observation Conclusion
A red positive red negative
B negative red blue–black red
C blue negative blue–black positive
D positive blue positive blue–black

Table 3.2

Answer: _____

2 Figure 3.1 shows a diagram in which glucose and starch have been classified.
a In the appropriate places on Figure 3.1, add the names of the other carbohydrates
that you have encountered in previous lessons. The names of these carbohydrates are
shown below.
cellulose glycogen maltose sucrose

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Figure 3.1

b On Figure 3.1:
• underline once the carbohydrate that is used for storage in plants
• underline twice the carbohydrate that is used for storage in animals
• circle once the carbohydrate that is used for transport in plants

• circle twice the carbohydrate that is used for transport in animals

• draw a box around the carbohydrate that is used to build cell walls in plants.

3 In the space below, draw and label a simple diagram to show how a molecule of starch is
broken down to release molecules of glucose for use in respiration.

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4 A student wanted to investigate the effect of cooking time on the glucose concentration
of sweet potato. Describe an experiment the student could use to conduct their
investigation. Include in your answer which factors should be kept constant.

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Name Date

B3.2B: Proteins and fats

1 Proteins are made from amino acids.
a Name the chemical elements that are found in all amino acids.

b Name the chemical element that is found in only some amino acids.

2 Name the three chemical elements that are found in all fats and oils.
•
•

3 A student predicts that milk contains protein.

Describe how the student could test this prediction.

4 The student predicts that butter contains fat.

Describe how the student could test this prediction.

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5 Figure 3.1 shows two different types of molecules.

Figure 3.1

Each of the molecules in Figure 3.1 is a type of acid used to make either proteins or fats.
Identify which is which and name the type of molecule.
i Molecule a is ________________ and is used to make ________________.
ii Molecule b is ________________ and is used to make ________________.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B4

Name Date

B4: Comparing washing powders

Your teacher will arrange you into groups of three to do this activity. Read the information
carefully and use it to help you answer the questions that follow.
Shortly after enzymes were discovered in the early 20th century, scientists began to consider their
practical uses. One of the earliest industrial applications of enzymes was in biological washing powders
(Figure 4.1).

Figure 4.1

Washing powders contain a range of enzymes, including amylase, proteases and lipases. These help
to break down some of the molecules found in blood, food and plant-based stains.
You will plan an investigation to compare the effectiveness of two brands of washing powder by
measuring their ability to break down starch, protein and oil.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B4

In this task, you will work in groups of three to investigate how scientists compare the claims of
manufacturers. The roles are as follows:
• Background researcher–you will be asked to use the internet to research relevant information
related to this investigation, and then answer some related questions.
• Method planner–you will be provided with a list of equipment and asked to plan how to conduct
the investigation.
• Quality control officer–you will consider how to make the investigation that you plan of the
highest scientific quality.
Decide who will take on which role. You may decide to undertake a role that you feel is a strength
of yours. Alternatively, you may wish to challenge yourself by taking on a role that is an area you
wish to develop.
When you have each completed your worksheet, you will come together as a group to collectively
evaluate (review) the work that you have produced. There will also be some further questions for
you to answer together.

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Name Date

Comparing washing powders:

Evaluation task
You should have provided feedback on each other’s work, before completing this final worksheet.
You should attempt the following questions together.
Scientists used a similar method to yours to investigate the effectiveness of Enzymaway
and Magiclear. Answer the following questions as a group. There will be an opportunity for you
to reflect on how the earlier task sheets helped you at the end of this exercise.

1 The scientists’ results are shown in Figure 4.2.

Figure 4.2
a Use Figure 4.2 to complete Table 4.1.

Washing Width of zone of digestion / mm

Substance
powder brand Well 1 Well 2 Well 3 Mean

Starch A

Starch B

Protein A

(continued)

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Washing Width of zone of digestion / mm

Substance
powder brand Well 1 Well 2 Well 3 Mean

Protein B

Lipid A

Lipid B

Table 4.1

b State the type of graph that the scientists should use to display their results.
Explain your choice.

2 In addition to the tests shown in Figure 4.2, the scientists also used control experiments in
their investigation. They did this by boiling washing powder solution and adding this to
similar wells that were cut into the plates.
a Explain why no zone of digestion should be seen in these control experiments.

b The scientists found that the control wells did have a very small halo around them after
the incubation period. Suggest why this has happened and how they should deal with it.

3 A learner carries out some research and finds that one brand of biological washing
powder contains the enzymes inside gel beads. Suggest one reason why enzymes in
biological washing powders are often added to the detergent in this form instead of
powdered form.

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Name Date

Comparing washing powders:

Method planner
Read the information carefully and use it to help you answer the questions that follow.
A manufacturer claims that it has produced a type of washing powder, called Enzymaway,
that is better than the most common brand on the market, Magiclear.
Your task is to plan a method that can be used to assess this claim. For the purposes of this
investigation, three pairs of agar plates are provided.

1 The agar in one pair of plates contains milk powder, which contains a white powder
called casein. When this protein is broken down, the agar becomes colourless.

2 The agar in another pair of plates contains starch powder and iodine solution, to show
the presence of starch. The agar is blue–black in colour at first. When the starch is broken
down, the agar becomes red–brown.

3 The agar in the final pair of plates contains vegetable oil and a small volume of alkali
called sodium hydrogencarbonate. It also contains universal indicator solution. When the
oil is broken down, the agar becomes red.
In addition, you are provided with the following items of equipment:

• cork borer for cutting small circles of agar • test-tubes

• dropping pipettes • incubator set at 37 °C
• stop clock • ruler with millimetre measurements
• graph paper • bunsen burner
Clue: determine the size of the circles of colour-change to assess the activity of the washing powder.

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Write down the feedback comments you received from your group members here:

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Name Date

Comparing washing powders:

Quality controller
Read the information carefully and use it to help you answer the questions that follow.
A manufacturer claims that it has produced a type of washing powder, called Enzymaway,
that is better than the most common brand on the market, Magiclear.
Your task is to consider key aspects of experimental technique such as accuracy,
validity and reliability.
• Accuracy is a measure of how close the measured value in an experiment is to the actual value.
• Validity is a measure of the certainty that the change made in the experiment (to the independent
variable) is responsible for any measured change in the dependent variable.
• Reliability is a measure of how consistent the results are when the experiment is repeated.
Your task is to record how these aspects of experimental technique could be improved.
To help you, three clues are provided below.

1 Accuracy
Clue: which is better to use, a ruler or graph paper? Why?

2 Validity
Clue: consider factors that affect enzyme activity, as well as volumes and time.

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3 Reliability
Clue: consider repeats and a mean.

Write down the feedback comments you received from your group members here:

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Name Date

Comparing washing powders:

Background researcher
Read the information carefully and use it to help you answer the questions that follow.
A manufacturer claims that it has produced a type of washing powder, called Enzymaway,
that is better than the most common brand on the market, Magiclear.
Your task is to carry out research into the use of washing powders in order to help you answer
four questions.
When you have answered these questions, you will receive feedback from the other members of
your group. A space is provided on the next page to allow you to reflect on these suggestions.
Most biological washing powders contain a range of enzymes that remove stains from dirty clothes.

1 Explain why a biological washing powder should contain more than one enzyme in order
to wash clothes that have stains such as dried egg and blood.

2 Many biological washing powders work best at temperatures between 40 °C and 50 °C.
Explain why these biological washing powders are not as effective in a very hot wash
at 90 °C.

3 Some washing powders contain enzymes extracted from bacteria found in hot water
springs. Suggest one advantage of using enzymes from these bacteria in washing powders.

4 Many washing powders are able to wash clothes effectively at 25 °C.

Suggest one advantage of this.

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Write down the feedback comments you received from your group members here:

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B5.1B

Name Date

B5.1B: Leaves under attack

Plants grow leaves to help them to make glucose by photosynthesis. Unfortunately for the plants,
other organisms also want this glucose and other nutrients stored in the leaves.

Instructions
Go outside and find at least three different leaves that seem to have been attacked by another
organism. For example, you might be able to find:
• leaves with little galls (growths) on them, which have been caused by insect larvae
• leaves with holes in them, suggesting they have been eaten by something
• leaves with mould growing on them, showing that a fungus is feeding on them
• leaves with tunnels inside them (the tunnels might look like white or brown trails on the leaf),
showing where a larva has been eating the inside of the leaf
• rolled-up leaves, perhaps with an insect larva inside them.

1 In the space below, make a large, labelled drawing of one of the leaves that has been
affected in some way by another organism.
In your diagram, be sure to:

• draw the leaf as large as possible using a sharp pencil

• not include any shading
• label the different parts of the leaf
• label the damage to your leaf.

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2 Calculate the magnification of your drawing. Remember to divide the size of your
drawing by the actual size of the leaf.

3 Find out what has happened to your leaf and record your findings below. You could try
looking it up in the library or searching on the internet. Use your own words to write a
summary of the information that you find.

4 Leaves are useful for other organisms because:

• they contain a lot of starch and protein
• they are thin, which makes them easy to eat or to bend
• they have a large surface area, which makes it easy for fungi to grow over them.

a Explain how two of these features are related to the leaf’s function.

b Explain how these two features helped the organism make use of your leaf.

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Name Date

B5.2C: Photosynthesis
The water plant, Elodea canadensis, or pondweed, can be used to study photosynthesis.
Pondweed grows under water and has many small leaves arranged along long stems.
Figure 5.1 shows how pondweed can be used in a photosynthesis investigation.

Figure 5.1

When the pondweed is photosynthesising, bubbles can be seen rising from the pondweed as shown
in Figure 5.1.

1 Describe what is meant by the word photosynthesis.

2 Write a balanced symbol equation for photosynthesis.

3 a When the plant is doing photosynthesis, name the gas that we assume is in the bubbles
in Figure 5.1.

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b i Suggest what other gas could be present in the bubbles.

ii Explain where this other gas could come from.

4 A student carried out an investigation using the pondweed.

• A lamp was used as a light source for the pondweed.
• The distance between the lamp and the pondweed was changed.
• The number of bubbles was counted for 1 minute at each distance.
The results are shown in Table 5.1.

Number of bubbles in 1 minute

Distance between Experiment 1 Experiment 2 Experiment 3 Average

lamp and
pondweed / cm

20 105 96 99

30 84 91 79

40 55 60 54

50 38 44 40

60 35 39 32

70 27 24 20

80 15 12 14

Table 5.1

a Complete Table 5.1 by calculating the averages.

Round your averages to the nearest whole number.

b Plot a graph of the average results on the graph grid on the next page.
Put the independent variable on the x-axis.
Join the points using straight lines.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B5.2C

c Explain the trend shown in your graph.

d When the student was doing this investigation, a thick piece of transparent glass was
placed between the lamp and the beaker containing the pondweed.
Explain the purpose of this piece of glass.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B5.2C

e The student thinks that the accuracy of the experiment could be improved by
measuring the volume of gas collected in the test-tube rather than counting bubbles.
The student suggests that increasing the time to collect the gas at each distance would
also improve accuracy.
Discuss whether these changes would give more accurate results:

i Measuring the volume.

ii Increasing the time.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B6

Name Date

B6: Essential amino acids

Proteins are made of amino acids. There are 20 different amino acids. The way in which the amino
acids are linked together in a chain determines the kind of protein that they form. Even if just one
amino acid is different, it makes a different protein.
We get our amino acids in the food that we eat. Proteins in the food are broken down into amino
acids in the digestive system, and then absorbed into the blood. The blood delivers them to body
cells. Each cell can then make its own proteins, by linking together amino acids.
Our body is able to change some amino acids into other amino acids. However, there are some
amino acids that we cannot obtain in this way. We must actually eat that particular kind of amino
acid: we cannot make it from other amino acids. These are called essential amino acids. There are
eight essential amino acids. They are:

isoleucine leucine lysine methionine

phenylalanine threonine tryptophan valine

Table 6.1 shows:

• the mass in grams of these amino acids that we need each day
• the percentage of the protein in different foods that is made up of each essential amino acid
• the amount of protein in 100 g of the food.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B6

Percentage of protein in these foods that is made up of each essential amino acid

Recommended

Corn (maize)

White beans
Wheat flour
amount per
Amino acid

White rice

potatoes
day / g

Sweet

Beef

Milk
Egg
Tryptophan 0.50 0.70 1.40 0.70 1.80 0.80 3.10 3.80 2.30

Phenylalanine 0.56 3.10 5.90 6.10 10.9 2.50 11.2 13.6 7.70

Leucine 1.40 3.00 8.00 12.0 17.0 2.60 22.4 21.0 15.9

Isoleucine 1.40 3.00 5.20 4.10 11.3 2.20 14.3 15.7 10.3

Lysine 1.60 2.50 3.20 4.10 14.7 2.10 23.9 15.3 12.5

Valine 1.60 4.50 5.50 6.80 12.1 3.40 15.1 17.7 11.7

Methionine 0.22 1.10 1.80 2.10 2.00 0.80 6.80 7.40 1.90

Threonine 1.00 2.50 3.50 4.50 8.50 2.10 12.5 12.0 7.40

Total protein content in

2.70 12.0 10.9 19.8 4.50 27.6 23.8 16.0
100 g of food / g

Table 6.1
Use this information and your wider knowledge to answer the following questions.

1 Explain what is meant by an essential amino acid.

2 Which of the foods shown in the table has the greatest amount of protein per 100 g of food?

3 Use the data in Table 6.1 to calculate:

a the mass of leucine in 100 g of white rice

g
b the mass of lysine in 100 g of beef.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B6

4 Use the information in Table 6.1 to explain why people who do not eat meat, eggs or milk
need to plan their diet carefully to ensure that they get enough essential amino acids in
their food.

5 Describe how the data in Table 6.1 should be represented in a graph. You may draw
sketches in the space below to help you with your answer.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B6

Name Date

Extra-stretch sheet for Worksheet B6:

Essential amino acids
1 Undertake research online to find out more about phenylketonuria (PKU), a disorder
that leads to the accumulation of the essential amino acid phenylalanine in the blood.
Record your findings here:

2 Which of the foods shown in the table has the least amount of protein per 100 g of food?

3 The figure provided for white rice applies to cooked white rice. Raw white rice contains
7 g of protein per 100 g.
Use this information to calculate the percentage change in protein content caused by
cooking rice.

4 Undertake research online to find out more about amino acid or protein deficiency.
Record your findings here:

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B6

5 Draw a bar chart to compare the total protein content in 100 g of different foods.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B6

Name Date

Help sheet for Worksheet B6:

Essential amino acids
Use the information and activities on this sheet to help you answer the questions on the
corresponding worksheet.

1 Refer to the third paragraph of the information on the first page of the worksheet to
answer this question.

2 Refer to the final row in the table to answer this question.

3 The following worked example shows how to calculate the number of grams of leucine in
100 g of wheat flour:

The table shows that a 100 g sample of wheat flour contains 12.0 g of protein.
The table also shows that 8.00% of this protein is leucine.
We can use this information to calculate the number of grams of leucine in 100 g of wheat flour,
like this:
Mass of protein in 100 g of wheat flour is 12.0 g.
8% of this protein is leucine.
So, the mass of leucine in 100 g of wheat flour is
8
× 12.0 = 0.96 g
100

4 Draw a circle around all foods that are not meat, eggs or milk.

5 The best option to display these data would be as a bar or pie chart. Why would a line
graph not be as useful?

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B7C

Name Date

B7C: The route of water through a plant

Figure 7.1 shows an outline of part of a plant.

Figure 7.1

1 On the diagram, label the position of each of the following tissues and cells.
mesophyll cells root cortex cells root hair stomata xylem

2 Write a number next to each part that you have labelled to show the sequence in which
water passes through them.

3 Use a blue pen to circle each part you have labelled in which the water travels as a liquid.

4 Use a red pen to circle each part you have labelled in which the water travels as a gas.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B7C

5 Fill in the gaps with suitable words or phrases to explain the mechanism that is responsible
for the movement of water in xylem vessels.
Water moves up through a plant as the result of _______________, which is the loss of
water vapour through the _______________ in the leaves. This produces a tension, called
_______________, which pulls columns of water up through the _______________.

As water vapour is lost from the leaves, this reduces the _______________ inside the air spaces
in the leaf _______________ layers. This causes water to evaporate from the surface of the
mesophyll cells. This _______________ the water potential inside the mesophyll cells, producing
a water potential _______________ from the xylem vessels in the leaf into the cells. Water
therefore moves out of the xylem vessels, into the mesophyll cells. It moves into these cells
by _______________.

This removal of water from the upper parts of the xylem vessels causes the water potential at
their tops to be lower than the water potential at their bases. Water is therefore drawn up
through the xylem vessels in a continuous column. The column remains continuous because
water molecules are attracted to each other by _______________, and to the walls of the xylem
vessels by _______________.

6 Outline how you could investigate the effect of an increase in temperature on the rate
of transpiration.
In your answer, refer to:
• the independent variable and how you will change it
• the dependent variable and how you will measure it
• which variables will be standardised in the investigation and how.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B7C

The next questions are about transport in humans.

7 Tick ( ) the box next to the correct statement.
Contractions of the heart
A The left side of the heart contracts before the right side of the heart.
B Both sides of the heart contract at the same time.

8 Tick ( ) the box next to the correct statement.

During exercise
A The heart beats more quickly during exercise because you need to breathe faster.
B The heart beats more quickly during exercise because the muscles need more oxygen.

9 Tick ( ) the box next to the correct statement.

Coronary heart disease
A Coronary heart disease is caused by blockage of the arteries that supply the heart muscle with
oxygenated blood.
B Coronary heart disease is caused by blockage of the arteries that supply the brain with
oxygenated blood.

10 Tick ( ) the box next to the correct statement.

The valves between the atria and ventricles
A When the ventricles contract, these valves are forced closed by the pressure of the blood.
B When the atria contract, these valves are forced closed by the pressure of the blood.

11 Tick ( ) the box next to the correct statement.

The muscles in the heart
A The wall of the left ventricle is thicker than the wall of the right ventricle because the left
ventricle contains oxygenated blood.
B The wall of the left ventricle is thicker than the wall of the right ventricle because the left
ventricle needs to produce a higher pressure when the muscle contracts.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B8

Name Date

B8: Adaptations of the Note: this page should be printed

single-sided.
cholera bacterium
Your teacher will arrange you into groups of four to do this activity. Read the information carefully
and use it to help you answer the questions that follow.
Cholera is a serious disease of the alimentary canal that causes severe diarrhoea, dehydration and often
death. It is associated with ingesting water contaminated with sewage. This often occurs after natural
disasters; Figure 8.1 shows a young child being treated in the Philippines after a typhoon.

Figure 8.1

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B8

As a group of four, you will carry out research and prepare a report to the local health authority to
explain why common methods of food hygiene are usually not sufficient to avoid the transmission
of cholera between people.
In this task, you will work individually to investigate one issue each, using your coursebook and the
internet. First, decide who will research which issue. You may decide to investigate an issue that is
of particular interest to you. Alternatively, you may wish to challenge yourself by deciding to
research an issue that is an area you wish to develop.
Next, individually carry out your research into the adaptations of the cholera bacterium and
complete your own worksheet.
Then, come together as a group to evaluate (review) the work that you have produced using the
instructions below.

1 Take it in turns, for around 30 to 60 seconds each, to describe what you have found out.

2 Decide how your group can present your research in the form of a factsheet on a single
side of A4 paper.

3 Attach your work to the wall and listen to your teacher’s instructions. They will inform
you how you will give feedback to other groups.

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----------------------------------------------------------------------------------------------------------------------------

Note: this page should be printed

Issue 1 single-sided.

Consider the statement below and carry out research to explain this observation.
Mucus and hydrochloric acid in the stomach do not prevent cholera.

----------------------------------------------------------------------------------------------------------------------------

Issue 2
Consider the statement below and carry out research to explain this observation.
Causing diarrhoea is an advantage for the cholera bacterium.

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Issue 3
Consider the statement below and carry out research to explain this observation.
Memory cells are not formed that recognise cholera.

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Issue 4
Consider the statement below and carry out research to explain this observation.
Cholera bacteria sense an increase in their surrounding temperature when they enter a host.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B8

Support sheet for Worksheet B8:

Adaptations of the cholera bacterium
1 Food hygiene methods for prevention of cholera could include:
• washing hands regularly, especially after visiting the toilet
• making sure all eating and cooking utensils are clean
• correct storage of food–refrigeration / freezing / defrosting methods
• ensuring food is fully cooked
• ensuring raw food is washed in clean, uncontaminated water
• ensuring drinking water is not contaminated with sewage
• protecting food and preparation areas from flies
• not allowing anyone with cholera symptoms to prepare or handle food for others.

2 Factsheets should be appealing to look at and may be coloured and illustrated.

3 Feedback can be structured as a ‘sandwich’ with:

• the first layer–what is good about the presentation and why it is good
• the middle layer–what could be made better and how it could be improved
• the last layer–some final positive and encouraging comments.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B9

Name Date

B9: Respiration equations

1 This equation represents a type of respiration.

C6H12O6 + 6O2 → __CO2 + __H2O

a What type of respiration is shown by the equation?

b How many carbon atoms are there on the left-hand side of the equation?

c How many oxygen atoms are there on the left-hand side of the equation?

d Balance the equation by writing numbers in the two spaces in the equation above.
e Explain what is meant by the term balanced equation.

2 Anaerobic respiration is another type of chemical reaction that occurs in humans.

a Write the word equation for anaerobic respiration in humans.

b Complete this sentence using a word from the list below.

credit debt gain loss

When the product of anaerobic respiration builds up in muscles, it can

cause oxygen __________.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B9

Name Date

Extra-stretch sheet for Worksheet B9:

Respiration equations
1 Carry out research online to find out about the quantity of energy released from aerobic
and anaerobic respiration. Are they the same? Make sure to write anything you find in
your own words and do not just copy. Use the space below to write your findings.

2 Carry out further research online to find out the importance of anaerobic respiration in humans.
Use the space below to write your findings.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B9

Name Date

Help sheet for Worksheet B9:

Respiration equations
1 Look closely at the equation.
Note that:
a oxygen is involved in this chemical reaction
b, c the subscript number after a letter indicates the number of atoms present
d the large number in front of a molecule means that there is this number of molecules
in the reaction
e you should refer to ‘sides of the equation’ to answer this question.

2 Remember that:
a oxygen is not involved in this chemical reaction
b you need the same word that is used when you owe money to someone.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B10

Support sheet for Worksheet B10:

Investigating reaction time
Table should be ruled with column headers for:
person catching / hand used / left drop distance five attempts average drop distance
name or initials or right with unit with unit.

Table should be completed neatly with no units in the body of the table.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B11.1

Name Date

B11.1: Analysing an investigation

into pollination
Your teacher will arrange you into groups of four to do this activity. Read the information carefully
and use it to help you answer the questions that follow.
An investigation was carried out into the effects of self-pollination and cross-pollination in plants of
American ginseng, Panax quinquefolius (Figure 11.1).

Figure 11.1

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B11.1

Before the flowers opened, flowers on selected plants were covered with bags made of a very fine mesh.
When each flower opened, the bags were taken off and the stamens were carefully removed.
For some of the flowers, pollen from the removed anthers was then dusted onto the stigma of the
same flower. These were the self-pollinated flowers.
For other flowers, pollen from a different flower was dusted onto their stigmas. These were the
cross-pollinated flowers.
The flowers were then covered again with the mesh bags and allowed to produce seeds. The seeds were
collected and sown and allowed to grow for two years. The leaf area and stem height of each plant were
measured. The mean values for the seedlings grown from self-pollinated plants, and those grown from
cross-pollinated plants, were calculated.
The results are shown in the bar charts in Figure 11.2.

Figure 11.2

Instructions
1 Your teacher will arrange you into groups of four. You must first work in two pairs for
five minutes. Each pair should answer both question A and question B.

2 Swap partners and discuss your original answers for two to three minutes. Write down
any improvements on your first answers to questions A and B.

3 Finally, join together in your original group of four to decide on your final answers.
Swap your answers with another group of four to be peer assessed.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B11.1

First draft Note: this page should be printed

single-sided.

Question A – method analysis

Explain why:

a the flowers were covered with bags before the flowers opened

b the bags were made of fine mesh, rather than polythene

c the stamens were removed from all of the flowers.

Write any improvements to be made here:

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B11.1

First draft
Question B – data analysis
Describe and explain the results for the self-pollinated and cross-pollinated plants.
(Remember to quote figures from the graphs in your answers.)

Write any improvements to be made here:

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B11.1

Final answer
Group members’ names:

Question A – method analysis

Question B – data analysis

Space for peer assessment

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B11.2

Name Date

B11.2: HIV and AIDS

Table 11.1 shows the numbers of people in seven countries living with HIV or AIDS in the past
12 months.

Number of people living Percentage of adults living Deaths due to AIDS

Country
with HIV / AIDS with HIV / AIDS

A 6500 2.8 fewer than 500

B 2000 0.9 fewer than 100

C 14 000 0.2 fewer than 200

D 44 000 0.7 1700

E 120 000 1.8 5800

F 30 000 1.8 1600

G 13 000 1.5 fewer than 1000

Table 11.1

1 Which country had the highest percentage of adults living with HIV or AIDS?

2 Which country had the greatest number of people living with HIV or AIDS?

3 Calculate the total number of people in countries A–G living with HIV or AIDS.

4 Suggest how making people more aware of HIV and AIDS could help these
numbers decrease.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B11.2

Name Date

Extra-stretch sheet for Worksheet B11.2:

HIV and AIDS
1 Five years ago, the number of people living with HIV or AIDS in country B was 1150.
Calculate the percentage change.

2 In some countries, the number of people with HIV or AIDS is expressed as a number
per 100 000 people. Suggest why.

3 Express your answer to question 3 on the original worksheet in standard form to two
significant figures.

4 Carry out some research online to investigate the functions of medicinal drugs that have
been developed to minimise the transmission of HIV from an infected person to others.
Use the space below to record your findings.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B11.2

Name Date

Help sheet for Worksheet B11.2:

HIV and AIDS
Use the information and activities on this sheet to help you answer the questions on the
corresponding worksheet.

1 Use data from the third column to help you with this question.

2 Rank order the countries from the one with the largest to the one with the smallest
number of adults living with HIV or AIDS.

3 Check your answer by adding up all of the numbers again.

4 List the ways in which HIV can be transmitted from person to person.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B14.1

First, work on your own to plot a line graph to show these results.

Instructions:
1 In your group of four, work in two pairs for five minutes to answer three questions
related to the graphs you have drawn.

2 Next, swap partners, exchange your thoughts for two to three minutes and write down
any improvements.

3 Finally, join together to decide on a final answer to be peer assessed by another group.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B14.1

----------------------------------------------------------------------------------------------------------------------------

Note: this page should be printed

First draft single-sided.

Question A
Describe and explain what was happening during the time period 0–2 hours.

Write any improvements to be made here.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B14.1

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First draft
Question B
Describe and explain what was happening during the time period 6–10 hours.

Write any improvements to be made here.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B14.1

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First draft
Question C
Describe and explain what was happening during the time period 12–18 hours.

Write any improvements to be made here.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B14.1

Final answer
Group members’ names:

Question A
0–2 hours:

Question B
6–10 hours:

Question C
12–18 hours:

Space for peer assessment:

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B14.2A

Name Date

B14.2A: Food webs

Table 14.1 gives facts about some organisms.

Name of organism Facts about the organism

snail an invertebrate herbivore

meadow grass a green plant

fox a mammal that preys on smaller mammals

mouse a small herbivorous mammal

blue tit a bird that feeds on insects and snails

stoat a small mammal that eats snails and other small mammals

aphid an insect herbivore

Table 14.1

1 Use the information in Table 14.1 to complete the food web in Figure 14.1.
Two organisms have been done for you.

Figure 14.1

2 In the food web, state what is represented by the arrows.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B14.2A

3 In this food web, name:

a one producer

b one primary consumer

c one secondary consumer

d one tertiary consumer

e one prey organism

f one predator organism.

4 State the source of energy for this food web.

5 Table 14.1 contains animals described as herbivores and carnivores.

Describe what is meant by these terms.
Herbivore

Carnivore

6 Write one food chain that contains four organisms in this food web.

__________________ __________________ __________________ ___________________

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B14.2B

Name Date

B14.2B: Food webs

Table 14.1 gives facts about some organisms.

Name of organism Facts about the organism

snail an invertebrate herbivore

meadow grass a green plant

fox a mammal that preys on smaller mammals

mouse a small herbivorous mammal

blue tit a bird that feeds on insects and snails

stoat a small mammal that eats snails and other small mammals

aphid an insect herbivore

Table 14.1

1 Use the information in Table 14.1 to complete the food web in Figure 14.1.

Figure 14.1

2 In the food web, state what is represented by the arrows.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B14.2B

3 In this food web, name:

a one producer

b one primary consumer

c one secondary consumer

d one tertiary consumer

e one prey organism

f one predator organism.

4 State the source of energy for this food web.

5 Table 14.1 contains animals described as herbivores and carnivores.

Describe what is meant by these terms.
Herbivore

Carnivore

6 Write one food chain that contains four organisms in this food web.

__________________ __________________ __________________ ___________________

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B14.2B

7 a State the number of trophic levels in this food web.

b Name one organism that occupies two trophic levels.

c Explain the advantage to this organism of occupying more than one trophic level.

d Energy is lost between trophic levels.

Describe one way that energy is lost.

8 In the area where the organisms in this food web live, there are other organisms
called decomposers.

a Describe what is meant by the term decomposers.

b Name one type of organism that is only visible under a microscope and is classed
as a decomposer.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B14.2C

Name Date

B14.2C: Food webs

Table 14.1 gives facts about some organisms.

Name of organism Facts about the organism

snail an invertebrate herbivore

meadow grass a green plant

fox a mammal that preys on smaller mammals

mouse a small herbivorous mammal

blue tit a bird that feeds on insects and snails

stoat a small mammal that eats snails and other small mammals

aphid an insect herbivore

Table 14.1

1 Use the information in Table 14.1 to construct a food web in the space below.

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2 In a food web, state what is represented by the arrows.

3 In this food web, name:

a one producer

b one primary consumer

c one secondary consumer

d one tertiary consumer

e one prey organism

f one predator organism.

4 State the source of energy for this food web.

5 Table 14.1 contains animals described as herbivores and carnivores.

Describe what is meant by these terms:
Herbivore

Carnivore

6 Write one food chain that contains four organisms in this food web.
__________________ __________________ __________________ ___________________

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7 a State the number of trophic levels in this food chain.

b Name one organism that occupies two trophic levels.

c Explain the advantage to this organism of occupying more than one trophic level.

d Energy is lost between trophic levels.

Describe one way that energy is lost.

8 In the area where the organisms in this food web live, there are other organisms
called decomposers.
a Describe what is meant by the term decomposers.

b Name one type of organism that is only visible under a microscope and is classed
as a decomposer.

9 Many humans eat the meat of chickens or products from chickens, such as eggs.
Most chickens are farmed and fed on crop plants such as corn.
a Construct a food chain to show this information in the space below.

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b Humans can also eat corn.

Use this information to explain why a larger population of humans could be sustained on
crop plants rather than farmed animals.

c Humans are classed as omnivores. This means humans can get energy from eating
plants or animals.
The majority of animals that are farmed for meat for human food are primary consumers.
Examples include chickens and sheep.
Suggest why secondary consumers are very rarely farmed for meat for human food.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B15.1

Name Date

B15.1: Indicator species

A quick way of assessing whether or not a stream or pond is polluted is to find out what
is living there.
Some invertebrates (animals without backbones) live only in unpolluted water where there is a
lot of oxygen. Others are able to live in polluted water. They are called indicator species. Some of
these organisms and the degree of pollution they can live in are shown in Figure 15.1.

Figure 15.1

Table 15.1 shows the invertebrates that were found in two freshwater rivers.
Invertebrate Number in River A Number in River B
Stonefly larvae 0 15
Mayfly larvae 0 6
Caddis larvae with cases made of stones 0 1
Caddis larvae with cases made of sticks and leaves 0 2
Freshwater shrimps 0 30
Leeches 3 12
Snails 31 59
Rat-tailed maggots 92 0
Bloodworms 103 0

Table 15.1

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Use this information and your wider knowledge to answer the following questions.

1 Suggest how indicator species are chosen by scientists.

2 Suggest how the sampling of the two rivers must be carried out in order to allow a
valid comparison.

3 Which river was more polluted? Explain your answer.

4 Suggest what may have caused this pollution. Explain your answer.

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Name Date

Extra-stretch sheet for Worksheet B15.1:

Indicator species
A group of learners carried out some fieldwork on one of the rivers. They wanted to learn more
about the effect of a tourist resort sited on the riverbank on the levels of water pollution.
The learners chose five sites along the river and assessed the population size of four indicator
species. The tourist resort is positioned between site 2 and site 3.

1 Undertake research online to find out more about the specific types of pollution that
threaten the biodiversity of freshwater habitats. Record your findings in the space below.

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The learners plotted their data on a graph, shown in Figure 15.2.

Figure 15.2

2 The number of freshwater shrimps decreased from 75 at site 2 to 15 at site 3. Calculate the
percentage decrease of this population between these two sites. Record your findings in
the space below.

3 The learners found that there were large masses of algae growing in the stream after site 2.
Use Figure 15.2 to suggest an explanation for this finding and explain the difference in
indicator species between site 2 and site 3.

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4 Suggest two reasons why surveying indicator species is preferable to using chemical
analysis to measure water pollution levels.

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Name Date

Help sheet for Worksheet B15.1:

Indicator species
Use the information and activities on this sheet to help you answer the questions on the
corresponding worksheet.

1 Use the terms presence and absence in your answer.

2 A valid comparison is only possible if all other factors that may have an effect on the
numbers of organisms counted are the same between the two samples. What are examples
of these factors?

3 The data show that River A is more polluted, but how can you tell?

4 Undertake research online to help you with this question, specifically looking into
problems caused by the overuse of fertilisers. Record your findings below.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B15.2C

Name Date

B15.2C: Deforestation
1 Describe what is meant by the term deforestation.

2 One of the negative effects of deforestation is reduced biodiversity.

a Describe what is meant by biodiversity.

b State two other negative effects of deforestation.

i
ii

3 Figure 15.1 shows the extent of deforestation in some countries in 2021.

Figure 15.1 (Source: earth.org/deforestation-facts)

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: BIOLOGY WORKSHEET B15.2C

a One of the major causes of deforestation in Brazil is increasing global demand for beef.
Explain how increasing demand for beef causes deforestation.

b Use Figure 15.1 to estimate how many times more forest area was lost in Brazil than
in Laos in 2021.
Show your working.

c The reasons for deforestation vary between countries. Suggest one other
explanation for the large differences shown in Figure 15.1. Give an example
to back up your suggestion.
Reason:

Example:

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4 Many people around the world who lead protests against deforestation live in countries
where deforestation already happened hundreds of years ago. Deforestation has now
stopped in these countries, and tree planting is happening in many areas.
Discuss whether or not it is fair for people from these countries to protest about the
deforestation activities in other countries.

5 In 2021 at a conference on deforestation, 141 countries agreed to a target. The target was
to ‘halt and reverse forest loss by 2030’.
Some countries said they had committed to do this before the conference in 2021.
Figure 15.2 shows the area of forest lost each year in Indonesia from 2002 to 2021.

Figure 15.2

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Use information in Figure 15.2 and in the paragraph above to discuss whether Indonesia
appeared in 2021 to be committed to reducing deforestation.

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