Science questions, chapter 2

Nama / NameKelas / ClassTarikh / Date

Ecosystem

44 marks. Use Practice to check each answer as you go, or Exam to answer everything against the clock first.

Section A: objective questions

12 marks

Choose the best answer for each question.

Question 1

Which organism is a producer?

Caterpillar
Cabbage
Fox
Mushroom

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A producer makes its own food by photosynthesis. Cabbage is a green plant. The caterpillar and fox are consumers and the mushroom is a decomposer.

For the teacher: Remembering, low difficulty, standard 2.1.1

Textbook p. 22

Question 2

What is the role of a decomposer in an ecosystem?

To make food from sunlight
To hunt primary consumers
To store carbon in the body tissues of animals
To break down dead plants and animals into simpler materials

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Decomposers such as bacteria and fungi break down dead organisms into simple materials and nutrients (saprophytism).

For the teacher: Remembering, low difficulty, standard 2.1.1

Textbook p. 22

Question 3

Why does the amount of energy decrease along a food chain?

Some energy is used for movement and respiration, and some is lost as heat and in faeces
Producers keep all the energy for themselves
Decomposers take energy from the Sun
Energy is destroyed when an animal is eaten

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Organisms use energy to move and respire, and lose energy as heat and in undigested food or faeces, so less is passed to the next level.

For the teacher: Understanding, medium difficulty, standard 2.1.2

Textbook p. 24

Question 4

Which food chain is written correctly?

Snake → Frog → Grasshopper → Grass
Grass → Snake → Frog → Grasshopper
Grass → Grasshopper → Frog → Snake
Frog → Grass → Snake → Grasshopper

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A food chain starts with the producer and the arrows point towards the organism that eats, in the direction of energy flow.

For the teacher: Understanding, low difficulty, standard 2.1.2

Textbook p. 24

Question 5

Which process releases oxygen into the atmosphere?

Respiration by animals
Photosynthesis by green plants
Decay by bacteria
Respiration by plants

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Photosynthesis absorbs carbon dioxide and releases oxygen. The other three processes use oxygen and release carbon dioxide.

For the teacher: Remembering, low difficulty, standard 2.2.1

Textbook p. 26

Question 6

How do the roots of plants help in the water cycle?

They release water vapour into the air through respiration
They make rain fall faster
They convert water into oxygen
They absorb water from the soil and hold the soil to prevent erosion

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Roots absorb water that is later released by transpiration, and they hold the soil tightly so that water flows more slowly and soil erosion is prevented.

For the teacher: Understanding, medium difficulty, standard 2.2.2

Textbook p. 25

Question 7

A pond has dragonflies, fish, tadpoles and water snails. All the tadpoles in the pond are called a ______.

population
community
species
ecosystem

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A population is a group of organisms of the same species living in the same habitat. A community is made up of populations of different organisms.

For the teacher: Understanding, medium difficulty, standard 2.3.1

Textbook p. 28

Question 8

A remora fish attaches to a shark and feeds on scraps of the shark's food. The shark is not harmed. What type of interaction is this?

Mutualism
Parasitism
Commensalism
Competition

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Only the remora benefits and the shark is neither harmed nor helped, so this is commensalism.

For the teacher: Applying, medium difficulty, standard 2.3.3

Textbook p. 34

Question 9

In an experiment, most woodlice moved to the partition that contained water and few went to the partition with anhydrous calcium chloride. What does this show?

Woodlice prefer a dry place
Woodlice prefer a damp place
Woodlice prefer a bright place
Woodlice prefer a hot place

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Anhydrous calcium chloride keeps the air dry, so the woodlice that gathered over the water chose the damp (humid) place.

For the teacher: Understanding, medium difficulty, standard 2.3.1

Textbook p. 31

Question 10

Which is a weakness of biological control?

It pollutes the air and soil with chemicals
It harms human health
It is always more expensive than pesticides
It takes a long time before the effect is seen

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Biological control is slow, and a newly introduced species may upset the balance of the ecosystem. It does not use chemicals and usually costs less.

For the teacher: Understanding, medium difficulty, standard 2.3.3

Textbook p. 36

Question 11

Diagram 1 shows a food web. All the rats are removed by a disease. Which organism will be most affected?

Food web: grass is eaten by grasshopper and rat; grasshopper is eaten by frog; frog is eaten by snake; rat is eaten by snake and owl — Diagram 1

Frog
Grasshopper
Owl
Grass

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The owl eats only rats in this web, so it loses its only food source. The snake can still eat frogs. Grass would increase, and the grasshopper and frog are not directly affected.

For the teacher: Analysing, high difficulty, standard 2.3.5

Textbook p. 38

Question 12

An oil palm plantation has too many rats. Which method is best for a sustainable plantation?

Keep owls in the plantation
Spray strong pesticides every week
Burn the area around the plantation
Use poison and throw away the dead rats in the river

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Owls are natural predators of rats, so this is biological control that avoids pollution. Pesticides, burning and poison pollute air, soil and water.

For the teacher: Evaluating, high difficulty, standard 2.4.1

Textbook p. 40

Section B: structured questions

32 marks

Answer all questions. Write your answers in the spaces provided.

Question 13

A food chain in a forest is: Grass → Grasshopper → Frog → Snake. State the role of each organism.

[1 mark] (a)Grass

AProducerBPrimary consumerCSecondary consumerDTertiary consumer

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Producer

[1 mark] (b)Grasshopper

AProducerBPrimary consumerCSecondary consumerDTertiary consumer

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Primary consumer

[1 mark] (c)Frog

AProducerBPrimary consumerCSecondary consumerDTertiary consumer

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Secondary consumer

[1 mark] (d)Snake

AProducerBPrimary consumerCSecondary consumerDTertiary consumer

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Tertiary consumer

For the teacher: Remembering, low difficulty, standard 2.1.1

Textbook p. 23

Question 14

Diagram 2 shows a food web in a grass field.

[1 mark] (a)Write the longest food chain in the web.

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Grass → Grasshopper → Frog → Snake1

Tick each point you got.

[1 mark] (b)Why is grass a producer?

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It makes its own food by photosynthesis1

Tick each point you got.

[2 marks] (c)Predict what will happen to the number of grasshoppers if all the frogs die. Give a reason.

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The number of grasshoppers increases1
Frogs eat grasshoppers, so there are fewer predators and fewer grasshoppers are eaten1

Tick each point you got.

For the teacher: Analysing, medium difficulty, standard 2.1.2

Textbook p. 24

Question 15

State the type of interaction in each situation.

[1 mark] (a)A tapeworm lives in the intestine of a human and absorbs digested food.

AMutualismBCommensalismCParasitismDCompetition

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Parasitism

[1 mark] (b)The fungi in a lichen supply water and minerals to the algae, and the algae supply food to the fungi.

AMutualismBCommensalismCParasitismDCompetition

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Mutualism

[1 mark] (c)Two plants in a forest grow close together and fight for sunlight and space.

AMutualismBCommensalismCParasitismDCompetition

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Competition

[1 mark] (d)A bird's nest fern grows on the branch of a tree to get sunlight. The tree is not harmed.

AMutualismBCommensalismCParasitismDCompetition

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Commensalism

For the teacher: Applying, low difficulty, standard 2.3.3

Textbook p. 33

Question 16

A pupil put 10 woodlice on a wire gauze over a Petri dish with two partitions. Partition P had hot water (50 °C) and partition Q had room-temperature water (26 °C to 30 °C). After five minutes the number of woodlice above each partition was counted. Diagram 3 shows the results.

Bar chart: hot water partition P, 1 woodlouse; room-temperature partition Q, 9 woodlice — Diagram 3

[1 mark] (a)State the manipulated variable.

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Temperature (of the water in the partition)1

Tick each point you got.

[1 mark] (b)State the responding variable.

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Distribution (number) of woodlice in each partition1

Tick each point you got.

[1 mark] (c)State a conclusion for this experiment.

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Any 1 points

Woodlice prefer a place with a medium (room) temperature to a hot place1
The hypothesis is accepted1

Tick each point you got.

[1 mark] (d)State one variable that must be kept constant.

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Any 1 points

Number of woodlice1
Light1
Humidity1

Tick each point you got.

For the teacher: Analysing, medium difficulty, standard 2.3.1

Textbook p. 30

Question 17

A farmer kept owls to catch rats on his farm. He then removed all the owls. Diagram 4 shows the number of rats on the farm after the owls were removed.

Line graph: number of rats against month after the owls were removed; 100 at month 0 and 2, 160 at month 4, 300 at month 6, 520 at month 8, 800 at month 10, 1100 at month 12 — Diagram 4

[1 mark] (a)How many rats are there at month 6?

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3001

Tick each point you got.

[1 mark] (b)By how many did the rat population increase from month 0 to month 12?

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1100 − 100 = 10001

Tick each point you got.

[2 marks] (c)Explain why the number of rats increased.

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The owls (predators) were removed1
So fewer rats were eaten and more rats survived and reproduced1

Tick each point you got.

[1 mark] (d)Suggest one effect of the large rat population on the farm.

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Any 1 points

Rats eat the crops / stored grain, so the harvest is reduced1
Rats spread disease1

Tick each point you got.

For the teacher: Analysing, high difficulty, standard 2.3.4

Textbook p. 37

Question 18

Burning of fossil fuels and unrestricted logging affect the carbon cycle and the oxygen cycle.

[2 marks] (a)State two processes in which living things release carbon dioxide.

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Respiration (by plants and animals)1
Decay / decomposition by bacteria and fungi1

Tick each point you got.

[2 marks] (b)Explain how unrestricted logging upsets the balance of oxygen and carbon dioxide in the air.

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Fewer trees carry out photosynthesis1
Less carbon dioxide is absorbed and less oxygen is released, so carbon dioxide increases1

Tick each point you got.

[1 mark] (c)Suggest one step to solve the problem caused by burning fossil fuels.

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Any 1 points

Use public transport1
Replant trees1
Tighten laws1

Tick each point you got.

For the teacher: Understanding, medium difficulty, standard 2.2.1

Textbook p. 26

Question 19

Hana and Mei have different opinions about decomposers. Hana: "Producers can live without decomposers because they make their own food." Mei: "Without decomposers, producers will not get enough nutrients and may die."

[1 mark] (a)Whose opinion is correct?

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Mei1

Tick each point you got.

[2 marks] (b)Justify your answer.

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Producers make food by photosynthesis but still need minerals / nutrients from the soil1
Decomposers break down dead organisms and release these nutrients back to the soil, so without them the nutrients run out1

Tick each point you got.

For the teacher: Evaluating, high difficulty, standard 2.1.1

Textbook p. 43

Question 20

A town council plans to plant a city forest, which is an area with many trees, in the middle of the city.

[2 marks] (a)State two benefits of the city forest in maintaining a balanced ecosystem.

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Any 2 points

Trees absorb carbon dioxide and release oxygen (photosynthesis), keeping the air balanced1
Provides a habitat and food for animals1
Roots hold the soil and reduce soil erosion and flash floods1
Releases water vapour by transpiration1

Tick each point you got.

[1 mark] (b)Suggest one way the council can make sure the forest is not destroyed.

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Any 1 points

Enforce laws / carry out patrols1
Increase public awareness through campaigns1

Tick each point you got.

For the teacher: Creating, high difficulty, standard 2.4.1

Textbook p. 43

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