Biology questions, chapter 9

Nama / NameKelas / ClassTarikh / Date

Ecosystem

46 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 describes a population?

All the organisms of different species in a habitat
Organisms of one species living in the same habitat
A group of similar organisms able to interbreed
The natural living place of an organism

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A population is organisms of the same species in one habitat. Option A is a community, C is a species and D is a habitat.

For the teacher: Remembering, low difficulty, standard 9.1.1

Textbook p. 171

Question 2

What is the niche of an organism?

The place where it lives
The number of its species in an area
Its role in the ecosystem
The food that it eats

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A niche is the role of an organism in an ecosystem, covering its behaviour and interactions. Where it lives is its habitat.

For the teacher: Remembering, low difficulty, standard 9.1.1

Textbook p. 171

Question 3

Nitrobacter sp. makes organic compounds without light, using energy from oxidising inorganic substances. How is it classified?

Chemoautotroph
Photoautotroph
Saprotroph
Parasite

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It gains energy by oxidising inorganic substances (chemosynthesis), so it is a chemoautotroph.

For the teacher: Understanding, low difficulty, standard 9.1.3

Textbook p. 176

Question 4

What is the role of decomposers in an ecosystem?

To trap energy from the sun
To feed on producers
To hunt primary consumers
To break down dead matter and waste

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Decomposers such as bacteria and fungi break dead organisms and waste into simple substances like carbon dioxide and ammonia.

For the teacher: Understanding, low difficulty, standard 9.1.4

Textbook p. 177

Question 5

A grassland food chain starts with producers containing 5 000 kJ. About how much energy reaches the secondary consumers?

500 kJ
50 kJ
5 kJ
5 000 kJ

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Only 10% passes on at each level: 5 000 × 0.1 = 500 kJ (primary), then 500 × 0.1 = 50 kJ (secondary).

For the teacher: Applying, medium difficulty, standard 9.1.6

Textbook p. 181

Question 6

A remora fish feeds on scraps from a shark. The shark is neither helped nor harmed. What interaction is this?

Mutualism
Parasitism
Commensalism
Predation

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One organism benefits and the other is unaffected: commensalism.

For the teacher: Understanding, low difficulty, standard 9.1.7

Textbook p. 182

Question 7

What is the function of the pneumatophore roots of Avicennia sp.?

Gas exchange in waterlogged soil
Support against strong waves
Storage of salt
Germination of seeds on the parent plant

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Pneumatophores project above the mud and exchange gases through lenticels. Prop roots give support and viviparous seeds germinate on the parent.

For the teacher: Understanding, low difficulty, standard 9.1.8

Textbook p. 187

Question 8

Which plants are the pioneer species in the coastal zone of a mangrove forest?

Bruguiera sp.
Rhizophora sp.
Nypa fruticans
Avicennia sp. and Sonneratia sp.

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Avicennia and Sonneratia colonise the coastal zone first and trap mud; Rhizophora then succeeds them.

For the teacher: Remembering, low difficulty, standard 9.1.8

Textbook p. 188

Question 9

A species is found in 6 out of 8 quadrats. What is its frequency?

6%
48%
75%
133%

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Frequency = 6 ÷ 8 × 100% = 75%.

For the teacher: Applying, low difficulty, standard 9.2.2

Textbook p. 193

Question 10

25 beetles are marked and released. A later sample of 40 beetles contains 5 marked ones. What is the estimated population?

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Population = (25 × 40) ÷ 5 = 200.

For the teacher: Applying, high difficulty, standard 9.2.2

Textbook p. 195

Question 11

What usually causes a clumped pattern of population distribution?

Strong competition among individuals
Little interaction among individuals
A constant temperature
Uneven spread of resources

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Clumped groups form where resources are patchy. Uniform distribution results from competition; random from little interaction.

For the teacher: Understanding, low difficulty, standard 9.2.1

Textbook p. 191

Question 12

Diagram 1 shows a food web. All the frogs die from a disease. What is the most likely immediate effect?

Food web: grass to grasshopper and rabbit; grasshopper to frog; frog to snake; rabbit to fox and eagle. Arrows point to the consumer. — Diagram 1

The number of grasshoppers decreases
The number of grasshoppers increases and the snake population decreases
The number of rabbits decreases
The number of foxes increases

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Frogs eat grasshoppers, so grasshoppers increase. The snake feeds only on frogs in this web, so it decreases.

For the teacher: Analysing, medium difficulty, standard 9.1.5

Textbook p. 179

Section B: structured questions

34 marks

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

Question 13

Diagram 2 shows a food web in a grassland.

Food web: grass to grasshopper and rabbit; grasshopper to frog; frog to snake; rabbit to fox and eagle. — Diagram 2

[1 mark] (a)How many food chains are in the food web?

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Tick each point you got.

[1 mark] (b)State the trophic level of the snake in the longest food chain.

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Fourth trophic level1

Grass, grasshopper, frog, snake: the snake is a tertiary consumer.

Tick each point you got.

[1 mark] (c)Name one organism that is a secondary consumer.

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Frog / fox / eagle (in the rabbit chain)1

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[2 marks] (d)All the rabbits are removed. Explain the effect on the fox.

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The fox has no food in this web [1]1
so its population decreases / the fox dies or migrates [1]1

Tick each point you got.

For the teacher: Analysing, low difficulty, standard 9.1.5

Textbook p. 179

Question 14

Give the meaning of each term.

[1 mark] (a)Habitat

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The natural surrounding or living place of an organism1

Tick each point you got.

[1 mark] (b)Community

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Populations of all organisms of different species living in the same habitat and interacting with each other1

Tick each point you got.

[1 mark] (c)Niche

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The role of an organism in an ecosystem, including its behaviour and interactions with biotic and abiotic components1

Tick each point you got.

For the teacher: Remembering, low difficulty, standard 9.1.1

Textbook p. 171

Question 15

Name the type of interaction in each situation.

[1 mark] (a)A tapeworm absorbs nutrients from the human intestine.

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Parasitism1

Tick each point you got.

[1 mark] (b)Two different plant species compete for sunlight.

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Interspecific competition1

Tick each point you got.

[1 mark] (c)A myna eats lice from a buffalo.

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Mutualism1

The myna gets food and the buffalo is rid of lice, so both benefit.

Tick each point you got.

For the teacher: Understanding, low difficulty, standard 9.1.7

Textbook p. 183

Question 16

A food chain is: paddy, grasshopper, frog, snake. The paddy contains 8 000 kJ of energy.

[1 mark] (a)Calculate the energy transferred to the frog.

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8 000 × 0.1 × 0.1 = 80 kJ1

Grasshopper 800 kJ, frog 80 kJ.

Tick each point you got.

[1 mark] (b)Calculate the energy transferred to the snake.

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8 kJ1

Tick each point you got.

[2 marks] (c)Explain why food chains usually end at the secondary or tertiary consumer.

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Only about 10% of energy is passed to the next level [1]1
the rest is lost as heat, in life processes and excretion, so too little remains for higher levels [1]1

Tick each point you got.

For the teacher: Applying, medium difficulty, standard 9.1.6

Textbook p. 181

Question 17

Mangrove trees grow in soft, muddy soil that is covered by seawater at high tide.

[2 marks] (a)Name the roots of Rhizophora sp. and state their function.

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Prop roots [1]1
support the tree against strong wind and waves [1]1

Tick each point you got.

[2 marks] (b)Explain how pneumatophore roots help the tree survive in waterlogged mud.

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They project above the mud / water surface [1]1
gas exchange takes place through lenticels because the mud lacks oxygen [1]1

Tick each point you got.

[1 mark] (c)What is the advantage of viviparous seeds to mangrove trees?

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Seedlings fall and stick into the mud so they are not uprooted by waves1

Tick each point you got.

For the teacher: Understanding, low difficulty, standard 9.1.8

Textbook p. 187

Question 18

A mangrove area has Avicennia sp. near the sea, Rhizophora sp. in the middle and Bruguiera sp. inland.

[1 mark] (a)Name the process in which Rhizophora sp. gradually replaces Avicennia sp.

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Succession1

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[2 marks] (b)Explain how Avicennia sp. prepares the area for Rhizophora sp.

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Its roots trap mud and organic substances [1]1
the soil becomes higher and denser, which suits Rhizophora [1]1

Tick each point you got.

[2 marks] (c)The Rhizophora zone is cleared to build a fish pond. Give two effects on the ecosystem.

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Any 2 points

Fewer producers, so the food web is disrupted [1]1
loss of shelter for fish and crabs / less protection from waves and erosion [1]1
loss of habitat so biodiversity decreases [1]1

Tick each point you got.

For the teacher: Evaluating, high difficulty, standard 9.1.8

Textbook p. 188

Question 19

A student used ten 1 m × 1 m quadrats to study plant X. The numbers of plants in the quadrats were 3, 0, 5, 2, 0, 4, 1, 0, 3, 2. Plant X covered a total area of 1.2 m² in all the quadrats.

[1 mark] (a)Calculate the frequency of plant X.

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7 ÷ 10 × 100 = 70%1

Tick each point you got.

[1 mark] (b)Calculate the density of plant X.

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20 ÷ (10 × 1) = 2 plants per m²1

Tick each point you got.

[1 mark] (c)Calculate the coverage percentage.

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1.2 ÷ (10 × 1) × 100 = 12%1

Tick each point you got.

[1 mark] (d)Why must the quadrats be placed randomly?

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To avoid bias so the sample represents the whole area1

Tick each point you got.

For the teacher: Applying, medium difficulty, standard 9.2.2

Textbook p. 193

Question 20

To estimate the number of fish in a pond, 60 fish were caught, marked and released. A week later, 45 fish were caught and 9 of them were marked.

[2 marks] (a)Calculate the estimated population size.

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(60 × 45) ÷ 9 [1]1
= 300 fish [1]1

Tick each point you got.

[1 mark] (b)Suggest a suitable marker.

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Non-toxic paint / Indian ink / a small tag that does not harm or attract predators1

Tick each point you got.

[2 marks] (c)State two assumptions that make the estimate reliable.

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Marked fish mix evenly with the population [1]1
no fish are born, die, enter or leave during the week / marks do not wear off [1]1

Tick each point you got.

For the teacher: Evaluating, medium difficulty, standard 9.2.2

Textbook p. 195

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