The Interdependence of Life

23 Grade 9 Integrated Science questions on The Interdependence of Life, with worked marking schemes. 23 questions are available on this topic in full.

1. Question 1

   4 marks

   Study the food chain below and answer the questions that follow. Grass -> Grasshopper -> Frog -> Snake

   (a) Identify the producer and the secondary consumer in this food chain. (2 marks)

   (b) Explain what would happen to the population of grasshoppers if all the frogs were removed from this habitat. (2 marks)

   (4 marks)

   Marking scheme

   (a) Producer: grass; Secondary consumer: frog (it feeds on the grasshopper, which is the primary consumer). (b) The population of grasshoppers would increase, because the frogs that feed on (prey on) them have been removed, so fewer grasshoppers are eaten and more survive and reproduce. (The increase may later be limited as the grass they feed on is reduced.)

2. Question 2

   1 mark

   In an ecosystem, animals that hunt, kill and feed on other animals are called:

   A. Scavengers

   B. Producers

   C. Predators

   D. Prey

   (1 mark)

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3. Question 3

   1 mark

   A food chain shows

   A. the water cycle

   B. how animals reproduce

   C. the structure of cells

   D. the flow of energy from one organism to another

   (1 mark)

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4. Question 4

   1 mark

   Which group of organisms breaks down dead plants and animals, returning nutrients to the soil?

   A. Decomposers

   B. Carnivores

   C. Herbivores

   D. Producers

   (1 mark)

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5. Question 5

   1 mark

   A relationship in which the oxpecker bird feeds on ticks found on the skin of a buffalo, benefiting both organisms, is an example of:

   A. Predation

   B. Mutualism (symbiosis)

   C. Parasitism

   D. Competition

   (1 mark)

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6. Question 6

   1 mark

   In a food chain found in the Maasai Mara: grass → zebra → lion. What is the role of the grass in this food chain?

   A. Producer

   B. Secondary consumer

   C. Decomposer

   D. Primary consumer

   (1 mark)

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7. Question 7

   4 marks

   Study the food chain below: Grass -> Grasshopper -> Lizard -> Hawk

   (a) Name the producer in the food chain. (1 mark)

   (b) State the trophic level occupied by the lizard. (1 mark)

   (c) Explain what would happen to the population of grasshoppers if all the lizards were removed from this habitat. (2 marks)

   (4 marks)

   Marking scheme

   (a) The producer is grass. (b) The lizard is a secondary consumer (it occupies the third trophic level). (c) If all the lizards were removed, the population of grasshoppers would increase (in the short term) because their predator has been removed, so fewer grasshoppers are eaten. As a result the grass (their food) would be eaten more heavily and may reduce, which could later cause the grasshopper population to fall again due to shortage of food.

8. Question 8

   5 marks

   A grassland food chain was drawn as: grass → grasshopper → lizard → hawk.

   (a) Identify the producer and the primary consumer in this food chain. (2 marks)

   (b) Explain what would happen to the population of grasshoppers if all the lizards were removed from the grassland. (3 marks)

   (5 marks)

   Marking scheme

   (a) Producer = grass (it makes its own food by photosynthesis). Primary consumer = grasshopper (it feeds directly on the producer). (2 marks) (b) If all the lizards were removed, the grasshoppers would have no predator feeding on them, so their population would increase rapidly at first. As a result, the grasshoppers would eat more grass, and the grass (producer) population would fall. Eventually, the shortage of grass (food) would reduce the grasshopper population again. (Any two clear linked points = increase then later decline due to food shortage) (3 marks)

9. Question 9

   2 marks

   Distinguish between a food chain and a food web.

   (2 marks)

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10. Question 10

    3 marks

    A farmer sprayed a strong pesticide that killed all the decomposers in the soil of his farm.

    (a) State one role of decomposers in the ecosystem.

    (b) Explain one long-term effect the loss of decomposers would have on the fertility of the soil.

    (3 marks)

    Marking scheme

    (a) Decomposers break down dead plant and animal matter / recycle nutrients back into the soil (1 mark). (b) Without decomposers, dead matter would accumulate and nutrients would not be released/recycled back into the soil (1 mark), so the soil would become less fertile and plants would grow poorly (1 mark).

11. Question 11

    4 marks

    Using a named example, explain what is meant by mutualism (symbiosis) and how each organism benefits.

    (4 marks)

    Marking scheme

    Mutualism is an association between two organisms of different species in which both benefit (1 mark). Named example, e.g. oxpecker and buffalo / rhizobium bacteria and legume roots (1 mark). Benefit to first organism explained, e.g. oxpecker gets food (ticks) (1 mark). Benefit to second organism explained, e.g. buffalo is freed of parasites/ticks (1 mark). Accept any valid named example correctly explained.

12. Question 12

    4 marks

    Study the food chain below and answer the questions that follow: maize → weaver bird → snake → hawk.

    (a) Name the producer.

    (b) Name the primary consumer.

    (c) State what would happen to the population of weaver birds if all the snakes were killed.

    (4 marks)

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13. Question 13

    1 mark

    Decomposers are important in an ecosystem because they

    A. break down dead organisms and return nutrients to the soil

    B. produce food from sunlight

    C. produce oxygen

    D. eat only living organisms

    (1 mark)

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14. Question 14

    3 marks

    Study the food chain below and answer the questions that follow:

    Grass → Zebra → Lion → Decomposer

    (a) Identify the producer.

    (b) Name the primary consumer.

    (c) What would happen to the lion population if all zebras died?

    (3 marks)

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15. Question 15

    1 mark

    The original source of energy for almost all food chains on Earth is:

    A. The Sun

    B. Decomposers

    C. Water

    D. The soil

    (1 mark)

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16. Question 16

    1 mark

    If all the frogs in a food chain were removed, the population of grasshoppers would likely

    A. decrease

    B. increase

    C. remain the same

    D. disappear

    (1 mark)

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17. Question 17

    1 mark

    In a food chain, the organism that makes its own food is called a

    A. producer

    B. decomposer

    C. predator

    D. consumer

    (1 mark)

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18. Question 18

    4 marks

    The following is a simple food chain in a grassland: Grass → Grasshopper → Lizard → Hawk

    (a) Name the organism that is the producer in this food chain. (1 mark)

    (b) State the trophic level occupied by the lizard. (1 mark)

    (c) Explain what would happen to the population of grasshoppers if all the lizards were removed from this ecosystem. (2 marks)

    (4 marks)

    Marking scheme

    (a) Grass (it is green and makes its own food by photosynthesis). (b) The lizard is a secondary consumer (it occupies the third trophic level). (c) The grasshopper population would increase at first because their predator (the lizard) has been removed, so fewer grasshoppers are eaten; eventually the increased number of grasshoppers may eat up much of the grass, leading to food shortage that then reduces their numbers.

19. Question 19

    1 mark

    In the food chain grass → grasshopper → lizard → hawk, the lizard is best described as a:

    A. Primary consumer

    B. Decomposer

    C. Producer

    D. Secondary consumer

    (1 mark)

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20. Question 20

    4 marks

    Explain the importance of conservation in maintaining the balance in an ecosystem.

    (4 marks)

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21. Question 21

    1 mark

    A food web is different from a food chain because a food web

    A. shows interconnected food chains in an ecosystem

    B. is simpler than a food chain

    C. has only one producer

    D. does not include decomposers

    (1 mark)

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22. Question 22

    1 mark

    In the food chain: Grass → Grasshopper → Frog → Snake → Hawk, the secondary consumer is the

    A. Snake

    B. Frog

    C. Grasshopper

    D. Hawk

    (1 mark)

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23. Question 23

    1 mark

    A tapeworm living in the intestines of a human, feeding on digested food and harming the human, illustrates:

    A. Competition

    B. Mutualism

    C. Commensalism

    D. Parasitism

    (1 mark)

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