SPM Biology 2014


8 . (a) Diagram 8.1 shows a food chain in a paddy field. Explain the importance of each organism in the food chain to maintain ecosystem balance.

Rajah 8.1 menunjukkan satu rantai makanan di sawah padi. Terangkan kepentingan setiap organisma di dalam rantai makanan itu untuk mengekalkan keseimbangan ekosistem.


(b) Diagram 8.2 shows two types of human activities in an ecosystem. Explain the impact of each activity on the ecosystem.

Rajah 8.2 menunjukkan dua jenis aktivit manusia dalam suatu ekosistem. Terangkan impak setiap aktiviti kepada ekosistem tersebut.

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    8. a)Paddy plants (producers) are autotrophs. They can manufacture organic substances from water and CO2 with the presence sunlight. Thus, they produce their own food via photosynthesis. This food is then consumed by the primary consumers (caterpillars).

    -Indirectly the producers are producing food for all organisms in the food chain.

    -Consumers cannot synthesize their own food, thus they must consume other organisms in order to obtain nutrients and energy.

    -Primary consumers like the caterpillars consume plants (producers) so they’re herbivores.

    -Secondary consumers are usually carnivores or omnivores (bird). They consume primary consumers in other to obtain energy and nutrients.

    -Tertiary consumers (eagle) consist mainly of carnivores. They’re usually predators which prey on secondary consumers.

    -All organisms must be present in the food chain for the balance of the ecosystem.

    -Furthermore, going up the trophic levels the number of organisms decrease as their size increases. If there are too many tertiary consumers compared to the secondary consumers, the food chain suffers and the ecosystem becomes unbalanced.

    -Similar between the secondary and primary consumers, and the producers with the primary consumers.


    b)-Excess use of fertilizer causes eutrophication to occur.

    -Fertilizer contains phosphates and nitrates. When soil from farm land is leached into the pond, the excess nutrients causes the growth of algae.

    -There might be algal bloom which creates a blanket of algae covering the surface of the pond. Sunlight would not be able to penetrate into the water, thus aquatic plants cannot photosynthesize and start to die off, causing less oxygen to be produced.

    -Accumulation of organic material attracts decomposing aerobic microorganisms which grow rapidly causing the levels of oxygen to decrease even further.

    -This reduction in the concentration of oxygen causes an increase in biochemical oxygen demand (B.O.D).

    -Resulting in the death of more aquatic organisms like fish.


    -Deforestation with excessive tree logging causes the concentration of atmospheric carbon dioxide (CO2) to increase as CO2 is not effectively removed from the atmosphere by photosynthesis. 

    -This causes the greenhouse effect to occur as greenhouse gases such as CO2 start to accumulate.

    -The greenhouse effect traps heat within the atmosphere, this increases the Earth’s and atmosphere’s average temperature, causing global warming to occur.

    -Furthermore, landslides may occur due to soil erosion as there aren’t any roots to hold down soil.

    -There is also risk in losing Earth’s carbon sinks and water catchment areas.

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