SolveItClass 9 · NCERT

NCERT Solutions · Class 9 Science Earth as a System: Energy, Matter, and Life

23 questions · 23 still being checked

Pause and Ponder 13.5–13.6 (part 8 of 11)

  1. Exercise 13.5

    What would happen to plants and animals on Earth if the biogeochemical cycles were disrupted and stopped? Explain by giving a few examples. Burning of fossil fuels and deforestation saturate natural carbon sinks The overuse of fertilisers in agriculture adds excessive

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    NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.

    Life would collapse, because the biogeochemical cycles are what keep returning nutrients to living organisms; if they stopped, each nutrient would be locked in a form no organism could use.
    NCERT_Solution_Class9_Science_Ch13_PP_Q13-5
    Carbon cycle stops — respiration, decomposition and combustion no longer return \(\displaystyle CO_{2} \) to the air, so plants run out of raw material for photosynthesis and no food is made for any organism.
    Oxygen cycle stops — the \(\displaystyle O_{2} \) used up by respiration and combustion is not restored by photosynthesis, so plants and animals eventually suffocate.
    Nitrogen cycle stops — atmospheric \(\displaystyle N_{2} \) is non-reactive and cannot be used directly; with no ammonia or nitrate in the soil, plants cannot build proteins and nucleic acids, and animals that eat them are starved of nitrogen too.
    Water cycle stops — no evaporation, no clouds, no precipitation; rivers, lakes and groundwater are never refilled, and terrestrial life dries out.
    Dead bodies and waste would pile up undecomposed, permanently trapping the nutrients they contain instead of returning them to the soil.

  2. Exercise 13.6

    Discuss how human activities increase the concentration of greenhouse gases in the atmosphere. What would you do as an individual to reduce the emission of greenhouse gas? 266\displaystyle 266 Exploration|Grade 9\displaystyle 9

    Not cross-checked

    NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.

    Human activities raise greenhouse gases chiefly by burning fossil fuels and clearing forests.
    NCERT_Solution_Class9_Science_Ch13_PP_Q13-6
    Burning coal, oil and gas for electricity, heating, cooking, transport and industry releases carbon that took millions of years to bury, returning it as \(\displaystyle CO_{2} \) on a very short time scale.
    Deforestation removes the trees that absorb \(\displaystyle CO_{2} \), and saturates natural carbon sinks like forests and oceans, so more \(\displaystyle CO_{2} \) stays in the air.
    Vehicular emissions add pollutants that react with sunlight to form ground-level smog and ozone.
    Overuse of nitrogen fertilisers, and the energy-intensive Haber–Bosch process behind them (about \(\displaystyle 1-2\% \) of global energy), add further emissions.
    Result: atmospheric \(\displaystyle CO_{2} \) has risen by about \(\displaystyle 35\% \) since $\displaystyle 1960$, from \(\displaystyle 315 \) ppm to \(\displaystyle 420 \) ppm.
    As an individual I would: walk, cycle or use public transport instead of a private vehicle; switch off lights, fans and appliances when not in use and prefer LED lamps; support solar and other renewable energy at home; plant trees and look after them; save water and avoid wasting food; and reduce, reuse and recycle materials — the mindful lifestyle promoted by Mission LiFE.