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Ecology - Human Impact on the Biosphere

Grade 9IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Greenhouse Effect: Increased concentrations of greenhouse gases like CO2CO_2, CH4CH_4, and N2ON_2O trap infrared radiation in the atmosphere, leading to an increase in the Earth's mean surface temperature.

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Eutrophication: The runoff of fertilizers containing high levels of Nitrates (NO3−NO_3^-) and Phosphates (PO43−PO_4^{3-}) into water bodies causes algal blooms, which deplete dissolved oxygen (O2O_2) and lead to the death of aquatic organisms.

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Bioaccumulation and Biomagnification: Persistent organic pollutants like DDTDDT or heavy metals like Mercury (HgHg) accumulate in the tissues of individual organisms and increase in concentration at higher trophic levels in a food chain.

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Ozone Layer Depletion: The release of Chlorofluorocarbons (CFCsCFCs) causes the breakdown of Stratospheric Ozone (O3O_3), which increases the amount of harmful UVUV radiation reaching the Earth's surface.

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Deforestation: The large-scale removal of trees reduces the rate of carbon sequestration via photosynthesis (6CO2+6H2O→C6H12O6+6O26CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2), leading to higher atmospheric CO2CO_2 levels and habitat loss.

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Acid Rain: The combustion of fossil fuels releases SO2SO_2 and NOxNO_x, which react with water vapor to form Sulfuric acid (H2SO4H_2SO_4) and Nitric acid (HNO3HNO_3), lowering the pHpH of precipitation.

📐Formulae

Efficiency of Energy Transfer=(Energy available after transferEnergy available before transfer)×100\text{Efficiency of Energy Transfer} = \left( \frac{\text{Energy available after transfer}}{\text{Energy available before transfer}} \right) \times 100

Net Primary Productivity (NPP)=Gross Primary Productivity (GPP)−Respiration (R)\text{Net Primary Productivity (NPP)} = \text{Gross Primary Productivity (GPP)} - \text{Respiration (R)}

Population Growth Rate=(Births+Immigration)−(Deaths+Emigration)Total Population×100\text{Population Growth Rate} = \frac{(\text{Births} + \text{Immigration}) - (\text{Deaths} + \text{Emigration})}{\text{Total Population}} \times 100

6CO2+6H2O+light energy→C6H12O6+6O26CO_2 + 6H_2O + \text{light energy} \rightarrow C_6H_{12}O_6 + 6O_2

💡Examples

Problem 1:

In a specific aquatic ecosystem, the concentration of a pesticide in the water is 0.000003 ppm0.000003\text{ ppm}. If the concentration magnifies by a factor of 1010 at each subsequent trophic level, calculate the concentration in a tertiary consumer (the 4th trophic level).

Solution:

Concentration =0.000003×10×10×10=0.003 ppm= 0.000003 \times 10 \times 10 \times 10 = 0.003\text{ ppm}

Explanation:

This demonstrates biomagnification. The pesticide concentration increases as it moves from producers (T1T_1) to primary consumers (T2T_2), secondary consumers (T3T_3), and finally tertiary consumers (T4T_4).

Problem 2:

A lake experiences a sudden influx of PO43−PO_4^{3-} from agricultural runoff. Explain the chemical impact on the Biochemical Oxygen Demand (BODBOD).

Solution:

The BODBOD will increase significantly.

Explanation:

The phosphates act as a limiting nutrient, causing an algal bloom. When the algae die, aerobic bacteria decompose them, consuming large amounts of dissolved O2O_2. This increase in microbial respiration is measured as an increase in BODBOD, often leading to hypoxia (<2 mg/L< 2\text{ mg/L} of O2O_2).

Human Impact on the Biosphere - Revision Notes & Key Formulas | IB Grade 9 Science