krit.club logo

Ecology and Earth Science - Human Impact on the Environment

Grade 7IB

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

🔑Concepts

•

The Greenhouse Effect: Natural process where gases like CO2CO_2, CH4CH_4 (methane), and N2ON_2O (nitrous oxide) trap heat in the atmosphere. Human activities like burning fossil fuels increase these concentrations, leading to Global Warming.

•

Ocean Acidification: Excess CO2CO_2 from the atmosphere dissolves in seawater to form carbonic acid (H2CO3H_2CO_3), which lowers the pHpH of the oceans and harms marine life such as coral reefs.

•

Eutrophication: Nutrient runoff (specifically nitrates NO3−NO_3^- and phosphates PO43−PO_4^{3-}) into water bodies causes algal blooms, leading to oxygen depletion (O2O_2 reduction) and the death of aquatic organisms.

•

Acid Rain: Emissions of sulfur dioxide (SO2SO_2) and nitrogen oxides (NOxNO_x) react with water vapor in the atmosphere to produce acidic compounds like sulfuric acid (H2SO4H_2SO_4) and nitric acid (HNO3HNO_3).

•

Deforestation and the Carbon Cycle: Trees act as carbon sinks. Removing them reduces the rate of photosynthesis, represented by 6CO2+6H2O→C6H12O6+6O26CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2, leaving more CO2CO_2 in the atmosphere.

•

Bioaccumulation and Biomagnification: The increase in concentration of toxins (like mercury or DDTDDT) as they move up the food chain, where top predators have the highest concentration.

📐Formulae

6CO2+6H2O→lightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6 + 6O_2

CO2+H2O→H2CO3CO_2 + H_2O \rightarrow H_2CO_3

SO2+H2O→H2SO3SO_2 + H_2O \rightarrow H_2SO_3

pH=−log⁡[H+]pH = -\log[H^+]

💡Examples

Problem 1:

Explain the chemical process that occurs when CO2CO_2 is absorbed by the ocean and how it affects the pHpH.

Solution:

CO2+H2O→H2CO3→H++HCO3−CO_2 + H_2O \rightarrow H_2CO_3 \rightarrow H^+ + HCO_3^-

Explanation:

When carbon dioxide dissolves in water, it forms carbonic acid (H2CO3H_2CO_3). This acid dissociates to release hydrogen ions (H+H^+). An increase in H+H^+ ions results in a lower pHpH value, making the water more acidic, which dissolves the calcium carbonate (CaCO3CaCO_3) shells of marine organisms.

Problem 2:

If a pesticide has a concentration of 0.000003 ppm0.000003\text{ ppm} in water and it increases by a factor of 1010 at every level of a 4-step food chain, what is the concentration in the apex predator?

Solution:

0.000003×104=0.03 ppm0.000003 \times 10^4 = 0.03\text{ ppm}

Explanation:

This demonstrates biomagnification. At each trophic level, the toxin becomes more concentrated because the consumer eats many organisms from the level below. Starting at 3×10−63 \times 10^{-6}, after four transfers (10×10×10×1010 \times 10 \times 10 \times 10), the concentration reaches 0.03 ppm0.03\text{ ppm}.

Problem 3:

How does burning coal (S+O2→SO2S + O_2 \rightarrow SO_2) contribute to the degradation of marble statues (CaCO3CaCO_3)?

Solution:

H2SO4+CaCO3→CaSO4+H2O+CO2H_2SO_4 + CaCO_3 \rightarrow CaSO_4 + H_2O + CO_2

Explanation:

Burning coal releases SO2SO_2, which forms sulfuric acid (H2SO4H_2SO_4) in rain. When this acid rain hits marble (CaCO3CaCO_3), a chemical reaction occurs that converts the solid stone into soluble gypsum (CaSO4CaSO_4), water, and CO2CO_2 gas, causing the statue to erode.