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Biology - Ecology and Environmental Systems (Energy Flow and Human Impact)

Grade 10IB

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

🔑Concepts

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Energy enters most ecosystems as sunlight and is converted into chemical energy by producers (autotrophsautotrophs) via photosynthesis: 6CO2+6H2O→lightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6O_2.

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Trophic Levels: Energy flows through food chains from primary producers to primary consumers, secondary consumers, and tertiary consumers.

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The 10%10\% Rule: Approximately only 10%10\% of the energy available at one trophic level is passed to the next; the rest is lost as heat during cellular respiration, through excretion, or remains in unconsumed parts.

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Pyramids of Energy: These diagrams represent the flow of energy through trophic levels and are always upright, measured in units of energy per area per time (e.g., kJ m−2 yr−1kJ \, m^{-2} \, yr^{-1}).

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Bioaccumulation: The gradual accumulation of substances, such as pesticides (e.g., DDTDDT) or heavy metals (e.g., Hg2+Hg^{2+}), in an individual organism over time.

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Biomagnification: The increase in concentration of a pollutant as it moves up the food chain, reaching toxic levels in top predators.

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Eutrophication: The process where nutrient enrichment (usually nitrates NO3−NO_3^- and phosphates PO43−PO_4^{3-}) leads to excessive algal growth, oxygen depletion (BODBOD increase), and death of aquatic life.

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Greenhouse Effect: Gases like CO2CO_2, CH4CH_4, and N2ON_2O trap long-wave infrared radiation in the atmosphere, maintaining Earth's temperature but leading to global warming when concentrations increase due to human activity.

📐Formulae

NPP=GPP−RNPP = GPP - R

Trophic Efficiency=(Energy at Level n+1Energy at Level n)×100%\text{Trophic Efficiency} = \left( \frac{\text{Energy at Level } n+1}{\text{Energy at Level } n} \right) \times 100\%

C6H12O6+6O2→6CO2+6H2O+ATPC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP

Percentage Change=New Value−Old ValueOld Value×100\text{Percentage Change} = \frac{\text{New Value} - \text{Old Value}}{\text{Old Value}} \times 100

💡Examples

Problem 1:

In a specific grassland ecosystem, the Net Primary Productivity (NPPNPP) is measured at 20,000 kJ m−2 yr−120,000 \, kJ \, m^{-2} \, yr^{-1}. Using the 10%10\% rule, calculate the energy available to the tertiary consumers.

Solution:

20 kJ m−2 yr−120 \, kJ \, m^{-2} \, yr^{-1}

Explanation:

Starting at the Producers (NPP=20,000 kJ m−2 yr−1NPP = 20,000 \, kJ \, m^{-2} \, yr^{-1}):

  1. Primary Consumers receive 10%10\% of 20,000=2,000 kJ m−2 yr−120,000 = 2,000 \, kJ \, m^{-2} \, yr^{-1}.
  2. Secondary Consumers receive 10%10\% of 2,000=200 kJ m−2 yr−12,000 = 200 \, kJ \, m^{-2} \, yr^{-1}.
  3. Tertiary Consumers receive 10%10\% of 200=20 kJ m−2 yr−1200 = 20 \, kJ \, m^{-2} \, yr^{-1}.

Problem 2:

Explain the role of CO2CO_2 in the enhanced greenhouse effect and its source from human activity.

Solution:

Increased combustion of fossil fuels and deforestation.

Explanation:

Human activities like burning coal and oil release stored carbon as CO2CO_2. This gas absorbs outgoing long-wave radiation (heat) from the Earth's surface and re-radiates it back, increasing the global mean temperature. Deforestation reduces the number of CO2CO_2 'sinks' (trees) that perform photosynthesis.

Problem 3:

A lake experiences a sudden influx of NO3−NO_3^- from agricultural runoff. Describe the biological sequence leading to an 'anoxic' state.

Solution:

NO3− increase→Algal Bloom→Algae Die→Bacterial Decomposition→Oxygen DepletionNO_3^- \text{ increase} \rightarrow \text{Algal Bloom} \rightarrow \text{Algae Die} \rightarrow \text{Bacterial Decomposition} \rightarrow \text{Oxygen Depletion}.

Explanation:

The nitrates act as a limiting nutrient; their increase causes an algal bloom. When the algae die, aerobic bacteria decompose them. These bacteria consume the dissolved O2O_2 in the water for respiration, leading to a high Biological Oxygen Demand (BODBOD) and anoxic conditions where fish cannot survive.