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Human Influences on Ecosystems - Food supply

Grade 11IGCSEBiology

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

🔑Concepts

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Food supply is managed through modern technology like chemical fertilizers containing nitrates (NO3−NO_3^-) and phosphates (PO43−PO_4^{3-}) to increase crop yields.

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Monoculture is the practice of growing a single species, such as ZeaZea maysmays (corn), over a large area, which can lead to a decrease in biodiversity and an increase in pest populations.

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Intensive livestock farming increases efficiency but causes environmental concerns due to the production of greenhouse gases like methane (CH4CH_4) and the leaching of animal waste into water systems.

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Eutrophication occurs when excess fertilizers (leaching of NO3−NO_3^-) enter water bodies, leading to algal blooms, increased bacterial decomposition, and a decrease in dissolved oxygen (O2O_2).

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Habitat destruction for agricultural land leads to the loss of native species, disruption of food chains, and increased soil erosion due to the removal of deep-rooted vegetation.

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Sustainable food production aims to meet the needs of the current population without compromising future resources, often utilizing biological control instead of chemical pesticides.

📐Formulae

Energy Efficiency=Energy available to next trophic levelEnergy available to previous trophic level×100%Energy\ Efficiency = \frac{\text{Energy available to next trophic level}}{\text{Energy available to previous trophic level}} \times 100\%

6CO2+6H2O→light,chlorophyllC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{light, chlorophyll} C_6H_{12}O_6 + 6O_2

Rate of Yield Increase=ΔCrop YieldΔTime\text{Rate of Yield Increase} = \frac{\Delta \text{Crop Yield}}{\Delta \text{Time}}

💡Examples

Problem 1:

Explain why food chains for human consumption are more energy-efficient if humans consume producers (plants) directly rather than primary consumers (livestock).

Solution:

Energy is lost at each trophic level (approximately 90%90\% loss). If humans consume plants, they are at the second trophic level, receiving roughly 10%10\% of the initial energy. If they consume livestock, they are at the third trophic level, receiving only 1%1\% (10%×10%10\% \times 10\%) of the original energy captured from 6CO2+6H2O6CO_2 + 6H_2O.

Explanation:

Shortening the food chain reduces the number of energy transfer steps, thereby decreasing the total energy lost to the environment as heat and waste.

Problem 2:

Describe the chemical impact of nitrate leaching on aquatic ecosystems.

Solution:

  1. Leaching of NO3−NO_3^- into lakes causes rapid growth of algae (algal bloom). 2. Algae block sunlight, killing plants below. 3. Decomposing bacteria multiply and use up dissolved O2O_2 for aerobic respiration. 4. Fish die due to lack of O2O_2.

Explanation:

This process is known as eutrophication. It represents a shift from a balanced ecosystem to one with high Biological Oxygen Demand (BOD) and low biodiversity.

Food supply - Revision Notes & Key Diagrams | IGCSE Grade 11 Biology